NSIS A. Fessi
Internet-Draft M. Stiemerling
Expires: December 30, 2004 NEC
S. Thiruvengadam
H. Tschofenig
Siemens
C. Aoun
Nortel Networks
July 2004
Security Threats for the NATFW NSLP
draft-fessi-nsis-natfw-threats-02
Status of this Memo
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on December 30, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
Opening a firewall pinhole or creating a NAT binding is a very
security sensitive issue. This memo identifies security threats and
security requirements that need to be addressed for the NATFW NSLP.
Generic security threats to the NSIS protocols have been already
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 1]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
discussed in the NSIS Working Group.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Attacks related to authentication and authorization . . . . . 4
3.1 Data Sender (DS) behind a firewall . . . . . . . . . . . . 6
3.2 Data Sender (DS) behind a NAT . . . . . . . . . . . . . . 7
3.3 Data Receiver (DR) behind a firewall . . . . . . . . . . . 7
3.4 Data Receiver (DR) behind a NAT . . . . . . . . . . . . . 9
3.5 NSLP message injection . . . . . . . . . . . . . . . . . . 11
4. Denial-of-Service Attacks . . . . . . . . . . . . . . . . . . 11
4.1 Flooding with CREATE messages from outside . . . . . . . . 11
4.1.1 Attacks due to NSLP state . . . . . . . . . . . . . . 11
4.1.2 Attacks due to authentication complexity . . . . . . . 12
4.1.3 Attacks to the endpoints . . . . . . . . . . . . . . . 12
4.1.4 Attacks to the NTLP . . . . . . . . . . . . . . . . . 12
4.2 Flooding with REA messages from inside . . . . . . . . . . 12
5. Man-in-the-Middle Attacks . . . . . . . . . . . . . . . . . . 13
6. Message Modification . . . . . . . . . . . . . . . . . . . . . 14
7. Session Modification/Deletion . . . . . . . . . . . . . . . . 15
7.1 Misuse of mobility in NAT handling . . . . . . . . . . . . 16
8. Misuse of unreleased sessions . . . . . . . . . . . . . . . . 18
9. Data traffic injection . . . . . . . . . . . . . . . . . . . . 20
10. Eavesdropping and traffic analysis . . . . . . . . . . . . . 21
11. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . 22
12. Security Considerations . . . . . . . . . . . . . . . . . . 22
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 22
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
14.1 Normative References . . . . . . . . . . . . . . . . . . . . 22
14.2 Informative References . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 23
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 2]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
Intellectual Property and Copyright Statements . . . . . . . . 25
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 3]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
1. Introduction
This document provides an analysis of the security threats that are
specific for the NATFW NSLP. The NATFW NSLP is used to install the
required policy rules (firewall pinhole and/or NAT binding) on
middleboxes along the path to allow the traversal of a data flow.
Opening a pinhole in the firewall or creating a NAT binding is a very
security sensitive issue. Thus, we need to examine carefully who is
allowed to install these policy rules and what security threats need
to be addressed. In this document we will analyze different types of
possible attacks to networks running NSIS for middlebox
configuration.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [5].
Furthermore, we use the same terminology as in [1], [3] and [4].
3. Attacks related to authentication and authorization
As described in [1] the NSIS message which installs policy rules at a
middlebox is the CREATE message. The CREATE message travels from the
Data Sender (DS) toward the Data Receiver (DR). The packet filter or
NAT binding is marked as pending by the middleboxes along the path.
If it is confirmed with a success RESPONSE message from the DR the
requested policy rules on the middleboxes are installed to allow the
traversal of a data flow.
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 4]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
+-----+ +-----+ +-----+
| DS | | MB | | DR |
+-----+ +-----+ +-----+
| | |
| CREATE | CREATE |
|-------------------->+-------------------->|
| | |
| Succeeded/Error | Succeeded/Error |
|<--------------------+<--------------------|
| | |
==========================================>
Direction of data traffic
Figure 1: CREATE Mode
In this section we will consider some simple scenarios for middlebox
configuration:
o Data Sender (DS) behind a firewall
o Data Sender (DS) behind a NAT
o Data Receiver (DR) behind a firewall
o Data Receiver (DR) behind a NAT
A real scenario could include a combination of one or more cases
together, i.e., DS and/or DR is behind a chain of NATs and firewalls.
