Executive Summary

CVE-2026-8226 is a security flaw in Open5GS up to version 2.7.7 that causes a denial of service by crashing the Policy Control Function (PCF). The vulnerability occurs when the PCF processes malformed flow descriptions, specifically when a flow description contains the value "permit in" without the expected "from" substring. This mismatch between the parser and business logic triggers an assertion failure in the function handling flow descriptions, leading to a crash and restart of the PCF process.

The crash happens during both creation and update operations of application sessions via POST and PATCH requests to the PCF API endpoint. Instead of rejecting malformed inputs with a client error, the PCF crashes, making the service unavailable.

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Impact Analysis

This vulnerability can impact you by causing a denial of service in the Open5GS Policy Control Function. An attacker can remotely send malformed flow descriptions that crash the PCF process, causing it to restart and temporarily become unavailable.

Such denial of service can disrupt network policy enforcement and affect the availability of services relying on Open5GS, potentially leading to degraded network performance or outages.

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Detection Guidance

This vulnerability can be detected by monitoring for crashes or restarts of the Open5GS PCF (Policy Control Function) process, especially when it processes malformed flow descriptions in app session create or update requests.

Specifically, the crash is triggered by malformed POST or PATCH requests to the endpoint /npcf-policyauthorization/v1/app-sessions containing a flow description field with the value ["permit in"] instead of the expected format starting with "permit in from".

To detect exploitation attempts, you can monitor your web server or PCF logs for such malformed requests.

• Use network traffic capture tools like tcpdump or Wireshark to filter HTTP POST or PATCH requests to /npcf-policyauthorization/v1/app-sessions.
• Example tcpdump command to capture relevant traffic: tcpdump -i <interface> -A 'tcp port 80 or 443 and (((tcp[((tcp[12:1] & 0xf0) >> 2):4]) = 0x504f5354) or ((tcp[((tcp[12:1] & 0xf0) >> 2):5]) = 0x50415443)) and (tcp[((tcp[12:1] & 0xf0) >> 2)+20:] contains "/npcf-policyauthorization/v1/app-sessions")'
• Check Open5GS PCF logs for assertion failures or process restarts related to flow description parsing errors.

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Mitigation Strategies

Immediate mitigation steps include monitoring and filtering malformed requests to the PCF endpoint to prevent the crash.

Since the vulnerability is triggered by malformed flow descriptions in POST and PATCH requests to /npcf-policyauthorization/v1/app-sessions, you can implement input validation or filtering at the network or application firewall level to block requests containing flow descriptions with the value ["permit in"] without the expected "from" clause.

Additionally, consider restarting the PCF process if it crashes and monitor for repeated crashes as an indicator of exploitation attempts.

Long term mitigation requires a patch or update from the Open5GS project, which has not yet responded to the issue.

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Compliance Impact

The provided information does not specify any direct impact of the CVE-2026-8226 vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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