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CVE-2026-6739
medium
CVSS 6.7
Authorization Flaw in github.com/mattermost/mattermost-server (CVE-2026-6739)
Summary
vulnerability in github.com/mattermost/mattermost-server (CVE-2026-6739). Confidential information can be exposed externally. Mitigation: upgrade to `10.11.17` or later.
AI summary snake-internal / snake-material-v2
A vulnerability tracked as **CVE-2026-6739** has been found in github.com/mattermost/mattermost-server.
Confidential information can be exposed externally. CVSS score: 6.7/10.
What to do: upgrade github.com/mattermost/mattermost-server to **10.11.17** or later.
If unsure, ask your IT team or search "github.com/mattermost/mattermost-server CVE-2026-6739" on the vendor's site.
CVE-2026-6739 (github.com/mattermost/mattermost-server) — CWE-863 / CVSS v3 6.7
Attack vector: remote (network-reachable) / no user interaction
Patched: `10.11.17` — 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.
❓ What is the problem
**incorrect authorization** (CWE-863) exists in github.com/mattermost/mattermost-server.
📍 Affected scope
github.com/mattermost/mattermost-server — .
🔥 Severity
Severity: Medium (CVSS 6.7/10). Confidential information can be exposed externally
🔧 How to fix
Update to **10.11.17**.
🛡️ Workaround
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
🔍 Detection
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 (7 steps)
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。
-
6Apply patch patch
Upgrade github.com/mattermost/mattermost-server to 10.11.17ステージング環境で 10.11.17 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と、Step 3 で見つけた異常検知の続報チェックを含めること。
-
7Post-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 Step 3 と同じログクエリでアラート再発が無いか継続監視。
Affected packages
go
github.com/mattermost/mattermost-server
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"10.11.17"}]}]
go
github.com/mattermost/mattermost/server/v8
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"8.0.0-20260501142004-99b73d4c4acf"}]}]
References
- web https://nvd.nist.gov/vuln/detail/CVE-2026-6739
- web https://mattermost.com/security-updates
- web https://github.com/advisories/GHSA-m2w9-h2mm-79qr
- web https://github.com/mattermost/mattermost/pull/36197
- web https://github.com/mattermost/mattermost/pull/36377
- web https://github.com/mattermost/mattermost/pull/36379
- web https://github.com/mattermost/mattermost/pull/36380
- web https://github.com/mattermost/mattermost/pull/36382
- web https://github.com/mattermost/mattermost/commit/2c89c2f6768fbe4dfd57a21ca38c0aecead8d4a8
- web https://github.com/mattermost/mattermost/commit/5e159647b16e571b327ac6882f32eae42971f540
- web https://github.com/mattermost/mattermost/commit/8000e5933526f4fd66b92131db3a1b1f4520dbae
- web https://github.com/mattermost/mattermost/commit/f0a390b96e4c730daedbaf5190684776730218c7
- web https://github.com/mattermost/mattermost/releases/tag/v10.11.16
- web https://github.com/mattermost/mattermost/releases/tag/v11.5.5
- web https://github.com/mattermost/mattermost/releases/tag/v11.6.2
- web https://github.com/mattermost/mattermost/releases/tag/v11.7.0