Network Working Group J. Hodges
Internet-Draft PayPal
Intended status: Standards Track Feb 2013
Expires: August 5, 2013
Web Security Framework: Problem Statement and Requirements
draft-ietf-websec-framework-reqs-00
Abstract
Web-based malware and attacks are proliferating rapidly on the
Internet. New web security mechanisms are also rapidly growing in
number, although in an incoherent fashion. This document provides a
brief overview of the present situation and the various seemingly
piece-wise approaches being taken to mitigate the threats. It then
provides an overview of requirements as presently being expressed by
the community in various online and face-to-face discussions.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 5, 2013.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Where to Discuss This Draft . . . . . . . . . . . . . . . 4
2. Document Conventions . . . . . . . . . . . . . . . . . . . . . 5
3. Overall Constraints . . . . . . . . . . . . . . . . . . . . . 5
4. Overall Requirements . . . . . . . . . . . . . . . . . . . . . 6
5. Vulnerabilities, Attacks, and Threats . . . . . . . . . . . . 8
5.1. Attacks . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Threats . . . . . . . . . . . . . . . . . . . . . . . . . 9
6. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7. Detailed Functional Requirements . . . . . . . . . . . . . . . 11
8. Extant Policies to Coalesce . . . . . . . . . . . . . . . . . 15
9. Example Concrete Approaches . . . . . . . . . . . . . . . . . 15
10. Security Considerations . . . . . . . . . . . . . . . . . . . 15
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
12. Informative References . . . . . . . . . . . . . . . . . . . . 19
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 21
Appendix B. Discussion References . . . . . . . . . . . . . . . . 21
B.1. Source: Attacks and Threats . . . . . . . . . . . . . . . 21
B.2. Source: Policy Expression Syntax [1] . . . . . . . . . . . 21
B.3. Source: Policy Expression Syntax [2] . . . . . . . . . . . 22
B.4. Source: Tooling . . . . . . . . . . . . . . . . . . . . . 22
B.5. Source: Performance . . . . . . . . . . . . . . . . . . . 23
B.6. Source: Granularity . . . . . . . . . . . . . . . . . . . 23
B.7. Source: Notifications and Reporting . . . . . . . . . . . 23
B.8. Source: Facilitating Separation of Duties . . . . . . . . 24
B.9. Source: Hierarchical Policy Application . . . . . . . . . 24
B.10. Source: Framing Policy Hierarchy, cross-origin,
granularity . . . . . . . . . . . . . . . . . . . . . . . 24
B.11. Source: Policy Delivery [1] . . . . . . . . . . . . . . . 26
B.12. Source: Policy Delivery [2] . . . . . . . . . . . . . . . 26
B.13. Source: Policy Conflict Resolution . . . . . . . . . . . . 27
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 28
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1. Introduction
Over the past few years, we have seen a proliferation of AJAX-based
web applications (AJAX being shorthand for asynchronous JavaScript
and XML), as well as Rich Internet Applications (RIAs), based on so-
called Web 2.0 technologies. These applications bring both luscious
eye-candy and convenient functionality--e.g. social networking--to
their users, making them quite compelling. At the same time, we are
seeing an increase in attacks against these applications and their
underlying technologies [1]. The latter include (but aren't limited
to) Cross-Site-Request Forgery (CSRF) -based attacks [2], content-
sniffing cross-site-scripting (XSS) attacks [3], attacks against
browsers supporting anti-XSS policies [4], clickjacking attacks [5],
malvertising attacks [6], as well as man-in-the-middle (MITM) attacks
against "secure" (e.g. Transport Layer Security (TLS/SSL)-based [7])
web sites along with distribution of the tools to carry out such
attacks (e.g. sslstrip) [8].
During the same time period we have also witnessed the introduction
of new web security indicators, techniques, and policy communication
mechanisms sprinkled throughout the various layers of the Web and
HTTP. We have a new cookie security flag called HTTPOnly [9]. We
have the anti-clickjacking X-Frame-Options HTTP header [10], the
Strict-Transport-Security HTTP header [RFC6797], anti-CSRF headers
(e.g. Origin) [12], an anti-sniffing header (X-Content-Type-Options:
nosniff) [13], various approaches to content restrictions [14] [15]
and notably Mozilla Content Security Policy (CSP; conveyed via a HTTP
header) [16], the W3C's Cross-Origin Resource Sharing (CORS; also
conveyed via a HTTP header) [17], as well as RIA security controls
such as the crossdomain.xml file used to express a site's Adobe Flash
security policy [18]. There's also the Application Boundaries
Enforcer (ABE) [19], included as a part of NoScript [20], a popular
Mozilla Firefox security extension. Sites can express their ABE
rule-set at a well-known web address for downloading by individual
clients [21], similarly to Flash's crossdomain.xml. Amidst this
haphazard collage of new security mechanisms at least one browser
vendor has even devised a new HTTP header that disables one of their
newly created security features: witness the X-XSS-Protection header
that disables the new anti-XSS features [22] in Microsoft's Internet
Explorer 8 (IE8).
Additionally, there are various proposals aimed at addressing other
facets of inherent web vulnerabilities, for example: JavaScript
postMessage-based mashup communications [23], hypertext isolation
techniques [24], and service security policies advertised via the
Domain Name System (DNS) [25]. Going even further, there are efforts
to redesign web browser architectures [26], of which Google Chrome
and IE8 are deployed examples. An even more radical approach is
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exhibited in the Gazelle Web Browser [27], which features a browser
kernel embodied in a multi-principal OS construction providing cross-
principal protection and fair sharing of all system resources.
Not to be overlooked is the fact that even though there is a plethora
of "standard" browser security features--e.g. the Same Origin Policy
(SOP), network-related restrictions, rules for third-party cookies,
content-handling mechanisms, etc. [28]--they are not implemented
uniformly in today's various popular browsers and RIA frameworks
[29]. This makes life even harder for web site administrators in
that allowances must be made in site security posture and approaches
in consideration of which browser a user may be wielding at any
particular time.