Figure 2 shows such a possible scenario:
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 5]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
+-------------------+ +--------------------+
| | | |
| Network A | | Network B |
| | | |
| +-----+ | //-----\\ | +-----+ |
| | MB2 |--------+----| INET |----+--------| MB3 | |
| +-----+ | \\-----// | +-----+ |
| | | | | |
| +-----+ | | +-----+ |
| | MB1 | | | | MB4 | |
| +-----+ | | +-----+ |
| | | | | |
| +-----+ | | +-----+ |
| | DS | | | | DR | |
| +-----+ | | +-----+ |
| | | |
+-------------------+ +--------------------+
MB: Middle box (NAT or Firewall or a combination)
DS: Data Sender
DR: Data Receiver
Figure 2: Several middleboxes per network
3.1 Data Sender (DS) behind a firewall
+------------------------------+
| |
| +-----+ create +-----+
| | DS | --------------> | FW |
| +-----+ +-----+
| |
+------------------------------+
Figure 3: DS behind a firewall
DS sends a CREATE message to request the traversal of a data flow.
It is up to network operators to decide how far they can trust users
inside their networks. However, there are several reasons why they
should not.
The following attacks are possible:
o DS could open a firewall pinhole with a source address different
from its own host.
o DS could open firewall pinholes for incoming data flows that are
not supposed to enter the network.
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 6]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
o DS could request installation of any policy rules and allow all
traffic go through.
SECURITY REQUIREMENT: As already mentioned in [1] Section (3.2), the
middlebox MUST authenticate and authorize the neighboring NAT/FW NSLP
node which requests an action. Authentication and authorization of
the initiator SHOULD be provided to NATs and Firewalls along the path
as motivated with Section 2.2.3 of [1].
3.2 Data Sender (DS) behind a NAT
The case 'DS behind a NAT' is analogous to the case 'DS behind a
firewall'.
It is worth mentioning that authentication based on IP address is not
possible if NATs are deployed. Figure 4 illustrates such a scenario:
+------------------------------+
| |
| +------+ CREATE |
| | NI_1 | ------\ +-----+ CREATE +-----+
| +------+ \------> | NAT |-------->| MB |
| +-----+ +-----+
| +------+ |
| | NI_2 | |
| +------+ |
+------------------------------+
Figure 4: Several NIs behind a NAT
In this case the middlebox MB does not know who is the NSIS Initiator
since both NI_1 and NI_2 are behind a NAT. Authentication needs to
be provided by other means such as the NSLP or the application layer.
SECURITY REQUIREMENT: The middlebox MUST authenticate and ensure that
the neighboring NAT/FW NSLP node is authorized to request an action.
Authentication and authorization of the initiator (which is the DR in
this scenario) MAY be provided to the middleboxes.
3.3 Data Receiver (DR) behind a firewall
In this case a CREATE message comes from an entity DS outside the
network towards the DR inside the network.
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 7]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
+------------------------------+
| |
+-----+ CREATE +-----+ CREATE +-----+ |
| DS | -------------> | FW | -------------> | DR | |
+-----+ <------------- +-----+ <------------- +-----+ |
success RESPONSE | success RESPONSE |
| |
+------------------------------+
Figure 5: DR behind a firewall
According to [1] (Section 3.3) "Policy rules at middleboxes MUST be
only installed upon receiving a successful response of type success
RESPONSE".
This means that the middlebox waits until the Data Receiver DR
confirms the request of the Data Sender DS with a success RESPONSE
message. This is, however, only necessary
o if the policy rule creation/deletion/update at a firewall along
the path cannot be authorized and
o if the middlebox is still forwarding the signaling message towards
the end host (without state creation/deletion/modification).
