Summary

• A vulnerability in the implementation of the TACACS+ protocol in Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to view sensitive data or bypass authentication. 

  This vulnerability exists because the system does not properly check whether the required TACACS+ shared secret is configured. A machine-in-the-middle attacker could exploit this vulnerability by intercepting and reading unencrypted TACACS+ messages or impersonating the TACACS+ server and falsely accepting arbitrary authentication requests. A successful exploit could allow the attacker to view sensitive information in a TACACS+ message or bypass authentication and gain access to the affected device.  

  Cisco has released software updates that address this vulnerability. There are workarounds that address this vulnerability.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ios-tacacs-hdB7thJw

  This advisory is part of the September 2025 release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: September 2025 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco devices if they are running a vulnerable release of Cisco IOS and IOS XE Software and if they are configured to use TACACS+ but are missing the TACACS+ shared secret.

  For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.

  Determine the Device Configuration

  To determine whether a device has TACACS+ or TACACS+ server shared secrets configured, use the instructions in the following sections.

  Determine the TACACS+ Configuration

  To determine whether a device has TACACS+ configured, use the show running-config | include tacacs CLI command or the show running-config | section tacacs CLI command. If there is no output, the device is not affected by this vulnerability. If there is output, TACACS+ is configured, and the device may be affected.

  The following example shows the output for a device with Groups configured:

  Router# show running-config | include tacacs
  aaa group server tacacs+ ise1
  tacacs server ise

  The following example shows the output for a device without Groups configured:

  Router# show running-config | section tacacs
  address ipv4 10.1.1.1
  tacacs-server key cisco123
  Router#

  The following example shows the output for a device with server-private configured:

  Router# show running-config | section tacacs
  aaa group server tacacs+ ise
   server-private 10.1.1.1
  tacacs server ise
   address ipv4 10.1.1.1
   key Cisc0123

  Determine the TACACS+ Server Key Configuration

  To determine whether a device has TACACS+ server shared secrets configured, use the show running-config | include tacacs server|key CLI command. If every TACACS+ server that is configured has a shared secret configured, the device is not affected. If any TACACS+ server is configured without a shared key, the device is affected.

  The following example shows output from an affected device that has Groups configured, does not have Groups configured, or has server-private configured. Note the missing key line.

  Router# show running-config | include tacacs server|key
  tacacs server ise
  

  The following example shows output from a device that is not affected and that has Groups configured, does not have Groups configured, or has server-private configured. Note the key cisc0123 shared secret.

  Router# show running-config | include tacacs server|key
  tacacs server ise
   key cisco123

  Note: Every TACACS+ server must have the key configured to not be affected.

  The following example shows output from an affected device with multiple TACACS+ servers configured. Note the missing key line for ise2. 

  Router# show running-config | include tacacs server|key
  tacacs server ise1
   key cisco123
  tacacs server ise2

  The following example shows the output from an unaffected device with multiple TACACS+ servers configured. Note the key cisc0123 shared secret for both TACACS+ servers.

  Router# show running-config | include tacacs server|key
  tacacs server ise1
   key cisco123
  tacacs server ise2
   key cisco123
  

  The following example shows the output from an unaffected device with multiple TACACS+ servers that have a globally configured TACACS+ key. Note that the key cisc0123 shared secret is globally configured.

  Router# show running-config | include tacacs server|key
   tacacs server key 7 cisco123
  tacacs server ise1
  tacacs server ise2

  Products Confirmed Not Vulnerable

  Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.

  Cisco has confirmed that this vulnerability does not affect the following Cisco products:

  • IOS XR Software
  • NX-OS Software

Workarounds

• There is a workaround that addresses this vulnerability. Ensure every TACACS+ server that is configured on the device has a shared secret configured. 

  While this workaround has been deployed and was proven successful in a test environment, customers should determine the applicability and effectiveness in their own environment and under their own use conditions. Customers should be aware that any workaround or mitigation that is implemented may negatively impact the functionality or performance of their network based on intrinsic customer deployment scenarios and limitations. Customers should not deploy any workarounds or mitigations before first evaluating the applicability to their own environment and any impact to such environment.

Fixed Software

• Cisco considers any workarounds and mitigations to be temporary solutions until an upgrade to a fixed software release is available. To fully remediate this vulnerability and avoid future exposure as described in this advisory, Cisco strongly recommends that customers upgrade to the fixed software indicated in this advisory.

  Cisco IOS and IOS XE Software

  To help customers determine their exposure to vulnerabilities in Cisco IOS and IOS XE Software, Cisco provides the Cisco Software Checker. This tool identifies any Cisco security advisories that impact a specific software release and the earliest release that fixes the vulnerabilities that are described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities that are described in all the advisories that the Software Checker identifies (“Combined First Fixed”). 

  To use the tool, go to the Cisco Software Checker page and follow the instructions. Alternatively, use the following form to determine whether a release is affected by any Cisco Security Advisory. To use the form, follow these steps:

  1. Choose which advisories the tool will search—only this advisory, only advisories with a Critical or High Security Impact Rating (SIR), or all advisories.
  2. Enter a release number—for example, 15.9(3)M2 or 17.3.3.
  3. Click Check.

   

  Only this advisory All Critical and High advisories All advisories

   

Exploitation and Public Announcements

• The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.

Source

• This vulnerability was found during the resolution of a Cisco Technical Assistance Center (TAC) support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ios-tacacs-hdB7thJw

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2025-SEP-24

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