Although industry and researchers collectively are aware of all the
above issues, we observe that the responses to date have been issue-
specific and uncoordinated. What we are ending up with looks perhaps
similar to Frankenstein's monster [30]--a design with noble intents
but whose final execution is an almost-random amalgamation of parts
that do not work well together. It can even cause destruction on its
own [31].
Thus, the goal of this document is to define the requirements for a
common framework expressing security constraints on HTTP
interactions. Functionally, this framework should be general enough
that it can be used to unite the various individual solutions above,
and specific enough that it can address vulnerabilities not addressed
by current solutions, and guide the development of future mechanisms.
Overall, such a framework would provide web site administrators the
tools for managing, in a least privilege [33] manner, the overall
security characteristics of their web site/applications when realized
in the context of user agents.
[[ The author(s) understand that many of the references to web
security issues are now somewhat dated and more recent work has
appeared in the literature. Suggestions of references to use in
superseding the ones herein are welcome; references to web security
survey papers would be good. ]]
1.1. Where to Discuss This Draft
Please disscuss this draft on the websec@ietf.org mailing list
[WebSec].
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2. Document Conventions
NOTE: ..is a note to the reader. These are points that should be
expressly kept in mind and/or considered.
[[TODOn: Things to fix (where "n" in "TODOn" is a number). --JeffH]]
We will also be making use of the WebSec WG issue tracker, so use of
the TODO marks will evolve accordingly.
3. Overall Constraints
Regardless of the overall approaches chosen for conveying site
security policies, we believe that to be deployed at Internet-scale,
and to be as widely usable as possible for both novice and expert
alike, the overall solution approach will need to address these three
points of tension:
Granularity:
There has been much debate during the discussion of some policy
mechanisms (e.g. CSP) as to how fine-grained such mechanisms
should be. The argument against fine-grained mechanisms is
that site administrators will cause themselves pain by
instantiating policies that do not yield the intended results.
E.g. simply copying the expressed policies of a similar site.
The claim is that this would occur for various reasons stemming
from the mechanisms' complexity [34].
Configurability:
Not infrequently, the complexity of underlying facilities, e.g.
in server software, is not well-packaged and thus
administrators are obliged to learn more about the intricacies
of these systems than otherwise might be necessary. This is
sometimes used as an argument for "dumbing down" the
capabilities of policy expression mechanisms [34].
Usability:
Research shows that when security warnings are displayed, users
are often given too much information as well as being allowed
to relatively easily bypass the warnings and continue with
their potentially compromising activity [35] [36] [37] [38]
[39]. Thus users have become trained to "click through"
security notifications "in order to get work done", though not
infrequently rendering themselves insecure and perhaps
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compromised [40].
In the next section we discuss various high-level requirements
derived with the guidance of the latter tension points.
4. Overall Requirements
1. Policy conveyance:
in-band:
HTTP header(s) are already presently used to convey policy
to user agents. However, devising generalized, extensible
HTTP security header(s) such that the on-going "bloat" of
the number of disjoint HTTP security headers is mitigated,
is a stated requirement by various parties. Also, then
there would be a documented framework that can be leveraged
as new approaches and/or threats emerge.
It may be reasonable to devise distinct sets of headers to
convey different classes of policies, e.g., web application
content policies (such as [W3C.CR-CSP-20121115]) versus web
application network connection policies (such as
[RFC6797]).
out-of-band:
An out-of-band policy communication mechanism must be
secure and should have two facets, one for communicating
securely out-of-band of the HTTP protocol to allow for
secure client policy store bootstrapping. potential
approaches are factory-installed web browser configuration,
site security policy download a la Flash's crossdomain.xml
and Maone's ABE for Web Authors [21], and DNS-based policy
advertisement leveraging the security ofthe Secure DNS
(DNSSEC) [32].
NOTE: The distinction between in-band and out-of-band signaling
is difficult to characterize because some seemingly out-
of-band mechanisms rely on the same protocols (HTTP/HTTPS)
and infrastructure (e.g., transparent proxy servers) as
the protocols they ostensibly protect.
2. Granularity:
In terms of granularity, vast arrays of stand-alone blog,
wiki, hosted web account, and other "simple" web sites could
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ostensibly benefit from relatively simple, pre-determined
policies. However, complex sites--e.g. payment, ecommerce,
software-as-a-service, mashup sites, etc.--often differ in
various ways, as well as being inherently complex
implementation-wise. One-size-fits-all policies will
generally not work well for them.
Thus, to be effective for a broad array of web site and
application types, some derived requirements are:
the policy expression mechanism should fundamentally
facilitate fine-grained control. For example, CSP
[W3C.CR-CSP-20121115] offers such control.
In order to address the less complex needs of the more
simple classes of web sites, the policy expression
mechanism should have some facility for enabling "canned
policy profiles".
In addition, the configuration facilities of various
components of the web infrastructure can be enhanced to
provide an appropriately simple veneer over the complexity.
3. Configurability:
With respect to configurability, development effort should be
applied to creating easy-to-use administrative interfaces
addressing the simple cases, like those mentioned above, while
providing advanced administrators the tools to craft and
manage fine-grained multi-faceted policies. Thus more casual
or novice administrators can be aided in readily choosing, or
be provided with, safe default policies while other classes of
sites have the tools to craft the detailed policies they
require. Examples of such an approach are Microsoft's
"Packaging Wizard" [41] that easily auto-generates a quite
complicated service deployment descriptor on behalf of less
experienced administrators, and Firefox's simple Preferences
dialog [42] as compared to its detailed about:config
configuration editor page [43]. In both cases, simple usage
by inexperienced users is anticipated and provided for on one
hand, while complex tuning of the myriad underlying
preferences is provided for on the other.