This confirmation implies that the data receiver is expecting the
data flow.
At this point we differentiate 2 cases:
1. DR knows the IP address of the DS (for instance because of some
previous application layer signaling) and is expecting the data
flow.
2. DR might be expecting the data flow (for instance because of some
previous application layer signaling) but does not know the IP
address of the Data Sender DS.
For the second case, Figure 6 illustrates a possible attack: an
adversary Mallory M could be sniffing the application layer signaling
and thus knows the address and port number where DR is expecting the
data flow. Thus it could pretend to be DS and send a CREATE message
towards DR with the data flow description (M -> DR). Since DR does
not know the IP address of DS, it is not able to recognize that the
request is coming from the "wrong guy". It will send a success
RESPONSE message back and the middlebox will install policy rules
that will allow Mallory M to inject its data into the network.
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 8]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
Application Layer signaling
<------------------------------------>
/ \
/ +-----------------\------------+
/ | \ |
+-----+ +-----+ +-----+ |
| DS | -> | FW | | DR | |
+-----+ / +-----+ +-----+ |
CREATE / | |
+-----+ / +-------------------------------+
| M |----------
+-----+
Figure 6: DR behind a firewall with an adversary
Network administrators will probably not rely on a DR to check the IP
address of the DS. Thus we have to assume the worst case with an
attack such as in Figure 6. Many operators might not allow NSIS
signaling message to traverse the firewall in Figure 6 without proper
authorization. In this case the threat is not applicable.
SECURITY REQUIREMENT: A binding between the application layer and the
NSIS signaling SHOULD be provided.
3.4 Data Receiver (DR) behind a NAT
We will describe briefly the NSIS message flow that takes place to
install the necessary rules for the traversal of a data flow from DS
towards DR. For detailed description please refer to [1] Section
3.3.
DR sends a RESERVE-EXTERNAL-ADDRESS (REA) message to get a public
reachable address that can be used by potential DSs. The NAT
reserves an external address and port number and sends them back to
DR. The NAT adds an address mapping entry in its reservation list
which links the public and private addresses as follows:
(DR_ext <=> DR_int) (*).
The NAT sends a RESPONSE message with 'return external address'
object back to the DR with the address DR_ext. DR informs DS about
the public address that it has recently received, for instance, by
means of application layer signaling.
Now DS sends the CREATE message towards DR_ext. When the 'create
session' message arrives at the NAT, the NAT looks up its reservation
list and finds the entry (*).
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 9]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
Now the NAT knows the address of DS and stores it as a part of the
policy rule to be loaded. It forwards the message towards DR and
waits for the confirmation with the success RESPONSE message.
At the arrival of the success RESPONSE message from DR, the NAT
installs the policy rule to forward the data flow correctly from DS
to DR.
Possible attack:
We assume that the adversary obtains the external address allocated
at the NAT (possibly by eavesdropping on the application layer
signaling) and triggers the CREATE message before the NAT binding
expires. The CREATE message is assumed to travel from DS to DR
through NAT. An attacker Mallory M could send a CREATE message to
install a NAT binding to forward the data flow from M to DR instead
of from DS to DR. This kind of attack is equivalent to the attack
described in Section 3.3 above.
In order for this attack to work the following pre-requisities need
to hold:
The adversary needs to be authorized to create a NAT binding at
the NAT.
The adversary needs to know when a DR creates a NAT binding at the
DR. A certain timing is required and some specific information,
such as the message routing identifier and session identifier must
be known
Application Layer signaling
<------------------------------------>
/ \
/ +-----------------\------------+
/ | REA \ |
+-----+ +-----+ <----------- +-----+ |
| DS | -> | NAT | -----------> | DR | |
+-----+ / +-----+ rtn_ext_addr +-----+ |
CREATE / | |
+-----+ / +-------------------------------+
| M |----------
+-----+
Figure 7: DR behind a NAT with an adversary
SECURITY REQUIREMENT: TBD
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 10]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
3.5 NSLP message injection
Malicious Hosts, locate either off-path or on-path, could inject
arbitrary NATFW NSLP messages into the signaling path, causing
several problems. These problems apply when no proper authorization
and authentication scheme is available.
