Vulnerability in github.com/mattermost/mattermost-server (CVE-2026-3473)
Summary
Vulnerability in github.com/mattermost/mattermost-server (CVE-2026-3473). Confidential information can be exposed externally. Mitigation: upgrade to 10.11.15 or later.
Original description
The description as published by the source.
Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate file ownership and access control, which allows an authenticated user to access and download files belonging to other users or teams via crafted Boards API requests using valid file IDs. Mattermost Advisory ID: MMSA-2026-00620.
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-2026-3473 has been found in github.com/mattermost/mattermost-server.
Confidential information can be exposed externally. CVSS score: 5.9/10.
What to do: upgrade github.com/mattermost/mattermost-server to 10.11.15 or later.
If unsure, ask your IT team or search "github.com/mattermost/mattermost-server CVE-2026-3473" on the vendor's site.
CVE-2026-3473 (github.com/mattermost/mattermost-server) — CWE-639 / CVSS v3 5.9
Attack vector: remote (network-reachable) / no user interaction
Patched: 10.11.15 — 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.
A vulnerability (CWE-639) exists in github.com/mattermost/mattermost-server.
Check the vendor advisory for the affected versions of github.com/mattermost/mattermost-server.
Severity: Medium (CVSS 5.9/10). Confidential information can be exposed externally.
Update to 10.11.15.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
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
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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。 -
2Apply patch patch
Upgrade github.com/mattermost/mattermost-server to 10.11.15ステージング環境で 10.11.15 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。
-
3Post-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
References
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- web mattermost.com