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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.

Original description

The description as published by the source.

Mattermost doesn't require system-level permission when patching protected default system roles in github.com/mattermost/mattermost-server

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-2026-6739 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

Check the vendor advisory for the affected versions of 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

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify 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。

  2. 2
    Apply 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を含めること。

  3. 3
    Post-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

go github.com/mattermost/mattermost-server
[{"type":"SEMVER","events":[{"introduced":"10.11.0+incompatible"},{"fixed":"10.11.17+incompatible"},{"introduced":"11.5.0+incompatible"},{"fixed":"11.5.5+incompatible"},{"introduced":"11.6.0+incompatible"},{"fixed":"11.6.1+incompatible"}]}]
go github.com/mattermost/mattermost/server/v8
[{"type":"SEMVER","events":[{"introduced":"8.0.0-20250731163400-5b955468ea1e"},{"fixed":"8.0.0-20260501142004-99b73d4c4acf"}]}]
Go github.com/mattermost/mattermost-server/v5
[{"type":"SEMVER","events":[{"introduced":"0"}]}]
Go github.com/mattermost/mattermost-server/v6
[{"type":"SEMVER","events":[{"introduced":"0"}]}]

References

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