By injecting a bogus CREATE message with lifetime set to zero, a
malicious host could try to teardown NATFW NSLP session state
partially or completely on a data path, causing a service
interruption.
By injecting a bogus responses message, for instance, timeout, a
malicious host could try to teardown NATFW NSLP session state as
well. This could affect the data path partially or complete, causing
a service interruption.
Other messages, such as TRIGGER, can be misused by malicious hosts,
causing a service interruption. Following versions of this document
will investigate the impact of these messages as well.
4. Denial-of-Service Attacks
In this section we describe several ways how an adversary could
launch a Denial of service (DoS) attack on networks running NSIS for
middlebox configuration to exhaust their resources.
4.1 Flooding with CREATE messages from outside
4.1.1 Attacks due to NSLP state
A CREATE message requests the NSLP to store some state information
such as Session-ID and flow identifier.
The policy rules requested in the CREATE message will be installed at
the arrival of a confirmation from the Data Receiver with a success
RESPONSE message. The success RESPONSE message includes the session
ID. So the NSLP looks up the NSIS session and installs the requested
policy rules.
An adversary from outside could launch a DoS attack with arbitrary
CREATE messages. For each of these messages the middlebox needs to
store state information such as the policy rules to be loaded, i.e.,
the middlebox could run out of memory. This kind of attack is also
mentioned in [2] Section 4.8.
SECURITY REQUIREMENT: A NAT/FW NSLP node MUST authorize the
'create-session' message before storing state information.
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 11]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
4.1.2 Attacks due to authentication complexity
This kind of attack is possible if authentication is based on
mechanisms that require computing power, for example, digital
signatures.
For a more detailed treatment of this kind of attack, the reader is
encouraged to see [2].
SECURITY REQUIREMENT: A NAT/FW NSLP node MUST NOT introduce new
denial of service attacks based on authentication or key management
mechanisms.
4.1.3 Attacks to the endpoints
The NATFW NSLP requires firewalls to forward NSLP messages, a
malicious node may keep sending NSLP messages to a target. This may
consume the access network resources of the victim, drain the battery
of the victim's terminal and may force the victim to pay for the
received although undesired data.
This threat may be more particularly be relevant in networks where
access link is a limited resource, for instance in cellular networks,
and where the terminal capacities are limited.
SECURITY REQUIREMENT: A NATFW NSLP aware firewall or NAT MUST be able
to block unauthorized signaling message, if this threat is a concern.
4.1.4 Attacks to the NTLP
Flooding a middlebox with CREATE messages affects also the NTLP.
The success RESPONSE message needs to take the same route as the
previous CREATE message. Thus the NTLP needs to store routing
information for each CREATE message. This kind of attack is also
described in [2] Section 4.8.
SECURITY REQUIREMENT: A NAT/FW NSLP node MUST NOT introduce new
denial of service attacks based on authentication or key management
mechanisms.
4.2 Flooding with REA messages from inside
Although we are more concerned with possible attacks from outside the
network, we need also to consider possible attacks from inside the
network.
An adversary inside the network could send arbitrary
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 12]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
RESERVE-EXTERNAL-ADDRESS messages. At a certain point the NAT will
run out of port numbers and the access for other users to the outside
will be disabled.
SECURITY REQUIREMENT: The NAT/FW NSLP node MUST authorize state
creation for the RESERVE-EXTERNAL-ADDRESS message. Furthermore, the
NAT/FW NSLP implementation MUST prevent denial of service attacks
involving the allocation of an arbitrary number of NAT bindings or
the installation of a large number of packet filters.
5. Man-in-the-Middle Attacks
Figure 8 illustrates a possible man-in-the-middle attack using the
'reserve external address' (REA) message. This message travels from
DR towards the public Internet. The message might not be intercepted
by any NAT either because there are no NATs or because there are NSIS
unaware.
