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Certain versions of the software for the Cisco PIX 500 Series Security Appliances, the Cisco ASA 5500 Series Adaptive Security Appliances (ASA), and the Firewall Services Module (FWSM) are affected by a software bug that may cause the EXEC password, passwords of locally defined usernames, and the enable password in the startup configuration to be changed without user intervention.
Unauthorized users can take advantage of this bug to try to gain access to a device that has been reloaded after passwords in its startup configuration have been changed. In addition, authorized users can be locked out and lose the ability to manage the affected device.
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-20060823-firewall.
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Cisco PIX 500 Series Security Appliances, the Cisco ASA 5500 Series Adaptive Security Appliances, and the Firewall Services Module (FWSM) for the Cisco Catalyst 6500 Switches and Cisco 7600 Series Routers are impacted if they are running an affected software version.
Vulnerable Products
The PIX 500 Series Security Appliances and the ASA 5500 Series Adaptive Security Appliances are affected when running any of the following software versions:
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Any version (including interim versions) in the 7.0(x) train up to
and including 7.0(5)
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Any version (including interim versions) in the 7.1(x) train up to
and including 7.1(2.4)
The FWSM for the Cisco Catalyst 6500 Switches and Cisco 7600 Series Routers is affected when running the following software version:
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Any version (including interim versions) in the 3.1(x) train up to
and including 3.1(1.6)
Products Confirmed Not Vulnerable
The PIX 500 Series Security Appliances and the ASA 5500 Series Adaptive Security Appliances are not affected when running any of the following software versions:
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Any pre-7.x version (PIX only since the ASA does not run pre-7.x
code)
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7.2(1) and later
The FWSM for the Cisco Catalyst 6500 Switches and Cisco 7600 Series Routers is not affected when running any of the following software versions:
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Any 1.x and 2.x version
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3.1(2) and later
No other Cisco products are currently known to be affected by this issue.
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Any version (including interim versions) in the 7.0(x) train up to
and including 7.0(5)
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The Cisco PIX 500 Series Security Appliances, the Cisco ASA 5500 Series Adaptive Security Appliances, and the Firewall Services Module (FWSM) for the Cisco Catalyst 6500 Switches and Cisco 7600 Series Routers are part of Cisco's security portfolio. All of these products offer firewall services with stateful packet filtering and deep packet inspection. The PIX and ASA devices also offer other services like Virtual Private Networking (VPN), Content Filtering, and Intrusion Prevention.
On these devices, authentication for both EXEC mode and enable mode can be performed based on Authentication, Authorization, and Accounting (AAA) methods (Remote Authentication Dial-In User Service [RADIUS], Terminal Access Controller Access Control System Plus [TACACS+], or LOCAL). If a device does not have any AAA method (i.e., RADIUS, TACACS+, or LOCAL) configured, authentication for EXEC mode is performed using the password configured with the passwd command, and authentication for enable mode is performed using the password configured with the enable password command.
A software bug exists in certain versions of the software used by these devices that may cause, under some circumstances, the EXEC password, passwords of locally defined users, and the enable password that are stored in the startup configuration to be changed without user intervention. The startup configuration is stored in a non-volatile medium such as flash memory.
The affected passwords are set using the following configuration commands:
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passwd - configures the EXEC password.
For example:
pix(config)# passwd xxxxxxxxx
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username - configures local users and
their associated passwords. For example:
pix(config)# username admin password xxxxxxxx
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enable password - configures the password
used to enter enable mode. For example:
pix(config)# enable password xxxxxxxx
The software bug is known to be triggered in only two scenarios:
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A software crash, normally caused by a software bug. Please note
that not all software crashes may cause the undesired results discussed
above.
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Two or more users making concurrent configuration changes on a
device, regardless of the method (command-line interface [CLI], Adaptive
Security Device Manager [ASDM], Firewall Management Center, etc.) used to
access the device.
Please note that the passwords in the startup configuration will be changed when the configuration is saved, to the non-volatile medium where the startup configuration is stored, via the write memory or copy running-config startup-config commands. During normal operation, if the running configuration is not saved, passwords in the startup configuration will not change.
