Products & Services

The vulnerabilities described in this document apply to the FWSM. The companion advisory http://www.cisco.com/warp/public/707/cisco-sa-20070214-pix.shtml contains information about similar vulnerabilities that affect the Cisco PIX 500 Series Security Appliances and the Cisco ASA 5500 Series Adaptive Security Appliances.

Vulnerable Products

Products Confirmed Not Vulnerable

The Cisco Firewall Services Module is a high-speed, integrated firewall module for Catalyst 6500 series switches and Cisco 7600 series routers. It offers firewall services with stateful packet filtering and deep packet inspection.

Multiple vulnerabilities exist in certain versions of the FWSM software that may cause the device to unexpectedly reload or that may cause traffic to be permitted or denied contrary to the security policy in place.

1. Enhanced Inspection of Malformed HTTP Traffic May Cause Reload

This vulnerability may cause a FWSM to reload when the FWSM performs enhanced inspection of HTTP requests, and a malformed HTTP request is inspected by the FWSM. The FWSM only performs enhanced inspection of HTTP traffic when the command inspect http <appfw> is present in the configuration (appfw is the name of a specific HTTP map.) This command is disabled by default.

Note:  Enhanced inspection of HTTP traffic is what makes a configuration affected. Regular inspection of HTTP traffic (through the command inspect http without an HTTP map) will not make a configuration affected by this vulnerability.

For information on what enhanced inspection of HTTP traffic does, and how to configure it, please refer to the following URL:

http://www.cisco.com/en/US/products/hw/switches/ps708/products_module_configuration_guide_chapter09186a0080577c72.html#wp1390330

This vulnerability is documented in Cisco Bug ID CSCsd75794 ( registered customers only) .

2. Inspection of Malformed SIP Messages May Cause Reload

This vulnerability may cause a FWSM to reload when a malformed SIP message is received (over Transmission Control Protocol [TCP] or over User Datagram Protocol [UDP]) and deep packet inspection of SIP messages is enabled through the commands fixup protocol sip <portnum> for SIP over TCP and/or fixup protocol sip udp <portnum> for SIP over UDP (in FWSM software 2.3.x and before) or through the command inspect sip (in FWSM software 3.x and later). SIP fixup (in 2.x and earlier) and SIP inspection (in 3.x and later) are enabled by default.

This vulnerability is documented in Cisco Bug ID CSCsg80915 ( registered customers only) .

3. Processing of Packets Destined to the FWSM May Cause Reload

This vulnerability will cause the FWSM to reload when trying to generate syslog message 710006. For this to happen the following two conditions must be satisfied:

• The FWSM receives a packet for one of the device's IP addresses and the message is not one of the following protocols: TCP, UDP, ICMP, OSPF, Failover, PIM, IGMP, and ESP. The source of the packet is not relevant.
  
• Logging must be enabled at a level high enough to generate syslog message 710006. By default this is debugging level (level 7). Please note that logging is disabled by default, and Cisco recommends customers only log at debugging level for debugging and troubleshooting purposes.
  

  Note:  The documentation for the Cisco Security Monitoring, Analysis and Response System (CS-MARS) suggests logging at the debugging level so more events can be reported by the firewall.

For more information on syslog message 710006 please refer to the following document:

• Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Logging Configuration and System Log Messages, 3.1
  http://www.cisco.com/en/US/products/hw/switches/ps708/products_system_message_guide_chapter09186a00804d74bd.html#wp1285757
  

This vulnerability is documented in Cisco Bug ID CSCse85707 ( registered customers only) .

4. Processing of Malformed HTTPS Requests May Cause Reload

This vulnerability may cause the FWSM to reload when a user tries to access a web site and the network administrator has configured the device to authenticate users before granting them network access. This feature is known as "authentication for network access", or auth-proxy, and is enabled through the command aaa authentication match or aaa authentication include.

The reload is actually triggered by a specific HTTPS request that is invalid, and therefore, unlikely to be generated by a regular web browser.

This vulnerability is documented in Cisco Bug ID CSCsg50228 ( registered customers only) .

