Authorization Flaw in Mattermost (CVE-2026-19076)
Summary
Vulnerability in Mattermost (CVE-2026-19076). Data can be tampered with by attackers. Exploitable via POST /api/v4/users/login/switch...
Original description
The description as published by the source.
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to reject OAuth application sessions in the account type switch endpoint, which allows an attacker with a valid OAuth bearer token for a target user to permanently take over that user's SSO-backed account by setting an attacker-controlled password and detaching the account from its identity provider via a crafted request to POST /api/v4/users/login/switch.. Mattermost Advisory ID: MMSA-2026-00758
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-2026-19076 has been found in Mattermost.
Attackers can target a specific entry point like POST /api/v4/users/login/switch.. over the network to misuse the product.
Data can be tampered with by attackers. CVSS score: 4.4/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Mattermost CVE-2026-19076" on the vendor's site.
CVE-2026-19076 (Mattermost) — CWE-863 / CVSS v3 4.4
Attack vector: remote (network-reachable) / no user interaction
Attack surface: POST /api/v4/users/login/switch..
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.
Incorrect authorization (CWE-863) exists in Mattermost. Attackers reach the vulnerable code path via POST /api/v4/users/login/switch...
Check the vendor advisory for the affected versions of Mattermost. Attack surface: POST /api/v4/users/login/switch...
Severity: Medium (CVSS 4.4/10). Data can be tampered with by attackers.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual POST /api/v4/users/login/switch.. requests with malformed payloads or SQL meta-characters. Run grep -r 'Mattermost' . 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
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1Identify exposure identify
grep -r 'Mattermost' . | 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
Mattermostを grep し、稼働しているサービス・バージョンを把握する。 -
2Hunt for indicators of compromise detect
grep 'POST /api/v4/users/login/switch..' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'アクセスログで
POST /api/v4/users/login/switch..への異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。 -
3Post-deployment verification verify
Replay attack against POST /api/v4/users/login/switch.. on staging to confirm patch closes the vector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 2 と同じログクエリでアラート再発が無いか継続監視。