Once the passwords in the startup configuration are changed, administrators will be locked out after the next device reload if authentication for EXEC and for enable privilege depends on the passwords or local accounts stored in the startup configuration. If a AAA server (RADIUS or TACACS+) is used for authentication, the change of passwords in the startup configuration will only cause the undesired results when the AAA server is unavailable, regardless of whether the "LOCAL" authentication method is configured as a fallback, e.g. aaa authentication enable console RADIUS LOCAL.
Passwords are changed to a non-random value. This behavior is not due to a hardcoded default password or other explicitly induced set of password values, but rather the result of a coding error related to configuration parsing.
Devices configured in multiple context mode are also affected by this software bug.
This issue is documented in the following Cisco bug IDs:
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CSCse02703
(
registered customers only)
for the PIX and ASA devices
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CSCsd81487
(
registered customers only)
for the FWSM
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passwd - configures the EXEC password.
For example:
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Configuring authentication against an external RADIUS/TACACS+ server, per network security best practices, mitigates this issue. For information on how to configure authentication, please visit the following URLs:
PIX/ASA: http://www.cisco.com/en/US/products/ps6120/products_configuration_guide_chapter09186a00804512a5.html
If the passwords in the startup configuration have been modified as a result of software crash or concurrent configuration update, the administrators will need to perform a password recovery procedure, unless external AAA authentication is configured.
The password recovery procedure for the PIX and the ASA is documented at the following URL:
The password recovery procedure for the FWSM is documented at the following URL:
In addition, it is possible to limit the exposure of the firewall device by permitting remote connections only from known, trusted IP addresses. This is accomplished via the ssh, telnet, and http commands for Secure Shell (SSH), Telnet, and Secure Hyper-Text Transfer Protocol (HTTPS) access, respectively. For additional information on this, please refer to the "Managing System Access" section of the Cisco Security Appliance CLI Configuration Guide, available at:
http://www.cisco.com/en/US/products/ps6120/products_configuration_guide_chapter09186a0080450d39.html
In the case of the FWSM, please note that remote access to it can also be obtained via the Cisco Catalyst 6500 switch or Cisco 7600 Series router that hosts the FWSM blade. For this reason, the switch or router needs to be configured, using access control lists, to permit remote connections only from known, trusted IP addresses.
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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.
For version 7.0.x of the PIX/ASA software, the first fixed release is 7.0(5.1). The latest 7.0.x release for the PIX can be downloaded from:
http://www.cisco.com/pcgi-bin/tablebuild.pl/pix?psrtdcat20e2 ( registered customers only)
The latest 7.0.x release for the ASA can be downloaded from:
http://www.cisco.com/pcgi-bin/tablebuild.pl/asa?psrtdcat20e2 ( registered customers only)
For version 7.1.x of the PIX/ASA software, the first fixed release is 7.1(2.5). The latest 7.1.x interim for the PIX can be downloaded from:
http://www.cisco.com/pcgi-bin/tablebuild.pl/pix-interim?psrtdcat20e2 ( registered customers only)
The latest 7.1.x interim for the ASA can be downloaded from:
http://www.cisco.com/pcgi-bin/tablebuild.pl/asa-interim?psrtdcat20e2 ( registered customers only)
The first fixed release of the FWSM is 3.1(2). The latest 3.1 release of the FWSM software can be downloaded from:
http://www.cisco.com/pcgi-bin/tablebuild.pl/cat6000-fwsm?psrtdcat20e2 ( registered customers only)
Note: Interim images are not fully regression tested. Each individual fix has been unit tested, and the image has had a limited amount of automated regression testing to confirm a baseline of functionality. Keep this testing status in mind if you decide to run them in a production environment. We strongly encourage you to upgrade to a fully tested Maintenance or Feature release when it becomes available.
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The Cisco PSIRT is not aware of any public announcements or malicious use of the issue described in this advisory, although we are aware that some customers have been impacted by this software bug.
This issue was brought to Cisco's attention by Terje Bless from Helse Nord IKT. Cisco would like to thank him for working with us towards coordinated disclosure of this issue.
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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.
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Revision 1.0
2006-August-23
Initial public release.
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