Cisco Security Advisory
Multiple Vulnerabilities in Firewall Services Module
-
Multiple vulnerabilities exist in the Cisco Firewall Services Module (FWSM). These vulnerabilities occur in the processing of specific Hypertext Transfer Protocol (HTTP), Secure HTTP (HTTPS), Session Initiation Protocol (SIP), and Simple Network Management Protocol (SNMP) traffic. If verbose logging is enabled for debugging purposes, a vulnerability exists when the FWSM processes packets destined to itself. All of these vulnerabilities may result in a reload of the device.
An additional vulnerability is included in this advisory in which the manipulation of access control lists (ACLs) that make use of object groups may corrupt the ACL and create a situation where unwanted traffic may be permitted or desirable traffic may be blocked.
These vulnerabilities are independent of each other; a release that is affected by one vulnerability is not necessarily affected by the others.
There are workarounds for some of the vulnerabilities disclosed in this advisory.
Cisco has made free software available to address this issue for affected customers.
This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20070214-fwsm.
-
The vulnerabilities described in this document apply to the FWSM. The companion advisory https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20070214-pix 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
The following table indicates which software releases for the Cisco FWSM are affected and under what conditions:
Vulnerability Name
Only affected if...
Vulnerable by default?
Versions affected
Cisco Bug ID
1. Enhanced Inspection of Malformed HTTP Traffic May Cause Reload
Enhanced inspection of HTTP traffic is enabled through the command inspect http <appfw>
No
All 3.x software releases prior to 3.1(3.24)
2. Inspection of Malformed SIP Messages May Cause Reload
SIP inspection is enabled through the command fixup protocol sip <portnum> and/or fixup protocol sip udp <portnum> (in FWSM software 2.x and before) or through the command inspect sip (in FWSM software 3.x and later)
Yes
All software releases prior to 2.3(4.12) and all 3.x releases prior to 3.1(3.24)
3. Processing of Packets Destined to the FWSM May Cause Reload
Logging at "debugging" level (regardless of the logging destination) and syslog message 710006 is enabled
No
All 3.x software releases prior to 3.1(3.3)
4. Processing of Malformed HTTPS Traffic May Cause Reload
Network access authentication is enabled through the aaa authentication match or aaa authentication include commands
No
All 3.x software releases prior to 3.1(3.18)
5. Processing of Long HTTP Requests May Cause Reload
Network access authentication is enabled through the aaa authentication match or aaa authentication include commands
No
All 3.x releases prior to 3.1(2)
6. Processing HTTPS Traffic May Cause a Reload
HTTPS server is enabled through the http server enable command
No
All 3.x releases prior to 3.1(3.11)
7. Processing of Malformed SNMP Requests May Cause a Reload
SNMP traffic from a particular IP address is permitted through the command snmp-server host <interface name> <IP address of SNMP server>
No
All 3.x releases prior to 3.1(3.1)
8. Manipulation of ACL May Cause ACL Corruption
ACL makes use of object groups and ACL is manipulated by an administrator
No
All software releases prior to 2.3(4.7) and all 3.x releases prior to 3.1(3.1)
The relationship between the vulnerabilities described in this advisory and the equivalent vulnerabilities in the Cisco PIX 500 Series Security Appliances and Cisco ASA 5500 Series Adaptive Security Appliances is given in the following table. If a vulnerability discussed in this document is not present in this table, it does not affect the Cisco PIX 500 Series Security Appliances and Cisco ASA 5500 Series Adaptive Security Appliances.
Vulnerability
PIX/ASA Bug ID
FWSM Bug ID
Enhanced Inspection of Malformed HTTP Traffic May Cause Reload
Inspection of Malformed SIP Messages May Cause Reload
CSCse27708 and CSCsd97077
To determine if you are running a vulnerable version of FWSM software, issue the show module command in IOS or CatOS to identify what modules and sub-modules are installed in the system.
The example below shows a system with a Firewall Service Module (WS-SVC-FWM-1) installed in slot 4.
