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MEDIUM severity

Mattermost fails to properly validate login method restrictionsGHSA-3c9r-7f29-qp32

MEDIUMFix: mattermost/mattermost@61651b0

GHSA-3c9r-7f29-qp32 is a medium-severity (CVSS 5.4) CWE-303 vulnerability in github.com/mattermost/mattermost/server/v8. A fix is available for github.com/mattermost/mattermost/server/v8 — see the affected versions and patch details below.

Also known asCVE-2026-0999GO-2026-4520
Published
Updated
Affected
5 pkgs
Patched
2 / 5
Exploits
None indexed
Exploitation data as of Nov 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-3c9r-7f29-qp32.

EPSS Exploitation Probability

via FIRST.org ↗
0.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs10th percentile — riskier than 10% of all scored CVEsHighest risk
0.00%0.23%0.47%0.70%0.1%0.2%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

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

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 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to properly validate login method restrictions which allows an authenticated user to bypass SSO-only login requirements via userID-based authentication. Mattermost Advisory ID: MMSA-2025-00548

Affected Packages

5 total 2 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/mattermost/mattermost/server/v8all versions8.0.0-20251212052346-61651b0df7eago get github.com/mattermost/mattermost/server/v8@v8.0.0-20251212052346-61651b0df7ea
🐹Gogithub.com/mattermost/mattermost-server≥ 11.1.0No fix
🐹Gogithub.com/mattermost/mattermost-server≥ 10.11.0No fix
🐹Gogithub.com/mattermost/mattermost-server≥ 11.2.0No fix
🐹Gogithub.com/mattermost/mattermost-serverall versions5.3.2-0.20251212052346-61651b0df7eago get github.com/mattermost/mattermost-server@v5.3.2-0.20251212052346-61651b0df7ea

Affected Products

1 product · 3 configurations
Application
mattermost servermattermost
≥ 11.2.0 && < 11.2.2
range

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/v8, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update github.com/mattermost/mattermost/server/v8 to 8.0.0-20251212052346-61651b0df7ea or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3c9r-7f29-qp32 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.

Frequently Asked Questions

Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to properly validate login method restrictions which allows an authenticated user to bypass SSO-only login requirements via userID-based authentication. Mattermost Advisory ID: MMSA-2025-00548
O3 Security · Impact-Aware SCA

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Mattermost fails to properly validate login method…