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medium threat

CVE-2026-41956: F5 TMM Termination Vulnerability on UDP Virtual Servers

CVE-2026-41956 describes a vulnerability in F5 Networks' Traffic Management Microkernel (TMM) where undisclosed requests can cause TMM termination when a classification profile is configured on a UDP virtual server, leading to a denial-of-service condition.

CVE-2026-41956 is a vulnerability affecting F5 Networks’ Traffic Management Microkernel (TMM). When a classification profile is configured on a UDP virtual server, specifically crafted requests can trigger a termination of the TMM process. This vulnerability leads to a denial-of-service condition, impacting the availability of services relying on the affected virtual server. The vulnerability is present in undisclosed versions of the software, excluding those that have reached End of Technical Support (EoTS). Exploitation does not require authentication.

Attack Chain

  1. An attacker identifies a target F5 device with a UDP virtual server configured with a classification profile.
  2. The attacker crafts a malicious UDP request specifically designed to trigger the vulnerability.
  3. The attacker sends the crafted UDP request to the vulnerable UDP virtual server.
  4. The F5 device processes the malicious UDP request through the configured classification profile.
  5. Due to the vulnerability, the Traffic Management Microkernel (TMM) encounters an unhandled exception.
  6. The TMM process terminates unexpectedly, leading to a denial-of-service condition.
  7. Services relying on the affected UDP virtual server become unavailable.

Impact

Successful exploitation of CVE-2026-41956 results in a denial-of-service condition. The termination of the Traffic Management Microkernel (TMM) disrupts traffic processing, causing the affected UDP virtual server and associated services to become unavailable. This can impact critical network functions, leading to service outages and potential financial losses.

Recommendation

  • Monitor network traffic for anomalous UDP packets targeting F5 devices, using the Detect Anomalous UDP Traffic Targeting F5 Devices Sigma rule to identify suspicious activity.
  • Apply the security patches or mitigations provided by F5 Networks as soon as they are available to address CVE-2026-41956.
  • Deploy the Detect TMM Process Termination Sigma rule to monitor for unexpected TMM process terminations, which may indicate exploitation attempts.

Detection coverage 2

Detect Anomalous UDP Traffic Targeting F5 Devices

low

Detects anomalous UDP traffic patterns potentially related to CVE-2026-41956 exploitation attempts by monitoring for unusual packet sizes or frequencies targeting F5 devices.

sigma tactics: denial_of_service techniques: T1499.004 sources: network_connection, windows

Detect TMM Process Termination

medium

Detects unexpected terminations of the Traffic Management Microkernel (TMM) process, potentially indicating exploitation of CVE-2026-41956.

sigma tactics: denial_of_service techniques: T1499.004 sources: process_creation, linux

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