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CVE-2026-28741
Cross-Site Request Forgery (CSRF) in github.com/mattermost/mattermost-server (CVE-2026-28741)
Summary
vulnerability in github.com/mattermost/mattermost-server (CVE-2026-28741). Confidential information can be exposed externally. Mitigation: upgrade to `11.3.3+incompatible, 11.4.3+incompatible, 11.5.0+incompatible` or later.
AI summary snake-internal / snake-material-v2
A vulnerability tracked as **CVE-2026-28741** has been found in github.com/mattermost/mattermost-server.
Confidential information can be exposed externally. CVSS score: ?/10.
What to do: upgrade github.com/mattermost/mattermost-server to **11.3.3+incompatible, 11.4.3+incompatible, 11.5.0+incompatible** or later.
If unsure, ask your IT team or search "github.com/mattermost/mattermost-server CVE-2026-28741" on the vendor's site.
CVE-2026-28741 (github.com/mattermost/mattermost-server) — CWE-352 /
Attack vector: remote (network-reachable) / unauthenticated
Patched: `11.3.3+incompatible, 11.4.3+incompatible, 11.5.0+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
**CSRF** (CWE-352) exists in github.com/mattermost/mattermost-server.
📍 Affected scope
github.com/mattermost/mattermost-server — .
🔥 Severity
Severity: ?. Confidential information can be exposed externally
🔧 How to fix
Update to **11.3.3+incompatible, 11.4.3+incompatible, 11.5.0+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 11.3.3+incompatible, 11.4.3+incompatible, 11.5.0+incompatibleステージング環境で 11.3.3+incompatible, 11.4.3+incompatible, 11.5.0+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":"11.3.0-rc1+incompatible"},{"fixed":"11.3.3+incompatible"},{"introduced":"11.4.0-rc1+incompatible"},{"fixed":"11.4.3+incompatible"},{"introduced":"11.5.0-rc1+incompatible"},{"fixed":"11.5.0+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":"11.3.0-rc1"},{"fixed":"11.3.3"}]}]