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CRITICAL severity

Mattermost Server allows attackers to gain privileges by accessing unintended API endpoints with users' credentialsGHSA-g78f-6xq7-rrhq

CRITICAL

GHSA-g78f-6xq7-rrhq is a critical-severity (CVSS 9.8) Improper Privilege Management vulnerability in github.com/mattermost/mattermost-server. A fix is available for github.com/mattermost/mattermost-server — see the affected versions and patch details below.

Also known asCVE-2017-18885GO-2025-4200
Published
Updated
Affected
3 pkgs
Patched
3 / 3
Exploits
None indexed
Exploitation data as of Nov 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs68th percentile — riskier than 68% of all scored CVEsHighest risk
0.00%0.56%1.12%1.68%0.4%1.2%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

3 pkgs affected
🐹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

An issue was discovered in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2. It allows attackers to gain privileges by accessing unintended API endpoints on a user's behalf.

Affected Packages

3 total 3 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/mattermost/mattermost-serverall versions4.1.2go get github.com/mattermost/mattermost-server@v4.1.2
🐹Gogithub.com/mattermost/mattermost-server≥ 4.2.0-rc1&&< 4.2.14.2.1go get github.com/mattermost/mattermost-server@v4.2.1
🐹Gogithub.com/mattermost/mattermost-server≥ 4.3.0-rc1&&< 4.3.04.3.0go get github.com/mattermost/mattermost-server@v4.3.0

Affected Products

1 product · 6 configurations
Application
mattermost servermattermost
≥ 4.2.0 && < 4.2.1
1 version
4.3.0

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

  2. Fix

    Update github.com/mattermost/mattermost-server to 4.1.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-g78f-6xq7-rrhq is resolved across your whole dependency graph.

  3. Workarounds

    Close the privilege gap rather than the entry point: audit which accounts, roles and service identities can reach the affected operation, drop the component to the least privilege it actually needs, and review file and directory permissions created by earlier installs — a default left in place is what makes this reachable.

Frequently Asked Questions

An issue was discovered in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2. It allows attackers to gain privileges by accessing unintended API endpoints on a user's behalf.
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Mattermost Server allows attackers to gain privileges by…