Mallory M returns a faked RESPONSE message with an IP address of its
choosing. This IP address is meant to be used by the DR as the
public external IP address. Malory might insert it own IP address in
the response, the IP address of a third party or the address of a
black hole. In the first case, the DR thinks that the address of
Mallory M is its public address and will inform the DS about it. As
a consequence, the DS will send the data traffic to Mallory M.
The data traffic from the DS to the DR will re-directed to Mallory M.
Mallory M will be able to read, modify or block the data traffic.
Eavesdropping and modification is only possible if the data traffic
is itself unprotected.
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 13]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
+-----+ +-----+ +-----+ +-----+
| DS | | M | | FW | | DR |
+-----+ +-----+ +-----+ +-----+
| | | |
| | REA | REA |
| | <------------------ | <------------ |
| | | |
| | ret_ext_addr | ret_ext_addr |
| | ------------------> | ------------> |
| | | |
| data traffic | | |
|===============>| data traffic |
| |===================================> |
Figure 8: MITM attack using the RESERVE-EXTERNAL-ADDRESS message
Please note that the NSIS aware firewall in Figure 8 might not be
present when DR communicates directly with the adversary.
SECURITY REQUIREMENT: Mutual authentication between neighboring NATFW
NSLP MUST be provided. To ensure that only legitimate nodes along
the path act as NSIS entities the initiator MUST authorize the
responder. In the example in Figure 8 the firewall FW must perform
an authorization with the neighboring entities.
6. Message Modification
Any on-path subverted node en route to the destination could easily
modify, inject or just drop an NSIS message. It could also hijack or
disrupt the communication.
SECURITY REQUIREMENT: Message integrity, replay protection and data
origin authentication between neighboring NAT/FW NSLPs MUST be
provided.
Message modification by a subverted NSIS node could create arbitrary
pinholes or NAT bindigs. For example:
o NATs need to modify the source/destination of the data flow in the
'create session' message.
o Each middlebox along the path may change the requested lifetime in
the CREATE message to fit their needs and/or local policy (see
also section 3.2.7 of [1] with regard to calculation of refresh
interval).
SECURITY REQUIREMENT: None. Malicous NSIS NATs and Firewalls will
not be addressed.
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 14]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
7. Session Modification/Deletion
The Session ID is included in signaling messages as a reference to
the established state. If an adversary is able to obtain the Session
Identifier for example by eavesdropping on signaling messages, it
would be able to add the same Session Identifier to a new a signaling
message and effect some modifications.
Consider the scenario described in Figure 9. Here an adversary
pretends to be 'DS in mobility'. The signaling messages start from
the DS and go through a series of routers towards the DR. We assume
that an off-path adversary is connected to one of the routers along
the old path (here Router 3). We also assume that the adversary
knows the Session ID of the NSIS session initiated by the DS.
Knowing the Session ID, the adversary now sends signalling messages
towards the DR. When the signaling message reaches Router3 then
existing state information can be modified or even deleted. The
adversary can modify or delete the established reservation causing
unexpected behavior for the legitimate user. The source of the
problem is that the Router 3 (cross-over router) is unable to decide
whether the new signaling message was initiated from the owner of the
session. In this scenario, the adversary need not even be located in
the DS-DR path. This problem and the solution approaches are
described in more detail in [6].
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 15]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
Session ID(SID-x)
+--------+ +--------+
+-------->--------+ Router +-------->+ DR |
Session ID(SID-x)| | 4 | | |
+---+----+ +--------+ +--------+
| Router |
+------+ 3 +*******
| +---+----+ *
| *
| Session ID(SID-x) * Session ID(SID-x)
+---+----+ +---+----+
| Access | | Access |
| Router | | Router |
| 1 | | 2 |
+---+----+ +---+----+
| *
| Session ID(SID-x) * Session ID(SID-x)
+----+------+ +----+------+
| DS | | Adversary |
| | | |
+-----------+ +-----------+
Figure 9: State Modification by off-path adversary
Summary: Off-path adversary's knowledge of Session-ID could cause
session modification/deletion.