5. Processing of Long HTTP Requests May Cause Reload

This vulnerability may also cause the FWSM to reload when the administrator has enabled "authentication for network access ("auth-proxy") through the commands aaa authentication match or aaa authentication include. However, in this case, the HTTP request that causes the reload is valid, although it is not a normal request in the sense that the URL being requested is very long. A web browser could potentially generate such a request during regular browsing.

This vulnerability is documented in Cisco Bug ID CSCsd91268 ( registered customers only) .

6. Processing of HTTPS Traffic May Cause Reload

This vulnerability may cause a FWSM to reload when the FWSM receives a particular type of HTTPS traffic directed to the FWSM itself. This is only a concern when the HTTPS server on the FWSM is enabled through the command http server enable. This command is disabled by default.

Cisco is aware of a commercial vulnerability scanner that can generate the HTTPS traffic that triggers the reload. We are not aware of regular web browser traffic that triggers this bug.

This vulnerability is documented in Cisco Bug ID CSCsf29974 ( registered customers only) .

7. Processing of Malformed SNMP Requests May Cause a Reload

This vulnerability may cause a FWSM to reload upon receipt of a malformed SNMP message from a trusted device. The trusted device must be allowed explicit SNMP poll access via the command snmp-server host <interface name> <IP of trusted device>.

This vulnerability is documented in Cisco Bug IDs CSCse52679 ( registered customers only) .

8. Manipulation of ACL May Cause ACL Corruption

This vulnerability may cause access control entries (ACEs) in an ACL to be evaluated out of order, or not to be evaluated. This ACL corruption is manifested, besides the obvious traffic implications, when the output from the show access-list command and the corresponding ACL shown by the show running-config command appear to be out of sync. Only a manual reload of the device will cause this condition to go away.

The ACL corruption occurs when an ACL that makes use of object groups is manipulated.

This vulnerability is documented in Cisco Bug IDs CSCse60868 ( registered customers only) , CSCse99740 ( registered customers only) and CSCsd50667 ( registered customers only) .

Vulnerability Scoring Details

Cisco is providing scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS).

Cisco will provide a base and temporal score. Customers can then compute environmental scores to assist in determining the impact of the vulnerability in individual networks.

Cisco PSIRT will set the bias in all cases to normal. Customers are encouraged to apply the bias parameter when determining the environmental impact of a particular vulnerability.

CVSS is a standards based scoring method that conveys vulnerability severity and helps determine urgency and priority of response.

Cisco has provided an FAQ to answer additional questions regarding CVSS at http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html.

Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at http://intellishield.cisco.com/security/alertmanager/cvss.

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In all cases, with the exception of the "Manipulation of ACL May Cause ACL Corruption" vulnerability, successful exploitation of any vulnerability may cause a reload of the affected device. Repeated exploitation could result in a sustained Denial-of-Service (DoS) condition.

In the case of the "Processing of Long HTTP Requests May Cause Reload" vulnerability (CSCsd91268), the reload occurs because a stack-based buffer is overflowed. In this case remote code execution may be possible.

In the case of the "Manipulation of ACL May Cause ACL Corruption" vulnerability, a device that becomes affected after an administrator manipulates an ACL with object groups may allow traffic that would normally be denied, or would deny traffic that would normally be permitted. If the ACL is used for other functions like NAT (policy NAT and NAT exemption), AAA (auth-proxy), control of access to the device (SSH, Telnet, HTTP, ICMP), then those functions may be adversely affected as well.

When considering software upgrades, also consult http://www.cisco.com/go/psirt and any subsequent advisories to determine exposure and a complete upgrade solution.

In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco Technical Assistance Center ("TAC") or your contracted maintenance provider for assistance.

Each row of the FWSM software table (below) describes one of the vulnerabilities described in this document. For each vulnerability the earliest possible release that contains the fix (the "First Fixed Release") and the anticipated date of availability for each are listed in the "First Fixed Release" column. A device running a release that is earlier than the release in a specific column (less than the First Fixed Release) is known to be vulnerable. The release should be upgraded at least to the indicated release or a later version (greater than or equal to the First Fixed Release label).

For the 2.3.x series, FWSM software version 2.3(4.12) contains the fixes for all the vulnerabilities described in this document.

For the 3.x series, FWSM software version 3.1(4) contains the fixes for all the vulnerabilities described in this document.

