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MEDIUM severity

CVE-2023-5967 — mattermost-server

MEDIUM

CVE-2023-5967 is a medium-severity (CVSS 4.3) CWE-754 vulnerability in github.com/mattermost/mattermost-server/v6. A fix is available for github.com/mattermost/mattermost-server/v6 — see the affected versions and patch details below.

Denial of Service via crashing the Calls Plugin

Also known asGHSA-xvq6-h898-wcj8
Published
Updated
Affected
4 pkgs
Patched
4 / 4
Exploits
None indexed
Exploitation data as of Nov 7, 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 CVE-2023-5967.

EPSS Exploitation Probability

via FIRST.org ↗
0.6%probability of exploitation in next 30 days
Lower Risk+0.10%
Lower risk than most CVEs50th percentile — riskier than 50% of all scored CVEsHighest risk
0.00%0.37%0.74%1.11%0.1%0.6%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

4 pkgs affected
🐹github.com/mattermost/mattermost-server/v6🐹github.com/mattermost/mattermost/server/v8🐹github.com/mattermost/mattermost/server/v8🐹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 fails to properly validate requests to the Calls plugin, allowing an attacker sending a request without a User Agent header to cause a panic and crash the Calls plugin

Affected Packages

4 total 4 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/mattermost/mattermost-server/v6all versions7.8.12go get github.com/mattermost/mattermost-server/v6@v7.8.12
🐹Gogithub.com/mattermost/mattermost/server/v8≥ 8.0.0&&< 8.0.48.0.4go get github.com/mattermost/mattermost/server/v8@v8.0.4
🐹Gogithub.com/mattermost/mattermost/server/v8≥ 8.1.0&&< 8.1.38.1.3go get github.com/mattermost/mattermost/server/v8@v8.1.3
🐹Gogithub.com/mattermost/mattermost/server/v8≥ 9.0.0&&< 9.0.19.0.1go get github.com/mattermost/mattermost/server/v8@v9.0.1

Affected Products

1 product · 3 configurations
Application
mattermostmattermost
≥ 8.1.0 && ≤ 8.1.2
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/v6, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update github.com/mattermost/mattermost-server/v6 to 7.8.12 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-5967 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 fails to properly validate requests to the Calls plugin, allowing an attacker sending a request without a User Agent header to cause a panic and crash the Calls plugin
O3 Security · Impact-Aware SCA

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CVE-2023-5967: mattermost-server — Fixed in 7.8.12