SECURITY REQUIREMENT: TBD: This is not a NAT/FW NSLP specific problem
but a GIMPS problem. The initiator MUST be able to demonstrate
ownership of the session it wishes to modify.
7.1 Misuse of mobility in NAT handling
Another kind of session modification is related to mobility
scenarios. NSIS allows end hosts to be mobile it is possible that an
NSIS node behind a NAT needs to update its NAT binding in case of
address change. Whenever a host behind a NAT initiates a data
transfer, it is assigned an external IP and port number. In typical
mobility scenarios, the DR might also obtain a new address according
to the topology and it should convey the NAT binding updates. The
NAT is assumed to modify these NAT bindings based on the new IP
address conveyed by the endhost.
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 16]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
Public Private Address
Internet space
+----------+ +----------+
+----------| NAT |------------------|End host |
| | | |
+----------+ +----------+
|
|
| +----------+
\--------------------|Malicious |
|End host |
+----------+
data traffic
<========================
Figure 10: Misuse of mobility in NAT binding
For this description , we assume that a NAT binding state can be
changed with the help of NSIS signalling. When the DR is receiving
data traffic, if it happens to move to a new location, it sends an
NSIS signalling message to modify the NAT binding. It would use the
Session-ID and the new flow-id to update the state. The NAT updates
the binding and the DR continues to receive the data traffic.
Consider the scenario in Figure 10 where an the endhost(DR) and the
adversary are behind a NAT. The adversary pretending that it is the
end host could generate a spurious signaling message to update the
state at the NAT. This could be done for these purposes:
1. Connection hijacking by redirecting packets to the attacker as in
Figure 11
2. Third party flooding by redirecting packets to arbitrary hosts
3. Service disruption by redirecting to non-existing hosts
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 17]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
+----------+ +----------+ +----------+
| NAT | |End host | |Malicious |
| | | | |End host |
+----------+ +----------+ +----------+
| | |
| | |
| Data Traffic | |
|--------->----------| |
| | |
| | Spurious |
| | NAT binding update |
|---------<----------+--------<------------|
| | |
| | |
| Data Traffic | |
|--------->----------+-------->------------|
| | |
| | |
| | |
Figure 11: Connection Hijacking
SECURITY REQUIREMENT: A NAT/FW signaling message MUST be
authenticated, authorized, integrity protected and replay protected
between neighboring NAT/FW NSLP nodes.
8. Misuse of unreleased sessions
Assume that DS (N1) initiates NSIS session with DR (N2) through a
series of middleboxes as in Figure 12. When the DS is sending data
to DR, it might happen that the DR disconnects from the network
(crashes or moves out of the network in mobility scenarios). In such
cases, it is possible that another node N3 (which recently entered
the network protected by the same firewall) is assigned the same IP
address that was previously allocated to N2. The DS could take
advantage of the firewall policies installed already, if the refresh
interval time is very high. The DS can flood the node (N3), which
will consume the access network resources of the victim forcing it to
pay for unwanted traffic as shown in Figure 13.
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 18]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
Public Internet
+--------------------------+
| |
| |
+-------+ CREATE +---+-----+ +-------+ |
| |-------------->------| |---->---| | |
| N1 |--------------<------| FW |----<---| N2 | |
| | success RESPONSE | | | | |
| |==============>======| |====>===| | |
+-------+ Data Traffic +---+-----+ +-------+ |
| |
| |
+--------------------------+
Figure 12: Before mobility
Public Internet
+--------------------------+
| |
| |
+-------+ +---+-----+ +-------+ |
| | | | | | |
| N1 |==============>======| FW |====>===| N3 | |
| | Data Traffic | | | | |
| | | | | | |
+-------+ +---+-----+ +-------+ |
| |
| |
+--------------------------+
Figure 13: After mobility
Also, this threat is valid for the other direction as well. The DS
which is communicating with the DR may disconnect from the network
and this IP address may be assigned to a new node that had recently
entered the network. This new node could pretend to be the DS and
send data traffic to the DR in conformance with the firewall policies
and cause service disruption.
