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CVE-2026-6961 high CVSS 7.6

Path Traversal in github.com/mattermost/mattermost-server (CVE-2026-6961)

Summary

Path traversal in github.com/mattermost/mattermost-server (CVE-2026-6961). Data can be tampered with by attackers. Mitigation: upgrade to 10.11.17 or later.

Original description

The description as published by the source.

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to sanitize FileInfo.Name received from federated peers during shared channel file sync, which allows an attacker who controls a federated server to write files to arbitrary locations within the target server's filestore via path traversal sequences in the filename field. Mattermost Advisory ID: MMSA-2026-00661

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-2026-6961 has been found in github.com/mattermost/mattermost-server.
Data can be tampered with by attackers. CVSS score: 7.6/10.
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-2026-6961" on the vendor's site.

CVE-2026-6961 (github.com/mattermost/mattermost-server) — CWE-22 / CVSS v3 7.6
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

Path traversal (CWE-22) 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: High (CVSS 7.6/10). Data can be tampered with by attackers.

🔧 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"},{"fixed":"10.11.17"}]}]
go github.com/mattermost/mattermost/server/v8
[{"type":"SEMVER","events":[{"introduced":"8.0.0-20250731163400-5b955468ea1e"},{"fixed":"8.0.0-20260423180926-c021eeaff8f0"}]}]
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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