IPv6 Operations M. Gysi
Internet-Draft Swisscom
Intended status: Informational G. Leclanche
Expires: June 8, 2014 Viagenie
E. Vyncke, Ed.
Cisco Systems
R. Anfinsen
Altibox
December 05, 2013
Balanced Security for IPv6 Residential CPE
draft-ietf-v6ops-balanced-ipv6-security-01
Abstract
This document describes how an IPv6 residential Customer Premise
Equipment (CPE) can have a balanced security policy that allows for a
mostly end-to-end connectivity while keeping the major threats
outside of the home. It is documenting an existing IPv6 deployment
by Swisscom and allows all packets inbound/outbound EXCEPT for some
layer-4 ports where attacks and vulnerabilities (such as weak
passwords) are well-known. The policy is a proposed set of rules
that can be used as a default setting. The set of blocked inbound
and outbound ports is expected to be updated as threats come and go.
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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This Internet-Draft will expire on June 8, 2014.
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Copyright Notice
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This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Threats . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Rules for Balanced Security Policy . . . . . . . . . . . 4
3.2. Rules Example for Layer-4 Protection: Swisscom
Implementation . . . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. Informative References . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Internet access in residential IPv4 deployments generally consists of
a single IPv4 address provided by the service provider for each home.
The residential CPE then translates the single address into multiple
private IPv4 addresses allowing more than one device in the home, but
at the cost of losing end-to-end reachability. IPv6 allows all
devices to have a globally unique IP address, restoring end-to-end
reachability directly between any device. Such reachability is very
powerful for ubiquitous global connectivity, and is often heralded as
one of the significant advantages to IPv6 over IPv4. Despite this,
concern about exposure to inbound packets from the IPv6 Internet
(which would otherwise be dropped by the address translation function
if they had been sent from the IPv4 Internet) remain.
This difference in residential default internet protection between
IPv4 and IPv6 is a major concern to a sizable number of ISPs and the
security policy described in this document addresses this concern
without damaging IPv6 end-to-end connectivity.
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The security model provided in this document is meant to be used as a
pre-registered setting and potentially default one for IPv6 security
in CPEs. The model departs from the "simple security" model
described in [RFC6092] . It allows most traffic, including incoming
unsolicited packets and connections, to traverse the CPE unless the
CPE identifies the traffic as potentially harmful based on a set of
rules. This policy has been deployed as a default setting in
Switzerland by Swisscom for residential CPEs.
This document can be applicable to off-the-shelves CPE as well as to
managed Service Provider CPE or for mobile Service Providers (where
it can be centrally implemented).
2. Threats
For a typical residential network connected to the Internet over a
broadband or mobile connection, the threats can be classified into:
o denial of service by packet flooding: overwhelming either the
access bandwidth or the bandwidth of a slower link in the
residential network (like a slow home automation network) or the
CPU power of a slow IPv6 host (like networked thermostat or any
other sensor type nodes);
o denial of service by Neighbor Discovery cache exhaustion
[RFC6583]: the outside attacker floods the inside prefix(es) with
packets with a random destination address forcing the CPE to
exhaust its memory and its CPU in useless Neighbor Solicitations;
o denial of service by service requests: like sending print jobs
from the Internet to an ink jet printer until the ink cartridge is
empty or like filing some file server with junk data;
o unauthorized use of services: like accessing a webcam or a file
server which are open to anonymous access within the residential
network but should not be accessed from outside of the home
network or accessing to remote desktop or SSH with weak password
protection;
o exploiting a vulnerability in the host in order to get access to
data or to execute some arbitrary code in the attacked host;
o trojanized host (belonging to a Botnet) can communicate via a
covert channel to its master and launch attacks to Internet
targets.
3. Overview
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The basic goal is to provide a pre-defined security policy which aims
to block known harmful traffic and allow the rest, restoring as much
of end-to-end communication as possible. This pre-defined policy
should be centrally updated, as threats are changing over time. It
could also be a member of a list of pre-defined security policies
available to an end-customer, for example together with "simple
security" from [RFC6092] and a "strict security" policy denying
access to all unexpected input packets.