SECURITY REQUIREMENT: Data origin authentication is needed to
mitigate this threat. However, the described threat is applicable
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 19]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
only for the time until the policy rules are deleted due to NSLP soft
state. Awareness for this threat is important especially when the
refresh interval time is high. It should be noted, that networks
supporting mobility should remove any state at middleboxes when a
mobile node is diconnecting, thus leaving a clean state.
9. Data traffic injection
This attack takes place where there exists trust relationship between
machines. It is common in corporate networks, where internal
machines trust each other and authentication is only based on IP
address. Hence by spoofing a connection, an attacker is able to
reach the target machines, using the existing firewall rules.
The adversary is able to inject its own data traffic in conformance
with the firewall policies simultaneously along with the genuine DS.
SECURITY REQUIREMENT: Since IP spoofing is a general limitation of
non-cryptographic packet filters no security requirement needs to be
created for the NAT/FW NSLP. Techniques such as ingress filtering
(described below) and data origin authentication (such as provided
with IPsec based VPNs) can help mitigate this threat. This issue is,
however, outside the scope of this document.
Ingress Filtering: Consider the scenario shown in Figure 14. In this
scenario the DS is behind a router (R1) and a malicious node (M) is
behind another router (R2). The DS communicates with the DR through
a firewall (FW). The DS initiates NSIS signaling and installs
firewall policies at FW. But the malicious node is also able to send
data traffic using DS's source address. If R2 implements ingress
filtering, these spoofed packets will be blocked. But this ingress
filtering may not work in all scenarios. If both the DS and the
malicious node are behind the same router, then the ingress filter
will not be able to detect the spoofed packets as both the DS and the
malicious node are in the same address range.
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 20]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
+-----------------------------------+
| +------------------+ |
| | | |
| | | |
| | +-------+ +---+---+ |
| | | DS +>--+ R1 +->+ |
| | | | | | | |
| | +-------+ +---+---+ | |
| | | v |
| | | | |
| +------------------+ | +---+---+ +-------+
| | | | | |
| +---+ FW +-->--| DR |
| +------------------+ | | | |
| | | ****| |*****| |
| | | * +---+---+ +-------+
| | +-------+ +---+---+ * |
| | | M | | R2 | * |
| | | |***| |*** |
| | +-------+ +---+---+ |
| | | |
| | | |
| +------------------+ |
+-----------------------------------+
---->---- = genuine data traffic
********* = spoofed data traffic
Figure 14: Ingress filtering
10. Eavesdropping and traffic analysis
By collecting NSLP messages, an adversary is able to learn policy
rules for packet filters and knows which ports are open. It can use
this to inject its own data traffic due to the IP spoofing capability
as already mentioned in Section 9.
An adversary could learn authorization tokens included in CREATE
messages and use them to launch reply-attacks or to create a session
with its own address as source address. (cut-and-paste attack)
As shown in Section 4.3 of [6] a solution of Section 7 might require
confidentiality protection of signaling messages
SECURITY REQUIREMENT: The threat of eavesdropping itself does not
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 21]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
mandate the usage of confidentiality protection since an adversary
can also eavesdrop on data traffic. In the context of a particular
security solutions (e.g., authorization tokens) it might be necessary
to offer confidentiality protection. Confidentiality protection also
needs to be offered to the refresh period.
11. Conclusions
This memo describes security threads that are applicable to the NSIS
NATFW NSLP and some related threads inherent to firewalls and NATs.
Security requirements are given for the scenarios and some issues to
be considered in NTLP design are raised.
The most security threads shown here are related to missing
authentication or authorization schemes between all NATFW nodes.
