Cross-Site Scripting (XSS) in contao/comments-bundle (CVE-2026-107845)
Summary
Cross-site scripting in contao/comments-bundle (CVE-2026-107845). Confidential information can be exposed externally. Mitigation: upgrade to 5.7.12 or later.
Original description
The description as published by the source.
An unauthenticated front end visitor can post a comment containing a XSS injection. The victim is any back end user who opens the Comments module, and moderation makes exposure certain rather than preventing it. No Content-Security-Policy header is sent on the Contao back end, so nothing mitigates the inline handler.
Impact
Anyone on the internet can inject script that executes in the Contao back end origin, under the session of whichever user opens the Comments module, with no click and no hover. From there the payload acts as that user through the back end: reading any module they can reach, creating a new administrator, or editing a template, which on Contao is a documented path from back end write access to code execution. Moderation does not help and in fact guarantees exposure, since unpublished comments are still inserted and a moderator has to open the list to act on them.
Source: NIST National Vulnerability Database 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-2026-107845 has been found in contao/comments-bundle.
Confidential information can be exposed externally. CVSS score: 9.3/10.
What to do: upgrade contao/comments-bundle to 5.7.12 or later.
If unsure, ask your IT team or search "contao/comments-bundle CVE-2026-107845" on the vendor's site.
CVE-2026-107845 (contao/comments-bundle) — CWE-79 / CVSS v3 9.3
Attack vector: remote (network-reachable) / unauthenticated
Patched: 5.7.12 — 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.
Cross-site scripting (XSS) (CWE-79) exists in contao/comments-bundle.
Check the vendor advisory for the affected versions of contao/comments-bundle.
Severity: Critical (CVSS 9.3/10). Confidential information can be exposed externally.
Update to 5.7.12.
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 'contao/comments-bundle' . 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 'contao/comments-bundle' . | 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
contao/comments-bundle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 contao/comments-bundle to 5.7.12ステージング環境で 5.7.12 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。
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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。