Summary

• A vulnerability in the RADIUS setting Reject RADIUS requests from clients with repeated failures on Cisco Identity Services Engine (ISE) could allow an unauthenticated, remote attacker to cause Cisco ISE to restart unexpectedly.

  This vulnerability is due to a logic error when processing a RADIUS access request for a MAC address that is already a rejected endpoint. An attacker could exploit this vulnerability by sending a specific sequence of multiple crafted RADIUS access request messages to Cisco ISE. A successful exploit could allow the attacker to cause a denial of service (DoS) condition when Cisco ISE restarts.

  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-ise-radsupress-dos-8YF3JThh

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco ISE releases 3.4.0, 3.4 Patch 1, 3.4 Patch 2, and 3.4 Patch 3, which have the Reject RADIUS requests from clients with repeated failures setting enabled by default.

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

  Determine the Device Configuration

  To determine if Reject RADIUS requests from clients with repeated failures is enabled, choose Administration > System > Settings > Protocols > RADIUS in the Cisco ISE web UI. Navigate to the Suppress Repeated Failed Clients and repeated accounting section. The check box that enables the setting should be checked because it is a default configuration.

  For more information on this feature, which is new in Cisco ISE Release 3.4.0, see RADIUS Settings in the Cisco Identity Services Engine Administrator Guide, Release 3.4.

  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 Cisco ISE Passive Identity Connector (ISE-PIC).

Workarounds

• Cisco ISE devices are affected by this vulnerability only if Reject RADIUS requests from clients with repeated failures is configured.
  
  As a workaround, administrators can disable this setting using the following steps:

  1. Choose Administration > System > Settings > Protocols > RADIUS.
  2. Navigate to the Suppress Repeated Failed Clients and repeated accounting section.
  3. Uncheck only the Reject RADIUS requests from clients with repeated failures check box.

  This setting is enabled by default and will be configured in most environments. If this configuration setting is disabled, the Cisco ISE device is not affected by this vulnerability. However, Cisco recommends re-enabling this configuration setting once the device has been upgraded to the fixed code.

  For more information on this feature, which is new in Cisco ISE Release 3.4.0, see RADIUS Settings in the Cisco Identity Services Engine Administrator Guide, Release 3.4.

  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.

  Fixed Releases

  Customers are advised to upgrade to an appropriate fixed software release as indicated in the following table:

  Cisco ISE Release	First Fixed Release
  3.3 and earlier	Not vulnerable
  3.4	3.4 Patch 4
  3.5	Not vulnerable

  For instructions on upgrading a device, see the Upgrade Guides on the Cisco Identity Service Engine support page.

  The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.

Exploitation and Public Announcements

• The Cisco 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-ise-radsupress-dos-8YF3JThh

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2025-NOV-05

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