# CVE-2026-91855: Open5GS PFCP Message Handler assertion failure in FAR validation

Source: https://junglewise.ai/threats/cve-2026-91855-open5gs-pfcp-message-handler-assertion-failure-in-far-validation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-15. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-91855 · Severity: medium · CVSS 5.3 · Published 2026-09-15

Open5GS is an open-source implementation of 5G core network infrastructure. A flaw in the PFCP (Packet Forwarding Control Protocol) message handler can cause the service to crash when processing maliciously crafted or malformed PFCP messages, disrupting 5G network operations and connectivity.

Technologies: [Open5GS](https://junglewise.ai/threats/technologies/open5gs). Vendors: [Open5GS](https://junglewise.ai/threats/vendors/open5gs).

## Quick answers

**Is CVE-2026-91855 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-91855 being exploited in the wild.

**How severe is CVE-2026-91855?** Medium severity, with a CVSS score of 5.3, published 15 September 2026.

**Which products and versions are affected?** Open5GS up to 2.7.7.

**Is there a fix for CVE-2026-91855?** A patch was published on 2026-08-06: Fix commit 028e1dbb5e3271035ccee906ef417a97fc523f71 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-91855 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-91855?** Check whether you run Open5GS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is an assertion failure (denial of service) in the PFCP Message Handler component (lib/pfcp/handler.c) affecting Open5GS up to version 2.7.7. The root cause is insufficient validation of the Outer Header Creation (OHC) IE (Information Element) in Create/Update FAR (Forwarding Action Rule) PFCP messages. Specifically, truncated or unsupported GTP-U/IPv6 IEs could be partially copied into a zero-initialized FAR structure, leaving incompletely initialized fields that later trigger an "Unknown family" assertion on subsequent requests. The attack is network-accessible and requires no authentication, as PFCP is a control-plane protocol exposed to the network. An attacker can craft malformed PFCP messages to crash the UPF (User Plane Function) or MME components. The fix (commit 028e1dbb5e3271035ccee906ef417a97fc523f71) validates OHC before copying and rejects invalid/unsupported variants.

## Affected products

- Open5GS Open5GS up to 2.7.7

## Timeline

- 2026-09-15: disclosed
- 2026-08-06: patched: Fix commit 028e1dbb5e3271035ccee906ef417a97fc523f71

## References

- [https://github.com/open5gs/open5gs/](https://github.com/open5gs/open5gs/)
- [https://github.com/open5gs/open5gs/commit/028e1dbb5e3271035ccee906ef417a97fc523f71](https://github.com/open5gs/open5gs/commit/028e1dbb5e3271035ccee906ef417a97fc523f71)

## Related threats

- [Open5GS HTTP/2 SBI server memory exhaustion](https://junglewise.ai/threats/cve-2026-106806-a-memory-exhaustion-issue-exists-in-open5gs-v2-8-0-in-the-http-2)
- [open5GS PFCP transaction handling denial of service](https://junglewise.ai/threats/cve-2026-106807-a-denial-of-service-vulnerability-exists-in-open5gs-v2-8-0-in)
- [Open5GS heap out-of-bounds write in multipart parsing](https://junglewise.ai/threats/cve-2026-116543-open5gs-1-3-0-through-2-8-0-contains-a-heap-out-of-bounds-write)
- [Open5GS assertion failure in SGSN context request handling](https://junglewise.ai/threats/cve-2026-108105-open5gs-through-2-8-0-contains-a-reachable-assertion)
- [Open5GS heap out-of-bounds read in PFCP parsing](https://junglewise.ai/threats/cve-2026-108103-open5gs-through-2-8-0-contains-a-heap-out-of-bounds-read)