4. Usability:
Much has been learned over the last few years about what does
and does not work with respect to security indicators in web
browsers and web pages, as noted above, these lessons should
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be applied to the security indicators rendered by new proposed
security mechanisms. We believe that in cases of user agents
venturing into insecure situations, their response should be
to fail the connections by default without user recourse,
rather than displaying warnings along with bypass mechanisms,
as is current practice. For example, the Strict Transport
Security specification [RFC6797] suggests the former so-called
"hard-fail" behavior.
5. Vulnerabilities, Attacks, and Threats
This section enumerates vulnerabilities and attacks of concern, and
then illustrates plausible threats that could result from
exploitation of the vulnerabilities. The intent is to illustrate
threats that ought to be mitigated by a web security policy
framework.
The definitions of vulnerability, attack, and threat used in this
document are based on the definitions from [RFC4949], and are
paraphrased here as:
Vulnerability: A flaw or weakness in a system's design,
implementation, or operation and management that
could be exploited.
Attack: An intentional act of vulnerability exploitation,
usually characterized by one or more of: the method
or technique used, and/or the point of initiation,
and/or the method of delivery, etc. For example:
active attack, passive attack, offline attack,
Cross-site Scripting (XSS) attack, SQL injection
attack, etc.
Threat: Any circumstance or event with the potential to
adversely affect a system and its user(s) through
unauthorized access, destruction, disclosure, or
modification of data, or denial of service.
See also Appendix B.1 Source: Attacks and Threats.
5.1. Attacks
These are some of the attacks which are desirable to mitigate via a
web application security framework (see [WASC-THREAT] for a more
complete taxonomy of attacks):
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1. Cross-site-scripting (XSS) [2] [WASC-THREAT-XSS]
2. Cross-Site-Request Forgery (CSRF) [WASC-THREAT-CSRF]
3. Response Splitting [WASC-THREAT-RESP]
4. User Interface Redressing [UIRedress], aka Clickjacking
[Clickjacking].
5. Man-in-the-middle (MITM) attacks against "secure" web
applications, i.e., ones accessed using TLS/SSL [RFC5246]
[WASC-THREAT-TLS] [SSLSTRIP].
6. [[TODO2: more? (e.g. from [WASC-THREAT] ?) --JeffH]]
5.2. Threats
Via attacks exploiting the vulnerabilities above, an attacker can..
1. Obtain a victim's confidential web application credentials (e.g.,
via cookie theft), and use the credentials to impersonate the
victim and enter into transactions, often with the aim of
monetizing the transaction results to the attacker's benefit.
2. Insert themselves as a Man-in-the-Middle (MITM) between victim
and various services, thus is able to instigate, control,
intercept, and attempt to monetize various transactions and
interactions with web applications, to the benefit of the
attacker.
3. Enumerate various user agent information stores, e.g. browser
history, facilitating views of the otherwise confidential habits
of the victim. This information could possibly be used in
various offline attacks against the victim directly. E.g.:
blackmail, denial of services, law enforcement actions, etc.
4. Use gathered information and credentials to construct and present
a falsified persona of the victim (e.g. for character
assassination).
There is a risk of exfiltration of otherwise confidential victim
information with all the threats listed above.
6. Use Cases
This section outlines various example use cases.
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1. I'm a web application site administrator. My web app includes
static user-supplied content (e.g. submitted from user agents via
HTML FORM + HTTP POST), but either my developers don't properly
sanitize user-supplied content in all cases or/and content
injection vulnerabilities exist or materialize (for various
reasons).
This leaves my web app vulnerable to cross-site scripting. I
wish I could set overall web app-wide policies that prevent user-
supplied content from injecting malicious content (e.g.
JavaScript) into my web app.
2. I'm a web application site administrator. My web application is
intended, and configured, to be uniformly served over HTTPS, but
my developers mistakenly keep including content via insecure
channels (e.g. via insecure HTTP; resulting in so-called "mixed
content").
I wish I could set a policy for my web app that prevents user
agents from loading content insecurely even if my web app is
otherwise telling them to do so.
3. I'm a web application site administrator. My site has a policy
that we can only include content from certain trusted providers
(e.g., our CDN, Amazon S3), but my developers keep adding
dependencies on origins I don't trust. I wish I could set a
policy for my site that prevents my web app from accidentally
loading resources outside my whitelist.
4. I'm a web application site administrator. I want to ensure that
my web app is never framed by other web apps.
5. I'm a developer of a web application which will be included (i.e.
framed) by third parties within their own web apps. I would like
to ensure that my web app directs user agents to only load
resources from URIs I expect it to (possibly even down to
specific URI paths), without affecting the containing web app or
any other web apps it also includes.
6. I'm a web application site administrator. My web app frames
other web apps whose behavior, properties, and policies are not
100% known or predictable.
I need to be able to apply policies that both protect my web app
from potential vulnerabilities or attacks introduced by the
framed web apps, and that work to ensure that the desired
interactions between my web app and the framed apps are securely
realized.
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7. [[TODO3: additional use cases to add? --JeffH]]
7. Detailed Functional Requirements
Many of the below functional requirements are extracted from a
discussion on the [public-web-security] mailing list (in early 2011).
Particular messages are cited inline and appropriate quotes extracted
and reproduced here. Inline citations are provided for definitions
of various terms.
The overall functional requirement categories are:
1. Policy mechanism scope
2. Policy expression syntax
3. Tooling
4. Performance
5. Granularity
6. Notifications and reporting
7. Facilitating Separation of Duties
8. Hierarchical Policy Application
9. Policy Delivery
10. Policy Conflict Resolution
[[TODO4: additional functional requirement categories to add?
--JeffH]]
These requirements are discussed in more detail below:
1. Policy mechanism scope and extensibility:
There is a current proliferation of orthogonal atomic
mechanisms intended to solve very specific problems. Web
developers have a hard enough time with security already
without being expected to master a potentially large number
of different security mechanisms, each with their own unique
threat model, implementation and syntax. Not to mention
trying to figure out how they're expected to interact with
each other; e.g., how to manage the gaps and intersections
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between the models.