FWSM software is available for download from the following location on cisco.com:

http://www.cisco.com/pcgi-bin/tablebuild.pl/cat6000-fwsm?psrtdcat20e2

For FWSM release 2.3(4.12) please use the following link:

http://www.cisco.com/pcgi-bin/tablebuild.pl/FWSMPSIRT?psrtdcat20e2

Additional mitigations that can be deployed on Cisco devices within the network are available in the Cisco Applied Mitigation Bulletin companion document for this advisory:

http://www.cisco.com/warp/public/707/cisco-amb-20070214-firewall.shtml

1. Enhanced Inspection of Malformed HTTP Traffic May Cause Reload

It is possible to mitigate this vulnerability by disabling enhanced inspection of HTTP traffic. Please note that disabling HTTP enhanced inspection will prevent the FWSM from protecting against specific attacks and other threats that may be associated with HTTP traffic. Enhanced inspection of HTTP traffic is disabled by removing the command inspect http <appfw> from the configuration, where appfw is the name of an HTTP map.

For further information about the inspect http <appfw> command, and the type of checks it performs on HTTP traffic, please see the documentation for this command at:

http://www.cisco.com/en/US/products/hw/switches/ps708/products_command_reference_chapter09186a008048e279.html#wp1570030

Please note that the command inspect http (without an HTTP map) can be left in the configuration and the device will not be affected by this vulnerability.

2. Inspection of Malformed SIP Messages May Cause Reload

It is possible to mitigate this vulnerability by disabling deep packet inspection ("fixup" in software version prior to 3.x or "inspect" in software version 3.x and later) of SIP messages. In FWSM software 2.x and is is necessary to use both no fixup protocol sip and no fixup protocol sip udp to stop deep packet inspection of SIP messages over TCP and UDP transport (in FWSM 3.x and later no inspect sip will stop deep packet inspection of SIP messages over both TCP and UDP.) Note, however, that this may have negative impact on devices terminating SIP sessions since SIP traffic will no longer undergo stateful application inspection, and devices which terminate sessions for this protocol will be exposed to packets that may cause these devices to crash or become compromised.

If you are running a 3.x FWSM software release, then the alternative is to allow traffic only from the trusted hosts. The configuration to accomplish this is as follows:

access-list sip-acl extended permit udp 10.1.1.0 255.255.255.0 host 192.168.5.4 eq sip
access-list sip-acl extended permit udp host 192.168.5.4 10.1.1.0 255.255.255.0 eq sip

class-map sip-traffic
 match access-list sip-acl
!
!
policy-map global_policy
 class inspection_default
  inspect dns maximum-length 512
  inspect ftp
  inspect h323 h225
  inspect h323 ras
  inspect rsh
  inspect rtsp
  inspect esmtp
  inspect sqlnet
  inspect skinny
  inspect sunrpc
  inspect xdmcp
  inspect netbios
  inspect tftp
 class sip-traffic
  inspect sip
!
service-policy global_policy global
      

In this example SIP endpoints are any host within 10.1.1.0 network (inside the trusted network) and a host with the IP address of 192.168.5.4 (outside of the trusted network). You would have to substitute these IP addresses with the ones that are used in your network.

Please note that SIP is an UDP-based protocol, so spoofing SIP messages is possible.

3. Processing of Packets Destined to the FWSM May Cause Reload

Since this vulnerability only manifests itself when syslog message 710006 is generated, it is possible to workaround the vulnerability either by disabling generation of syslog message 710006 altogether, or by logging at a syslog level that is lower than the syslog level at which this message is generated.

By default, syslog message 710006 is generated at syslog level 7 ("debugging"), so a viable workaround is to log at level 6 or lower. This can be accomplished with the command logging <destination> 6. If syslog message 710006 has been moved to a different logging level, then the logging level in use must be changed accordingly to prevent the message from being generated.

If logging at the "debugging" level is necessary, the vulnerability can also be eliminated by disabling this particular syslog message by using the command no logging message 710006.

4. Processing of Malformed HTTPS Requests May Cause Reload

There are no workarounds for this vulnerability.

5. Processing of Long HTTP Requests May Cause Reload

There are no workarounds for this vulnerability.