3.1. Rules for Balanced Security Policy
These are an example set of generic rules to be applied. Each would
normally be configurable, either by the user directly or on behalf of
the user by a subscription service. This document does not address
the statefulness of the filtering rules as its main objective is to
present an approach where some protocols (identified by layer-4
ports) are assumed weak or malevolent and therefore are blocked while
all other protocols are assumed benevolent and are permitted.
If we name all nodes on the residential side of the CPE as 'inside'
and all nodes on the Internet as 'outside', and any packet sent from
outside to inside as being 'inbound' and 'outbound' in the other
direction, then the behavior of the CPE is described by a small set
or rules:
1. Rule RejectBogon: apply ingress filtering in both directions per
[RFC3704] and [RFC2827] for example with unicast reverse path
forwarding (uRPF) checks (anti-spoofing) for all inbound and
outbound traffic (implicitly blocking link-local and ULA in the
same shot), as described in Section 2.1 Basic Sanitation and
Section 3.1 Stateless Filters of [RFC6092];
2. Rule AllowManagement: if the CPE is managed by the SP, then allow
the management protocols (SSH, SNMP, syslog, TR-069, IPfix, ...)
from/to the SP Network Operation Center;
3. Rule ProtectWeakServices: drop all inbound and outbound packets
whose layer-4 destination is part of a limited set (see
Section 3.2), the intent is to protect against the most common
unauthorized access and avoid propagation of worms; an advanced
residential user should be able to modify this pre-defined list;
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4. Rule Openess: allow all unsolicited inbound packets with rate
limiting the initial packet of a new connection (such as TCP SYN,
SCTP INIT or DCCP-request, not applicable to UDP) to provide very
basic protection against SYN port and address scanning attacks.
All transport protocols and all non-deprecated extension headers
are accepted. This is a the major deviation from REC-11, REC-17
and REC-33 of [RFC6092].
5. All requirements of [RFC6092] except REC-11, REC-18 and REC-33
must be supported.
3.2. Rules Example for Layer-4 Protection: Swisscom Implementation
As of 2013, Swisscom has implemented the rule ProtectWeakService as
described below. This is meant as an example and must not be
followed blindly: each implementer has specific needs and
requirements. Furthermore, the example below will not be updated as
time passes, whereas threats will evolve.
+-----------+------+-----------------------------------+
| Transport | Port | Description |
+-----------+------+-----------------------------------+
| tcp | 22 | Secure Shell (SSH) |
| tcp | 23 | Telnet |
| tcp | 80 | HTTP |
| tcp | 3389 | Microsoft Remote Desktop Protocol |
| tcp | 5900 | VNC remote desktop protocol |
+-----------+------+-----------------------------------+
Table 1: Drop Inbound
+-----------+------+-----------------------------------+
| Transport | Port | Description |
+-----------+------+-----------------------------------+
| tcp-udp | 88 | Kerberos |
| tcp | 111 | SUN Remote Procedure Call |
| tcp | 135 | MS Remote Procedure Call |
| tcp | 139 | NetBIOS Session Service |
| tcp | 445 | Microsoft SMB Domain Server |
| tcp | 513 | Remote Login |
| tcp | 514 | Remote Shell |
| tcp | 548 | Apple Filing Protocol over TCP |
| tcp | 631 | Internet Printing Protocol |
| udp | 1900 | Simple Service Discovery Protocol |
| tcp | 2869 | Simple Service Discovery Protocol |
| udp | 3702 | Web Services Dynamic Discovery |
| udp | 5353 | Multicast DNS |
| udp | 5355 | Link-Lcl Mcast Name Resolution |
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+-----------+------+-----------------------------------+
Table 2: Drop Inbound and Outbound
Choosing services to protect is not an easy task, and as of 2013
there is no public service proposing a list of ports to use in such a
policy. The Swisscom approach was to think in terms of services, by
defining a list of services that are LAN-Only (ex: Multicast DNS)
whose communication is denied by the policy both inbound and
outbound, and a list of services that are known to be weak or
vulnerable like management protocols that could be activated
unbeknownst to the user.