Thus the desire to have an extensible security policy
mechanism that could evolve as the web evolves, and the
threats that the web faces also evolve. For example, an
extensibility model similar to HTML where the security
protections could grown over time.
See also Appendix B.2 Source: Policy Expression Syntax [1].
2. Policy expression syntax:
The policy expression syntax for a web security framework
should be declarative [DeclLang] (and extensible, as noted
above). This is for simplicity sake, as the alternative to
declarative is procedural/functional, e.g., the class of
language ECMAscript falls into.
See also Appendix B.2 Source: Policy Expression Syntax [1],
and, Appendix B.3 Source: Policy Expression Syntax [2].
3. Tooling:
We will need tools to (idealy) analyze a web application and
generate an initial security policy.
See also Appendix B.4 Source: Tooling.
4. Performance:
Minimizing performance impact is a first-order concern.
See also Appendix B.5 Source: Performance.
5. Granularity:
For example, discriminate between:
+ "inline" script in <head> versus <body>, or not.
+ "inline" script and "src=" loaded script.
+ Classes of "content", e.g. scriptable content, passive
multimedia, nested documents, etc.
See also Appendix B.6 Source: Granularity.
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6. Notifications and Reporting:
Convey to the user agent an identifier (e.g. a URI) denoting
where to send policy violation reports. Could also specify a
DOM event to be dedicated for this purpose.
An ability to specify that a origin's policies are to be
enforced in a "report only" mode will be useful for debugging
policies as well as site-policy interactions. E.g. for
answering the question: "does my policy 'break' my site?".
See also Appendix B.7 Source: Notifications and Reporting.
7. Facilitating Separation of Duties:
Specifically, allowing for Web Site operations/deployment
personnel to apply site policy, rather then having it being
encoded in the site implementation code by side developers/
implementors.
See also Appendix B.8 Source: Facilitating Separation of
Duties.
8. Hierarchical Policy Application:
The notion that policy emitted by the application's source
origin is able to constrain behavior and policies of
contained origins.
See also Appendix B.9 Source: Hierarchical Policy
Application.
9. Framing Policy Hierarchy, cross-origin, granularity,
auditability, roles:
[[TODO5: Need more fully coalesce the source info from
appendix into this item. --JeffH]]
+ "Framing" is a client-side instance notion, where
webapp1's client-side instance (aka "document") loads
another webapp, "webapp2", into an HTML <IFRAME> element.
+ A webapp may wish to never be framed by another webapp.
+ webapps are denoted by "origins" [RFC6454].
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+ an origin can emit policy (i.e. from the server-side
webapp component) to the user agent (i.e. the execution
environment/container for the client-side webapp
component) in at least two fashions: HTML element
attributes, HTTP header fields, ecmascript code. See also
Paragraph 10.
+ Policy expressed via HTML <IFRAME> elements is "fine-
grained" because the webapp can control such policies on
iframe-by-iframe basis. Policies conveyed by HTTP header
fields applies "document-wide" (i.e., to the webapp
client-side instance) as a whole.
+ Note that either or both of the "framing" or "framed"
webapp client-side instance may be an attacker (in which
case the other webapp client-side instance would be
considered a "victim" (whether or not its actual
intentions are malicious or not)).
See also Appendix B.10 Source: Framing Policy Hierarchy,
cross-origin, granularity.
10. Policy Delivery:
[[TODO6: Need more fully coalesce the source info from
appendix into this item, and blend/resolve/contrast with
above item. --JeffH]]
The web application policy must be communicated by the web
application to the user agent. There are various approaches
and they have tradeoffs between security, audience, and
practicality.
See also Appendix B.11 Source: Policy Delivery [1], as well
as, Appendix B.12 Source: Policy Delivery [2].
11. Policy Conflict Resolution:
[[TODO7: Need more fully coalesce the source info from
appendix into this item. --JeffH]]
What is the model for resolving conflicts between policies
expressed by "parent" and "child" webapps?
Should policies conveyed via HTTP header fields (i.e., that
apply webapp-wide) be handled differently than those
expressed by webapp client-side instances (e.g., via HTML
elements and their attributes)?
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See also Appendix B.13 Source: Policy Conflict Resolution.
8. Extant Policies to Coalesce
Presently, this section lists a grab-bag of individually-expressed
web app security policies which a more general substrate could
ostensibly encompass (in order to, for example, reduce "header bloat"
and bytes-on-the-wire issues), as well as reduce functional policy
duplication/overlap.
CORS
XDomainRequest
toStaticHtml
innerSafeHtml
X-Frame-Options
CSP frame-ancestors
more?
9. Example Concrete Approaches
An overall, broad approach (from [0]):
As for an overall policy mechanism, we observe that leveraging a
combination of CSP [16] and ABE [19], or their employment in
tandem, as a starting point for a multi-vendor approach may be
reasonable. For a near-term policy delivery mechanism, we
advocate use of both HTTP headers and a policy file at a well-
known location. Leveraging DNSSEC is attractive in the
intermediate term, i.e. as it becomes more widely deployed.
10. Security Considerations
Security considerations go here.
11. References
[[TODO1: re-code refs into xml and place in proper refs section.
--JeffH]]
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[0] J. Hodges, A. Steingruebl, "The Need for Coherent Web Security
Policy Framework(s)", Web 2.0 Security & Privacy, Oakland CA, 20 May
2010. http://w2spconf.com/2010/papers/p11.pdf
[1] Breach Security, "THE WEB HACKING INCIDENTS DATABASE 2009," Aug.
2009. http://www.breach.com/resources/whitepapers/downloads/
WP_TheWebHackingIncidents-2009.pdf
[2] R. Auger, The Cross-Site Request Forgery (CSRF/XSRF) FAQ, 2007.
http://www.cgisecurity.com/articles/csrf-faq.shtml
[3] A. Barth, J. Caballero, and D. Song, "Secure Content Sniffing for
Web Browsers--or How to Stop Papers from Reviewing Themselves,"
Proceedings of the 30th IEEE Symposium on Security & Privacy,
Oakland, CA: 2009.