Given a proper authentication and authorization scheme, many of these
threads can be mitigated. The general problem is the missing
identity of the nodes to what authorization and authentication could
be bound. IP addresses are in general not suitable, since NATs are
involved in any place to imagine and in mobility scenarios they are
changed frequently. Other attacks, such as message eavesdropping,
can be managed easily between adjacent NSIS nodes if the NTLP or NSLP
supports encryption. The flooding, or denial of service, of NSIS
nodes can be mitigated not only by authorization and authentication
schemes, but also by extensions to NATFW NSLP, where NSIS receivers
should be able to communicate upstream which type or from which node,
via the flow routing information, signaling traffic is allowed to be
forwarded to them.
12. Security Considerations
The entire document highlights security threats that need to be
mitigated for the NATFW NSLP. It also addresses security issues
related to packet filters. Security requirements have been derived
from the relevant threats.
13. Acknowledgments
This document is the result of discussions with many individuals.
The authors would like to thank especially: Marcus Brunner, Miquel
Martin, Frank Le, Joao Girao, and Elwyn Davis.
14. References
14.1 Normative References
[1] Stiemerling, M., Tschofenig, H. and M. Martin, "A NAT/Firewall
NSIS Signaling Layer Protocol (NSLP)",
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 22]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
draft-ietf-nsis-nslp-natfw-03 (work in progress), July 2004,
<reference.I-D.ietf-nsis-nslp-natfw.xml>.
[2] Tschofenig, H. and D. Kroeselberg, "Security Threats for NSIS",
draft-ietf-nsis-threats-05 (work in progress), June 2004,
<reference.I-D.ietf-nsis-threats.xml>.
[3] Schulzrinne, H. and R. Hancock, "GIMPS: General Internet
Messaging Protocol for Signaling", draft-draft-ietf-nsis-ntlp-02
(work in progress), May 2004,
<reference.I-D.draft-ietf-nsis-ntlp.xml>.
[4] Brunner, M., "Requirements for Signaling Protocols", RFC 3726,
April 2004, <reference.I-D.ietf-nsis-.requirements.xml>.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", March 1997.
14.2 Informative References
[6] Tschofenig, H., Schulzrinne, H., Hancock, R., McDonald, A. and
X. Fu, "Security Implications of the Session Identifier", June
2003, <reference.I-D.tschofenig-nsis-sid.xml>.
[7] Aoun, C., Brunner, M., Stiemerling, M., Martin, M. and H.
Tschofenig, "NAT/Firewall NSLP Migration Considerations",
draft-aoun-nsis-nslp-natfw-migration-01 (work in progress),
February 2004,
<reference.I-D.aoun-nsis-nslp-natfw-migration.xml>.
[8] Bless, R., "Mobility and Internet Signaling Protocols",
draft-manyfolks-signaling-protocol-mobility-00 (work in
progress), January 2004,
<reference.I-D.manyfolks-signaling-protocol-mobility.xml>.
[9] Bosch, S., "NSLP for Quality-of-Service signaling",
draft-ietf-nsis-qos-nslp-03 (work in progress), May 2004,
<reference.I-D.ietf-nsis-qos-nslp.xml>.
Authors' Addresses
Ali Fessi
Network Laboratories, NEC Europe Ltd.
EMail: alifessi@web.de
URI:
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 23]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
Martin Stiemerling
Network Laboratories, NEC Europe Ltd.
Kurfuersten-Anlage 36
Heidelberg 69115
Germany
Phone: +49 (0) 6221 905 11 13
EMail: stiemerling@netlab.nec.de
URI:
Srinath Thiruvengadam
Siemens
Otto-Hahn-Ring 6
Munich, Bayern 81739
Germany
EMail: srinath@mytum.de
Hannes Tschofenig
Siemens
Otto-Hahn-Ring 6
Munich, Bayern 81739
Germany
EMail: Hannes.Tschofenig@siemens.com
Cedric Aoun
Nortel Networks
France
EMail: cedric.aoun@nortelnetworks.com
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 24]
Internet-Draft Security Threats for the NAT/Firewall NSLP July 2004
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Fessi, et al. draft-fessi-nsis-natfw-threats-01.txt [Page 25]