Impact Analysis

The vulnerability can be exploited remotely to cause a denial of service, potentially disrupting the normal operation of the affected Open5GS system.

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Executive Summary

This vulnerability exists in Open5GS up to version 2.7.7, specifically in the function smf_n4_build_qos_flow_to_modify_list within the SMF component. It allows an attacker to manipulate this function remotely, which leads to a denial of service condition.

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Compliance Impact

The provided information does not specify any direct impact of the CVE-2026-8250 vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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Detection Guidance

This vulnerability can be detected by monitoring for crashes or abnormal termination of the SMF process in Open5GS, especially exit code 139 which indicates a segmentation fault caused by processing an oversized flowInfos list.

Detection can also involve inspecting network traffic for suspicious POST requests to the endpoint /nsmf-callback/v1/sm-policy-notify/{smContextRef}/update containing an unusually large number of flowInfos elements (more than 15).

A practical approach is to check SMF logs for crash events and to capture and analyze HTTP POST requests to the specified endpoint.

• Use system commands like `journalctl -u open5gs-smfd` or `ps` and `dmesg` to detect SMF crashes or segmentation faults.
• Use network capture tools such as `tcpdump` or `wireshark` to filter and analyze POST requests to `/nsmf-callback/v1/sm-policy-notify/`.
• Example tcpdump command: `tcpdump -i <interface> -A 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'` and then filter HTTP POST requests to the vulnerable endpoint.

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Mitigation Strategies

Immediate mitigation involves preventing the SMF from processing oversized flowInfos lists that exceed the limit of 15 entries.

Since the vulnerability causes a denial of service by crashing the SMF process, you should monitor and restrict incoming POST requests to the vulnerable endpoint to ensure they do not contain more than 15 flowInfos elements.

If possible, apply input validation or filtering at the network or application level to reject requests with excessive flowInfos before they reach the SMF.

Additionally, consider temporarily disabling or restricting access to the /nsmf-callback/v1/sm-policy-notify/{smContextRef}/update endpoint until a patch or official fix is released.

Monitor SMF logs for crashes and restart the service as needed to maintain availability.

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