[4] D. Goodin, "Major IE8 flaw makes 'safe' sites unsafe -
Microsoft's XSS buster busted," The Register, Nov. 2009. http://
www.theregister.co.uk/2009/11/20/internet_explorer_security_flaw/
[5] J. Grossman, "Clickjacking: Web pages can see and hear you," Oct.
2008. http://jeremiahgrossman.blogspot.com/2008/10/
clickjacking-web-pages-can-see-and-hear.html
[6] W. Salusky, Malvertising, 2007.
http://isc.sans.org/diary.html?storyid=3727
[7] T. Dierks and E. Rescorla, "The Transport Layer Security (TLS)
Protocol Version 1.2," RFC5246, Internet Engineering Task Force, Aug.
2008. http://www.ietf.org/rfc/rfc5246.txt
[8] M. Marlinspike, SSLSTRIP, 2009.
http://www.thoughtcrime.org/software/sslstrip/
[9] Scope of HTTPOnly Cookies.
http://docs.google.com/View?docid=dxxqgkd_0cvcqhsdw
[10] E. Lawrence, IE8 Security Part VII: ClickJacking Defenses, 2009.
http://blogs.msdn.com/ie/archive/2009/01/27/
ie8-security-part-vii-clickjacking-defenses.aspx
[11] J. Hodges, C. Jackson, and A. Barth, "Strict Transport
Security," Work-in-progress, Internet-Draft, Jul. 2010.
http://tools.ietf.org/html/draft-hodges-strict-transport-sec
[12] A. Barth, C. Jackson, and I. Hickson, "The Web Origin Concept,"
Internet-Draft, work in progress, Internet Engineering Task Force,
2009. http://tools.ietf.org/html/draft-abarth-origin
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[13] E. Lawrence, IE8 Security Part VI: Beta 2 Update, 2008. http://
blogs.msdn.com/ie/archive/2008/09/02/
ie8-security-part-vi-beta-2-update.aspx
[14] G. Markham, Content restrictions, 2007.
http://www.gerv.net/security/content-restrictions/
[15] T. Jim, N. Swamy, and M. Hicks, "BEEP: Browser-Enforced Embedded
Policies," Proceedings of the 16th International World Wide Web
Conference, Banff, Alberta, Canada, 2007.
[16] B. Sterne, "Content Security Policy (CSP)," 2011. https://
dvcs.w3.org/hg/content-security-policy/raw-file/bcf1c45f312f/
csp-unofficial-draft-20110303.html
[17] A.V. Kesteren, "Cross-Origin Resource Sharing (CORS)," Mar.
2009. http://www.w3.org/TR/2009/WD-cors-20090317/
[18] Adobe Systems, "Cross-domain policy file specification." http://
learn.adobe.com/wiki/download/attachments/64389123/
CrossDomain_PolicyFile_Specification.pdf?version=1
[19] G. Maone, ABE - Application Boundaries Enforcer, 2009.
http://noscript.net/abe/
[20] G. Maone, NoScript. http://noscript.net/
[21] G. Maone, ABE for Web Authors, 2009.
http://noscript.net/abe/web-authors.html
[22] Microsoft, "Event 1046 - Cross-Site Scripting Filter," MSDN
Library, undated.
http://msdn.microsoft.com/en-us/library/dd565647%28VS.85%29.aspx
[23] A. Barth, C. Jackson, and W. Li, "Attacks on JavaScript Mashup
Communication," Proceedings of the Web 2.0 Security and Privacy
Workshop, 2009.
[24] M. Ter Louw, P. Bisht, and V. Venkatakrishnan, "Analysis of
Hypertext Isolation Techniques for XSS Prevention," Proceedings of
the Web 2.0 Security and Privacy Workshop, 2008 .
[25] A. Ozment, S.E. Schechter, and R. Dhamija, "Web Sites Should Not
Need to Rely on Users to Secure Communications," W3C Workshop on
Transparency and Usability of Web Authentication, 2006.
[26] C. Reis, A. Barth, and C. Pizano, "Browser Security: Lessons
from Google Chrome," ACM Queue, 2009, pp. 1-8.
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[27] H.J. Wang, C. Grier, A. Moshchuk, S.T. King, P. Choudhury, and
H. Venter, "The Multi-Principal OS Construction of the Gazelle Web
Browser," USENIX Security Symposium, 2009.
[28] M. Zalewski, Browser Security Handbook.
http://code.google.com/p/browsersec/
[29] A. Stamos, D. Thiel, and J. Osborne, Living in the RIA World:
Blurring the Line between Web and Desktop Security, BlackHat
presentation, iSecPartners, 2008.
https://www.isecpartners.com/files/RIA_World_BH_2008.pdf
[30] Mary Shelley, "Frankenstein, or The Modern Prometheus," ca.
1831. http://en.wikipedia.org/wiki/Frankenstein%27s_monster
[31] D. Goodin, "cPanel, Netgear and Linksys susceptible to nasty
attack - Unholy Trinity," The Register, 2009.
http://www.theregister.co.uk/2009/08/02/unholy_trinity_csrf/
[32] R. Arends, R. Austein, M. Larson, D. Massey, and S. Rose, "DNS
security introduction and requirements," RFC4033, Internet
Engineering Task Force, Mar. 2005.
http://www.ietf.org/rfc/rfc4033.txt
[33] J.H. Saltzer and M.D. Schroeder, "The Protection of Information
in Computer Systems," Communications of the ACM, vol. 17, Jul. 1974.
[34] I. Hickson and many others, "Comments on the Content Security
Policy specification," discussion on mozilla.dev.security newsgroup.
http://groups.google.com/group/mozilla.dev.security/browse_frm/
thread/
87ebe5cb9735d8ca?tvc=1&
q=Comments+on+the+Content+Security+Policy+specification
[35] S. Egelman, L.F. Cranor, and J. Hong, "You've Been Warned: An
Empirical Study of the Effectiveness of Web Browser Phishing
Warnings," CHI 2008, April 5 - 10, 2008, Florence, Italy, 2008.
