# CVE-2026-78156: Open5GS heap-based buffer overflow in S6a handler

Source: https://junglewise.ai/threats/cve-2026-78156-open5gs-heap-based-buffer-overflow-in-s6a-handler  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-24. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-78156 · Severity: high · CVSS 7.4 · Published 2026-08-24

Open5GS is an open-source 5G core network implementation used by telecom operators and testing environments. A heap-based buffer overflow in the S6a authentication handler allows an attacker to send a specially crafted network message with a malformed Visited-PLMN-Id field, potentially causing service crashes or remote code execution in the home subscriber server (HSS).

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

## Quick answers

**Is CVE-2026-78156 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-78156 being exploited in the wild.

**How severe is CVE-2026-78156?** High severity, with a CVSS score of 7.4, published 24 August 2026.

**Which products and versions are affected?** Open5GS 2.8.0.

**Is there a fix for CVE-2026-78156?** A patch was published on 2026-08-24: Patch commit a9c82ee0b590d76a581b0580cb46b598984e2392 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-78156 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-78156?** 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

A heap-based buffer overflow exists in the hss_ogs_diam_s6a_air_cb function in src/hss/hss-s6a-path.c, which processes Diameter Authentication-Information-Request (AIR) messages on the S6a interface. The vulnerability occurs because the function does not properly validate the length of the Visited-PLMN-Id AVP (Attribute-Value Pair) before using it in a memory operation, allowing an attacker to write beyond allocated buffer bounds. An attacker with network access to the S6a interface can remotely trigger this overflow by sending a malicious AIR message. The impact includes denial of service and potential code execution with HSS privileges. A patch (commit a9c82ee0b590d76a581b0580cb46b598984e2392) that adds length validation for the Visited-PLMN-Id field has been released.

## Affected products

- Open5GS Open5GS 2.8.0

## Timeline

- 2026-08-24: disclosed
- 2026-08-24: patched: Patch commit a9c82ee0b590d76a581b0580cb46b598984e2392

## References

- [https://github.com/open5gs/open5gs/](https://github.com/open5gs/open5gs/)
- [https://github.com/open5gs/open5gs/commit/a9c82ee0b590d76a581b0580cb46b598984e2392](https://github.com/open5gs/open5gs/commit/a9c82ee0b590d76a581b0580cb46b598984e2392)

## 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)