Vulnerability in github.com/mattermost/mattermost-server (CVE-2026-5308)
Summary
Vulnerability in github.com/mattermost/mattermost-server (CVE-2026-5308). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 10.11.15 or later.
Original description
The description as published by the source.
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 enforce request body size limits on plugin HTTP endpoints which allows an attacker to cause a denial of service via crafted oversized HTTP requests.. Mattermost Advisory ID: MMSA-2026-00646
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-5308 has been found in github.com/mattermost/mattermost-server.
Risk of unauthorized operations or information disclosure. CVSS score: 4.9/10.
What to do: upgrade github.com/mattermost/mattermost-server to 10.11.15 or later.
If unsure, ask your IT team or search "github.com/mattermost/mattermost-server CVE-2026-5308" on the vendor's site.
CVE-2026-5308 (github.com/mattermost/mattermost-server) — CWE-400 / CVSS v3 4.9
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 10.11.15 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-400) exists in github.com/mattermost/mattermost-server.
Check the vendor advisory for the affected versions of github.com/mattermost/mattermost-server.
Severity: Medium (CVSS 4.9/10). Risk of unauthorized operations or information disclosure.
Update to 10.11.15.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'github.com/mattermost/mattermost-server' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'github.com/mattermost/mattermost-server' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
github.com/mattermost/mattermost-serverを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade github.com/mattermost/mattermost-server to 10.11.15ステージング環境で 10.11.15 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- web mattermost.com
- web github.com