[36] S.E. Schechter, R. Dhamija, A. Ozment, and I. Fischer, "The
Emperor's New Security Indicators," Proceedings of the 2007 IEEE
Symposium on Security and Privacy.
[37] R. Dhamija and J.D. Tygar, "The Battle Against Phishing: Dynamic
Security Skins," Proceedings of the 2005 Symposium on Usable Privacy
and Security (SOUPS).
[38] J. Sobey, T. Whalen, R. Biddle, P.V. Oorschot, and A.S. Patrick,
Browser Interfaces and Extended Validation SSL Certificates: An
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Empirical Study, Ottawa, Canada: School of Computer Science, Carleton
University, 2009.
[39] J. Sunshine, S. Egelman, H. Almuhimedi, N. Atri, and L.F.
Cranor, "Crying Wolf: An Empirical Study of SSL Warning
Effectiveness," USENIX Security Symposium, 2009.
[40] C. Jackson and A. Barth, "ForceHTTPS: Protecting High-Security
Web Sites from Network Attacks," Proceedings of the 17th
International World Wide Web Conference (WWW), 2008.
[41] Microsoft, "Packaging Wizard."
http://msdn.microsoft.com/en-us/library/aa157732(office.10).aspx
[42] Mozilla, "Options window."
http://support.mozilla.com/en-US/kb/Options+window
[43] S. Yegulalp, "Hacking Firefox: The secrets of about:config,"
ComputerWorld, May. 2007. http://www.computerworld.com/s/article/
9020880/Hacking_Firefox_The_secrets_of_about_config
12. Informative References
[Clickjacking]
"Clickjacking", Sep 2008,
<http://www.sectheory.com/clickjacking.htm>.
[DeclLang]
"declarative languages", A Dictionary of
Computing Encyclopedia.com, 2004, <http://
www.encyclopedia.com/doc/1O11-declarativelanguages.html>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
RFC 4949, August 2007.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
December 2011.
[RFC6797] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict
Transport Security (HSTS)", RFC 6797, November 2012.
[SSLSTRIP]
Marlinspike, M., "SSLSTRIP", 2009,
<http://www.thoughtcrime.org/software/sslstrip/>.
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[UIRedress]
"Dealing with UI redress vulnerabilities inherent to the
current web", Sep 2008, <http://lists.whatwg.org/
htdig.cgi/whatwg-whatwg.org/2008-September/016284.html>.
[W3C.CR-CSP-20121115]
Sterne, B. and A. Barth, "Content Security Policy 1.0",
World Wide Web Consortium CR CR-CSP-20121115,
November 2012,
<http://www.w3.org/TR/2012/CR-CSP-20121115>.
[WASC-THREAT]
Web Application Security Consortium, "The WASC Threat
Classification v2.0", January 2010,
<http://projects.webappsec.org/f/WASC-TC-v2_0.pdf>.
[WASC-THREAT-CSRF]
Web Application Security Consortium, "Cross Site Request
Forgery", The WASC Threat Classification v2.0 Reference
ID: WASC-9, January 2010, <http://projects.webappsec.org/
w/page/13246919/Cross%20Site%20Request%20Forgery>.
[WASC-THREAT-RESP]
Web Application Security Consortium, "HTTP Response
Splitting", The WASC Threat Classification v2.0 Reference
ID: WASC-25, January 2010, <http://projects.webappsec.org/
w/page/13246931/HTTP%20Response%20Splitting>.
[WASC-THREAT-TLS]
Web Application Security Consortium, "Insufficient
Transport Layer Protection", The WASC Threat
Classification v2.0 Reference ID: WASC-04, January 2010, <
http://projects.webappsec.org/w/page/13246945/
Insufficient%20Transport%20Layer%20Protection>.
[WASC-THREAT-XSS]
Web Application Security Consortium, "Cross Site
Scripting", The WASC Threat Classification v2.0 Reference
ID: WASC-8, January 2010, <http://projects.webappsec.org/
w/page/13246920/Cross%20Site%20Scripting>.
[WebSec] "Web HTTP Application Security Minus Authentication and
Transport",
<https://www.ietf.org/mailman/listinfo/websec>.
[public-web-security]
"public-web-security@w3.org: Improving standards and
implementations to advance the security of the Web.",
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<http://lists.w3.org/Archives/Public/
public-web-security/>.
Appendix A. Acknowledgments
Text and ideas were prototypically incorporated from various mailing
list discussions, notably the ones on the [public-web-security]
mailing list in early 2011, into this document. The authors wish to
acknowledge and thank these individuals in particular for their tacit
contributions to this document: Lucas Adamski, Adam Barth, gaz Heyes,
Andrew Steingruebl, Brandon Sterne, Daniel Veditz, John Wilander.
Appendix B. Discussion References
B.1. Source: Attacks and Threats
In terms of defining threats in contrast to attacks:
<"Re: More on XSS mitigation (was Re: XSS mitigation in browsers)"
(Lucas Adamski). http://lists.w3.org/Archives/Public/
public-web-security/2011Jan/0089.html>
"... There's a fundamental question about whether we should be
looking at these problems from an attack vs threat standpoint. An
attack is [exploitation of, ed.] XSS [or CSRF, or Response
Splitting, etc.]. A threat is that an attacker could compromise a
site via content injection to trick the user to disclosing
confidential information (by injecting a plugin or CSS to steal
data or fool the user into sending their password to the
attacker's site). ..."
