Your RSA-2048 keys break in 2030. Find every one of them before attackers do.
🐹 Go

GHSA-5gmf-x7hg-97wf

MEDIUM

Mattermost doesn't filter nil elements from outgoing webhook attachment payloads before processing

Also known asCVE-2026-4915GO-2026-5845
Published
May 26, 2026
Updated
Jul 7, 2026
Affected
5 pkgs
Patched
5 / 5
Exploits
None indexed

Blast Radius

5 pkgs affected
🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost/server/v8

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to filter nil elements from outgoing webhook attachment payloads before processing, which allows an authenticated user to cause a denial of service (server process termination) via a crafted webhook callback response containing a null attachment entry. Mattermost Advisory ID: MMSA-2026-00641

Affected Packages

5 total 5 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/mattermost/mattermost-server11.6.0&&< 11.6.111.6.1
🐹Gogithub.com/mattermost/mattermost-server11.5.0&&< 11.5.411.5.4
🐹Gogithub.com/mattermost/mattermost-server11.4.0&&< 11.4.511.4.5
🐹Gogithub.com/mattermost/mattermost-server10.11.0&&< 10.11.1510.11.15
🐹Gogithub.com/mattermost/mattermost/server/v8all versions8.0.0-20260407102538-faa7d75b4ea0

Detection & mitigation playbook

Open-source dependency
  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/mattermost/mattermost-server. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

  2. Fix

    Update github.com/mattermost/mattermost-server to 11.6.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-5gmf-x7hg-97wf is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 pinpoints whether GHSA-5gmf-x7hg-97wf is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to GHSA-5gmf-x7hg-97wf. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to filter nil elements from outgoing webhook attachment payloads before processing, which allows an authenticated user to cause a denial of service (server process termination) via a crafted webhook callback response containing a null attachment entry. Mattermost Advisory ID: MMSA-2026-00641
O3 Security · Impact-Aware SCA

Is GHSA-5gmf-x7hg-97wf in your dependencies?

O3 detects GHSA-5gmf-x7hg-97wf across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.