The process used to set-up and later update the filters is out of
scope of this document. The update of the specific rules could be
done together with a firmware upgrade or by a policy update (for
example using Broadband Forum TR-069).
Among other sources, [DSHIELD] was used by Swisscom to set-up their
filters. Another source of information could be the appendix A of
[TR124]. The L4-filter as described does not block GRE tunnels
([RFC2473]) so this is a deviation from [RFC6092].
Note: the authors believe that with a dozen of rules only, a naive
and unaware residential subscriber would be reasonably protected. Of
course, technically-aware susbcribers should be able to open other
applications (identified by their layer-4 ports or IP protocol
numbers) through their CPE using some kind of user interface or even
to select a completely different security policy such as the open or
'closed' policies defined by [RFC6092]. This is the case in the
Swisscom deployment.
It is worth mentioning that PCP ([RFC6887]), UPnP ([IGD]) and similar
protocols can also be used to dynamically override the default rules.
4. IANA Considerations
There are no extra IANA consideration for this document.
5. Security Considerations
The security policy protects from the following type of attacks:
o Unauthorized access because vulnerable ports are blocked
Depending on the extensivity of the filters, certain vulnerabilities
could be protected or not. It does not preclude the need for end-
devices to have proper host-protection as most of those devices
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(smartphones, laptops, etc.) would anyway be exposed to completely
unfiltered internet at some point of time. The policy addresses the
major concerns related to the loss of stateful filtering imposed by
IPV4 NAPT when enabling public globally reachable IPv6 in the home.
To the authors' knowledge, there has not been any incident related to
this deployment in Swisscom network, and no customer complaints have
been registered.
This set of rules cannot help with the following attacks:
o Flooding of the CPE access link;
o Malware which is fetched by inside hosts on a hostile web site
(which is in 2013 the majority of infection sources).
6. Acknowledgements
The authors would like to thank several people who initiated the
discussion on the ipv6-ops@lists.cluenet.de mailing list and others
who provided us valuable feedback and comments, notably: Tore
Anderson, Rajiv Asati, Fred Baker, Lorenzo Colitti, Paul Hoffman,
Merike Kaeo, Simon Leinen, Eduard Metz, Martin Millnert, Benedikt
Stockebrand. Thanks as well to the following SP that discussed with
the authors about this technique: Altibox, Swisscom and Telenor.
7. Informative References
[DSHIELD] DShield, "Port report: DShield", <https://
secure.dshield.org/portreport.html?sort=records>.
[IGD] UPnP Forum, "WANIPConnection:2 Service", December 20110,
<http://upnp.org/specs/gw/UPnP-gw-
WANIPConnection-v2-Service.pdf>.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, March 2004.
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[RFC6092] Woodyatt, J., "Recommended Simple Security Capabilities in
Customer Premises Equipment (CPE) for Providing
Residential IPv6 Internet Service", RFC 6092, January
2011.
[RFC6583] Gashinsky, I., Jaeggli, J., and W. Kumari, "Operational
Neighbor Discovery Problems", RFC 6583, March 2012.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
2013.
[TR124] Broadband Forum, "Functional Requirements for Broadband
Residential Gateway Devices", December 2006, <http://www
.broadband-forum.org/technical/download/TR-124.pdf>.
Authors' Addresses
Martin Gysi
Swisscom
Binzring 17
Zuerich 8045
Switzerland
Phone: +41 58 223 57 24
Email: Martin.Gysi@swisscom.com
Guillaume Leclanche
Viagenie
246 Aberdeen
Quebec, QC G1R 2E1
Canada
Phone: +1 418 656 9254
Email: guillaume.leclanche@viagenie.ca
Eric Vyncke (editor)
Cisco Systems
De Kleetlaan 6a
Diegem 1831
Belgium
Phone: +32 2 778 4677
Email: evyncke@cisco.com
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Ragnar Anfinsen
Altibox
Breiflaatveien 18
Stavanger 4069
Norway
Phone: +47 93488235
Email: Ragnar.Anfinsen@altibox.no
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