B.2. Source: Policy Expression Syntax [1]
In terms of policy expression syntax and extensibility, Lucas Adamski
supplied this: <"Re: XSS mitigation in browsers" (Lucas Adamski). ht
tp://lists.w3.org/Archives/Public/public-web-security/2011Jan/
0066.html>
"On a conceptual level, I am not really a believer in the current
proliferation of orthogonal atomic mechanisms intended to solve
very specific problems. Security is a holistic discipline, and so
I'm a big supporter of investing in an extensible declarative
security policy mechanism that could evolve as the web and the
threats that it faces do. Web developers have a hard enough time
with security already without being expected to master a
potentially large number of different security mechanisms, each
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with their own unique threat model, implementation and syntax.
Not to mention trying to figure out how they're expected to
interact with each other... how to manage the gaps and
intersections between the models."
B.3. Source: Policy Expression Syntax [2]
In terms of policy expression syntax and extensibility, Adam Barth
supplied this: <"Re: Scope and complexity (was Re: More on XSS
mitigation)" (Adam Barth). http://lists.w3.org/Archives/Public/
public-web-security/2011Jan/0108.html>
"I guess I wish we had an extensibility model more like HTML where
we could grow the security protections over time. For example, we
can probably agree that both <canvas> and <video> are great
additions to HTML that might not have made sense when folks were
designing HTML 1.0.
As long as you're not relying on the security policy as a first
line of defense, the extensibility story for security policies is
even better than it is with HTML tags. With an HTML tag, you need
a fall-back for browsers that don't support the tag, whereas with
a security policy, you'll always have your first line of defense.
Ideally, we could come up with a policy mechanism that let us nail
XSS today and that fostered innovation in security for years to
come. In the short term, you could view the existing CSP features
(e.g., clickjacking protection) as the first wave of innovation.
If those pieces are popular, then it should be easy for other
folks to adopt them."
B.4. Source: Tooling
In terms of tooling needs, John Wilander supplied this: <"Re: More on
XSS mitigation" (John Wilander). http://lists.w3.org/Archives/
Public/public-web-security/2011Jan/0082.html>
"*Developers Will Want a Policy Generator* A key issue for in-the-
field success of CSP is how to write, generate and maintain the
policies. Just look at the epic failure of Java security
policies. The Java policy framework was designed for static
releases shipped on CDs, not for moving code, added frameworks,
new framework versions etc. The world of web apps is so dynamic
I'm still amazed. If anything, for instance messy security
policies, gets in the way of daily releases it's a no go. At
least until there's an exploit. Where am I going with this?
Well, we should implement a PoC *policy generator* and run it on
some fairly large websites before we nail the standard. There
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will be subtleties found which we can address and we can bring the
PoC to production level while the standard is being finalized and
shipped in browsers. Then we release the policy generator along
with policy enforcement -- success! "
B.5. Source: Performance
In terms of performance, John Wilander supplied this: <"Re: More on
XSS mitigation" (John Wilander). http://lists.w3.org/Archives/
Public/public-web-security/2011Jan/0082.html>
"*We Mustn't Spoil Performance* Web developers (and browser
developers) are so hung up on performance that we really need to
look at what they're up to and make sure we don't spoil things.
Especially load performance now that it's part of Google's
rating."
B.6. Source: Granularity
In terms of granularity, Daniel Veditz supplied this: <"Proposal to
move the debate forward" (Daniel Veditz). http://lists.w3.org/
Archives/Public/public-web-security/2011Jan/0122.html>
"We oscillated several times between lumpy and granular. Fewer
classes (simpler) is always more attractive, easier to explain and
understand. The danger is that future features then end up being
added to the existing lumps, possibly enabling things that the
site isn't aware they need to now filter. It's a constant problem
as we expand the capabilities of browsers -- sites that used to be
perfectly secure are suddenly hackable because all the new
browsers added feature-X."
B.7. Source: Notifications and Reporting
In terms of notifications and reporting, Brandon Sterne supplied
this: <"[Content Security Policy] Proposal to move the debate
forward" (Brandon Sterne). http://lists.w3.org/Archives/Public/
public-web-security/2011Jan/0118.html>
"...
3. Violation Reporting
a. report-uri: URI to which a report will be sent upon policy
violation
b. SecurityViolation event: DOM event fired upon policy violations
..."
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B.8. Source: Facilitating Separation of Duties
In terms of facilitating separation of duties, Andrew Steingruebl
supplied this: <"RE: Content Security Policy and iframe@sandbox"
(Andrew Steingruebl). http://lists.w3.org/Archives/Public/
public-web-security/2011Feb/0050.html>
"... 2. SiteC is also totally in control of all HTTP headers it
emits. It could just as easily indicate policy choices for all
frames via CSP. It could advertise a blanket policy (No JS, No
ActiveX). Advertising a page-specific, or frame/target specific
policy is substantially more difficult and probably unwieldy.
But, depending on how SiteC is configured, setting a global site
policy via headers offers a potential separation of duties that #1
does not, it allows website admin to specific things that each web
developer might not be able to. ..."
B.9. Source: Hierarchical Policy Application
In terms of hierarchical policy application, Andrew Steingruebl
supplied this: <"RE: Content Security Policy and iframe@sandbox"
(Andrew Steingruebl). http://lists.w3.org/Archives/Public/
public-web-security/2011Feb/0048.html>
"... I could imagine a tweak to CSP wherein CSP would control all
contents hierarchically. I already spoke to Brandon about it, but
it was just a quick brainstorm.
You could imagine revoking permissions in the frame hierarchy and
not granting them back. This does start to get awfully ugly, but
just as CSP controls loading policy for itself, it could also
control loading policy for children, ..."
B.10. Source: Framing Policy Hierarchy, cross-origin, granularity
In terms of framing policy hierarchy, cross-origin, granularity, Andy
Steingruebl and Adam Barth supplied this:
<"Re: Content Security Policy and iframe@sandbox") (Andy
Steingruebl, Adam Barth) http://lists.w3.org/Archives/Public/
public-web-security/2011Feb/0051.html>
On Sat, Feb 12, 2011 at 9:01 PM, Steingruebl, Andy
<asteingruebl@paypal-inc.com> wrote:
>> -----Original Message-----
>> From: Adam Barth [mailto:w3c@adambarth.com]
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>
>> That all sounds very abstract. If you have some concrete examples,
>> that might be more productive to discuss. When enforcing policy
>> supplied by one origin on another origin, we need to be careful to
>> consider the case where the policy providing origin is the attacker
>> and the origin on which the policy is being enforced is the victim.
