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CVE-2026-4274
Authorization Flaw in github.com/mattermost/mattermost-server (CVE-2026-4274)
Summary
vulnerability in github.com/mattermost/mattermost-server (CVE-2026-4274). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to `10.11.11+incompatible, 11.2.3+incompatible, 11.3.2+incompatible, 11.4.1+incompatible` or later.
AI summary snake-internal / snake-material-v2
A vulnerability tracked as **CVE-2026-4274** has been found in github.com/mattermost/mattermost-server.
Risk of unauthorized operations or information disclosure. CVSS score: ?/10.
What to do: upgrade github.com/mattermost/mattermost-server to **10.11.11+incompatible, 11.2.3+incompatible, 11.3.2+incompatible, 11.4.1+incompatible** or later.
If unsure, ask your IT team or search "github.com/mattermost/mattermost-server CVE-2026-4274" on the vendor's site.
CVE-2026-4274 (github.com/mattermost/mattermost-server) — CWE-863 /
Attack vector: remote (network-reachable) / no user interaction
Patched: `10.11.11+incompatible, 11.2.3+incompatible, 11.3.2+incompatible, 11.4.1+incompatible` — 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: ?. Risk of unauthorized operations or information disclosure
🔧 How to fix
Update to **10.11.11+incompatible, 11.2.3+incompatible, 11.3.2+incompatible, 11.4.1+incompatible**.
🛡️ 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
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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。
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6Apply patch patch
Upgrade github.com/mattermost/mattermost-server to 10.11.11+incompatible, 11.2.3+incompatible, 11.3.2+incompatible, 11.4.1+incompatibleステージング環境で 10.11.11+incompatible, 11.2.3+incompatible, 11.3.2+incompatible, 11.4.1+incompatible 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。
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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":"SEMVER","events":[{"introduced":"10.11.0-rc1+incompatible"},{"fixed":"10.11.11+incompatible"},{"introduced":"11.2.0-rc1+incompatible"},{"fixed":"11.2.3+incompatible"},{"introduced":"11.3.0-rc1+incompatible"},{"fixed":"11.3.2+incompatible"},{"introduced":"11.4.0-rc1+incompatible"},{"fixed":"11.4.1+incompatible"}]}]
Go
github.com/mattermost/mattermost-server/v5
[{"type":"SEMVER","events":[{"introduced":"0"}]}]
Go
github.com/mattermost/mattermost-server/v6
[{"type":"SEMVER","events":[{"introduced":"0"}]}]
Go
github.com/mattermost/mattermost/server/v8
[{"type":"SEMVER","events":[{"introduced":"8.0.0-20260105080200-d27a2195068d"},{"fixed":"8.0.0-20260217110922-b7d4a1f1f59b"}]}]