6506-B#show module Mod Ports Card Type Model Serial No. --- ----- -------------------------------------- ------------------ ----------- 1 48 SFM-capable 48 port 10/100/1000mb RJ45 WS-X6548-GE-TX SAxxxxxxxxx 4 6 Firewall Module WS-SVC-FWM-1 SAxxxxxxxxx 5 2 Supervisor Engine 720 (Active) WS-SUP720-BASE SAxxxxxxxxx 6 2 Supervisor Engine 720 (Hot) WS-SUP720-BASE SAxxxxxxxxx
After locating the correct slot, issue the show module
command to identify the version of software running: 6506-B#sho module 4 Mod Ports Card Type Model Serial No. --- ----- -------------------------------------- ------------------ ----------- 4 6 Firewall Module WS-SVC-FWM-1 SAxxxxxxxxx Mod MAC addresses Hw Fw Sw Status --- ---------------------------------- ------ ------------ ------------ ------- 4 0003.e4xx.xxxx to 0003.e4xx.xxxx 3.0 7.2(1) 2.3(1) Ok
In this example, the FWSM is running version 2.3(1) as indicated by the column under "Sw" above.
Note: recent versions of IOS will show the software version of each module in the output from the show module command so executing the show module
command is not necessary. Alternatively, the information may also be gained directly from the FWSM through the show version command:
FWSM#show version FWSM Firewall Version 2.3(1)
For customers managing their FWSM through the PIX Device Manager (PDM) or the Cisco Adaptive Security Device Manager (ASDM), log into the application, and the version may be found either in the table in the login window or in the upper left hand corner of the PDM/ASDM window indicated by a label similar to:
FWSM Version: 2.3(1)
Products Confirmed Not Vulnerable
With the exception of the Cisco PIX 500 Series Security Appliances and the Cisco ASA 5500 Series Adaptive Security Appliances, no other Cisco products are known to be vulnerable to the issues described in this advisory.
-
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
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:
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
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
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) .
-
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:
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
from the configuration, where appfw is the name of an HTTP map. For further information about the inspect http
command, and the type of checks it performs on HTTP traffic, please see the documentation for this command at: 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 earlier, it 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 globalIn 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
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 insidewill 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
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.
-
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).
Vulnerability
First Fixed Release
1. Enhanced Inspection of Malformed HTTP Traffic May Cause Reload (CSCsd75794)
3.1(3.24) (the 2.3.x series are not affected)
2. Inspection of Malformed SIP Messages May Cause Reload (CSCsg80915)
2.3(4.12) for the 2.3.x series, and 3.1(3.24) for the 3.x series
3. Processing of Packets Destined to the FWSM May Cause Reload (CSCse85707)
3.1(3.3) (the 2.3.x series are not affected)
4. Processing of Malformed HTTPS Requests May Cause Reload (CSCsg50228)
3.1(3.18) (the 2.3.x series are not affected)
5. Processing of Long HTTP Requests May Cause Reload (CSCsd91268)
3.1(1.9) (the 2.3.x series are not affected)
6. Processing HTTPS Traffic May Cause a Reload (CSCsf29974)
3.1(3.11) (the 2.3.x series are not affected)
7. Processing of Malformed SNMP Requests May Cause a Reload (CSCse52679)
3.1(3.1) (the 2.3.x series are not affected)
8. Manipulation of ACL May Cause ACL Corruption (CSCse60868) , (CSCse99740) and (CSCsd50667)
2.3(4.7) for the 2.3.x series, and 3.1(3.1) for the 3.x series
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
-
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.
-
To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
-
Show LessRevision 1.4
2007-Jun-20
Added information about CSCsd50667 - duplicate of CSCse99740 - to be consistent with the FWSM release notes.
Revision 1.3
2007-Feb-23
Clarify that the "Inspection of Malformed SIP Messages May Cause Reload" vulnerability affects SIP traffic over both TCP and UDP transport, and that a configuration may be affected for both, depending on the commands used. The workaround of disabling SIP may also require removing two commands.
Revision 1.2
2007-Feb-21
It was incorrectly stated in previous versions of this document that SIP inspection is disabled by default in FWSM 3.x software. The advisory has been revised to make it clear that the "Inspection of Malformed SIP Messages May Cause Reload" vulnerability affects the default configuration in both 2.x and 3.x software.
Revision 1.1
2007-Feb-14
Revised CVSS scores for CSCsd91268 (to reflect Remote Code Execution potential) and for CSCse60868 and CSCse99740 (to reflect that authentication is required).
Revision 1.0
2007-Feb-14
Initial public release.
-
THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
A stand-alone copy or paraphrase of the text of this document that omits the distribution URL is an uncontrolled copy, and may lack important information or contain factual errors. The information in this document is intended for end-users of Cisco products.