>
> SiteA wants to make sure it cannot ever be framed. It deploys
X-Frame-Options headers and framebusting JS, and maybe even CSP
frame-ancestors.
>
> SiteB wants to make sure it never loads data from anything other than
SiteB (no non-origin loads). It outputs CSP headers to this effect
>
> SiteC wants to make sure that any content it frames cannot run ActiveX
controls, nor do a 401 authentication. It can't really do this with
current iframe sandboxing, but pretend it could...
>
> SiteC wants to control the behavior of children that it frames. It
needs to advertise this policy to a web browser. It has two choices:
>
> 1. It can do it inline in the HTML it outputs with extra attributes of
the iframe it creates. SiteC is in complete control of the HTML that
creates the iframe. I can impose any policy via sandbox attributes.
Currently for example, it can disable JS in the frame. If it frames
SiteA, SiteA's framebusting JS will never run, but the browser will
respect its X-Frame-Options headers.
>
> 2. SiteC is also totally in control of all HTTP headers it emits. It
could just as easily indicate policy choices for all frames via CSP. It
could advertise a blanket policy (No JS, No ActiveX). Advertising a
page-specific, or frame/target specific policy is substantially more
difficult and probably unwieldy. But, depending on how SiteC is
configured, setting a global site policy via headers offers a potential
separation of duties that #1 does not, it allows website admin to
specific things that each web developer might not be able to.
>
> 3. Because all of Site A,B,C are in different origins, they don't
really have to worry about polluting other origins, but they do have to
worry about problematic behavior such as top-nav, 401-auth popups, etc.
Parents need to constrain certain behavior of things they embed,
according to certain rules of whether the child allows itself to be
framed.
>
> I totally get how existing iframe sandboxing that turns off JS is
problematic for sites [due to] older browsers that don't support
X-Frame-Options. We already have a complicated interaction between
these multiple security controls.
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>
> Can you give me an example of why my #1/#2 are actually that
different? Whether we control behavior with headers of inline content,
each site is totally responsible for what it emits, and can already
control in some interesting ways the behavior of content it
frames/includes.
In this example, the trade-off for Site C seems to boil down to the
granularity of the policy. Using attributes on a frame is more
fine-grained because Site C can make these decisions on an
iframe-by-iframe basis whereas using a document-wide policy is more
coarse-grained.
Of course, there's a trade-off between different granularities. On
the one hand, fine-grained gives the site more control over how
different iframes behavior. On the other hand, it's much easier to
audit and understand the effects of a coarse-grained policy.
Adam
B.11. Source: Policy Delivery [1]
In terms of policy delivery, Brandon Sterne supplied this: <"[Content
Security Policy] Proposal to move the debate forward" (Brandon
Sterne). http://lists.w3.org/Archives/Public/public-web-security/
2011Jan/0118.html>
"...
6. Policy delivery
a. HTTP header
b. <meta> (or <link>) tag, to be superseded by header if present
c. policy-uri: a URI from which the policy will be fetched; can be
specified in either header or tag
..."
B.12. Source: Policy Delivery [2]
In terms of defining policy delivery, gaz Heyes supplied this: <"Re:
[Content Security Policy] Proposal to move the debate forward" (gaz
Heyes). http://lists.w3.org/Archives/Public/public-web-security/
2011Jan/0148.html>
"...
a) Policy shouldn't be defined in a http header it's too messy and
what happens when there's a mistake?
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b) As discussed on the list there is no need to have a separate
method as it can be generated by an attacker. If a policy doesn't
exist then an attacker can now DOS the web site via meta.
c) We have a winner, a http header specifying a link to the policy
file is the way to go IMO, my only problem with it is devs
implementing it. Yes facebook would and probably twitter would
but Dave's tea shop wouldn't pay enough money to hire a web dev
who knew how to implement a custom http header yet they would know
how to validate HTML. So the question is are we bothered about
little sites that are likely to have nice tea and XSS holes? If
so I suggest updating the HTML W3C validator to require a security
policy to pass validation if not I suggest a policy file delivered
by http header.
..."
B.13. Source: Policy Conflict Resolution
In terms of defining policy conflict resolution, Andrew Steingruebl
supplied this: <"RE: Content Security Policy and iframe@sandbox"
(Andrew Steingruebl). http://lists.w3.org/Archives/Public/
public-web-security/2011Feb/0048.html>
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> -----Original Message-----
> From: public-web-security-request@w3.org [mailto:public-web-security-
> request@w3.org] On Behalf Of Adam Barth
>
> @sandbox and CSP are very different. The primary difference is who
> choses the policy. In the case of @sandbox, the embedder chooses
> the policy. In CSP, the provider of the resource chooses the policy.
While this is true today, I could imagine a tweak to CSP wherein CSP
would control all contents hierarchically. I already spoke to Brandon
about it, but it was just a quick brainstorm.
You could imagine revoking permissions in the frame hierarchy and not
granting them back. This does start to get awfully ugly, but just as
CSP controls loading policy for itself, it could also control loading
policy for children, right?
Fundamentally, since the existing security model doesn't really provide
for strict separation of parent/child (popups, 401's, top-nav) CSP and
iframe sandbox both try to control the behavior of resources we pull
from other parties.
Do we think that these are both special cases of a general security
policy (my intuition says yes) or that they have some quite orthogonal
types of security controls that cannot be mixed into a single policy
declaration?
One clear problem that comes to mind is that there are policies that
come from the "child" such as X-Frame-Options that must break the
ordinary parent/child relationship from a precedence standpoint.
Author's Address
Jeff Hodges
PayPal
2211 North First Street
San Jose, California 95131
US
Email: Jeff.Hodges@PayPal.com
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