6. Processing HTTPS Traffic May Cause a Reload

Since this vulnerability is caused by the HTTPS server on the FWSM failing to handle certain types of HTTPS traffic, disabling the HTTPS server through the command no http server enable is a valid workaround if this functionality is not needed. Please note that this functionality is used by ASDM, so if configuration of the FWSM is exclusively done through ASDM disabling the HTTPS server may not be a viable workaround.

Additionally, it is possible to limit the exposure by allowing HTTPS connections only from trusted IP addresses or networks. This can be accomplished with the http command. For example, the following command:

	FWSM(config)# http 192.168.1.10 255.255.255.255 inside
      

will only permit HTTPS connections from the IP address 192.168.1.10.

7. Processing of Malformed SNMP Requests May Cause a Reload

This bug can only be triggered by a malformed SNMP message that comes from a device that is allowed SNMP access on the FWSM. If SNMP is not needed it can be removed through the command no snmp-server host <interface name> <IP address of trusted device>, which will eliminate the vulnerability.

8. Manipulation of ACL May Cause ACL Corruption

There are no workarounds for this vulnerability. However, please note that the ACL corruption does not occur during normal operation of the device and it cannot be triggered by some type of traffic. It can only occur if an administrator makes configuration changes (and more specifically, if an administrator manipulates an ACL.) For this reason, if ACL changes are made only during a maintenance window, and the FWSM is reloaded after making those changes, there should not be any concerns with this vulnerability.

Cisco will make free software available to address this vulnerability for affected customers. This advisory will be updated as fixed software becomes available. Prior to deploying software, customers should consult their maintenance provider or check the software for feature set compatibility and known issues specific to their environment.

Customers may only install and expect support for the feature sets they have purchased. By installing, downloading, accessing or otherwise using such software upgrades, customers agree to be bound by the terms of Cisco's software license terms found at http://www.cisco.com/public/sw-license-agreement.html, or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact either "psirt@cisco.com" or "security-alert@cisco.com" for software upgrades.

Customers with contracts should obtain upgraded software through their regular update channels. For most customers, this means that upgrades should be obtained through the Software Center on Cisco's worldwide website at http://www.cisco.com.

Customers whose Cisco products are provided or maintained through prior or existing agreement with third-party support organizations such as Cisco Partners, authorized resellers, or service providers should contact that support organization for guidance and assistance with the appropriate course of action in regards to this advisory.

The effectiveness of any workaround or fix is dependent on specific customer situations such as product mix, network topology, traffic behavior, and organizational mission. Due to the variety of affected products and releases, customers should consult with their service provider or support organization to ensure any applied workaround or fix is the most appropriate for use in the intended network before it is deployed.

Customers who purchase direct from Cisco but who do not hold a Cisco service contract and customers who purchase through third-party vendors but are unsuccessful at obtaining fixed software through their point of sale should get their upgrades by contacting the Cisco Technical Assistance Center (TAC). TAC contacts are as follows.

• +1 800 553 2447 (toll free from within North America)
  
• +1 408 526 7209 (toll call from anywhere in the world)
  
• e-mail: tac@cisco.com
  

Have your product serial number available and give the URL of this notice as evidence of your entitlement to a free upgrade. Free upgrades for non-contract customers must be requested through the TAC.

Refer to http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional TAC contact information, including special localized telephone numbers and instructions and e-mail addresses for use in various languages.

The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.

Some of these vulnerabilities where reported to Cisco by customers that experienced these issues during normal operation of their equipment. The other vulnerabilities were discovered during internal testing.

This advisory is posted on Cisco's worldwide website at :

http://www.cisco.com/warp/public/707/cisco-sa-20070214-fwsm.shtml

In addition to worldwide web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail and Usenet news recipients.

• cust-security-announce@cisco.com
  
• first-teams@first.org
  
• bugtraq@securityfocus.com
  
• vulnwatch@vulnwatch.org
  
• cisco@spot.colorado.edu
  
• cisco-nsp@puck.nether.net
  
• full-disclosure@lists.grok.org.uk
  
• comp.dcom.sys.cisco@newsgate.cisco.com
  

Future updates of this advisory, if any, will be placed on Cisco's worldwide website, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the above URL for any updates.

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Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's worldwide website at http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.