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GHSA-r5vf-grcx-5vqp

MEDIUM

Mattermost allows authenticated users to gain access to private repositories

Also known asCVE-2026-28735GO-2026-5839
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-plugin-github

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 validate the OAuth token scope on the callback which allows an authenticated Mattermost user to gain access to private repositories via modifying the scope parameter in the GitHub authorization URL. Mattermost Advisory ID: MMSA-2026-00628

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-plugin-githuball versions1.0.1-0.20260318132218-6e6b740c4852

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-r5vf-grcx-5vqp 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-r5vf-grcx-5vqp 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-r5vf-grcx-5vqp. 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 validate the OAuth token scope on the callback which allows an authenticated Mattermost user to gain access to private repositories via modifying the scope parameter in the GitHub authorization URL. Mattermost Advisory ID: MMSA-2026-00628
O3 Security · Impact-Aware SCA

Is GHSA-r5vf-grcx-5vqp in your dependencies?

O3 detects GHSA-r5vf-grcx-5vqp across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.