Vulnerability in contao/core-bundle (CVE-2026-107850)
Summary
Vulnerability in contao/core-bundle (CVE-2026-107850). Risk of unauthorized operations or information disclosure. Exploitable via PreviewVoter. Mitigation: upgrade to 5.7.12 or later.
Original description
The description as published by the source.
core-bundle/config/services.yaml registers the preview access voter with the class Contao\CoreBundle\Security\Voter\DataContainer\PreviewAccessVoter, but the class shipped on disk is named PreviewVoter. Symfony resolves the class with getReflectionClass($class, false), gets null, silently skips the interface based autoconfiguration that would have tagged it as a voter, and the now untagged private service is removed when the container is compiled. The application boots without a warning, and the ownership rule in PreviewVoter::hasAccess() is never executed. tl_preview_link has no compensating SQL filter on createdBy, so any non administrator back end user whose group holds the preview_link module reads every preview link on the installation and lifts the already signed share URLs straight out of the list. Following one grants front end preview of the target page, with showUnpublished and with no page permission check, to anyone at all.
Impact
A non administrator back end user reads every preview link on the installation, including links created by administrators, and lifts the already signed share URLs out of the list. Following one grants front end preview of the target page with showUnpublished and with no page permission check at all, so unpublished or embargoed content becomes readable by a user who has no rights on those pages, and by anyone that user forwards the URL to.
Honesty caveat, stated because it bounds the severity. `UpdateActio…
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-2026-107850 has been found in contao/core-bundle.
Attackers can target a specific entry point like PreviewVoter over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 4.3/10.
What to do: upgrade contao/core-bundle to 5.7.12 or later.
If unsure, ask your IT team or search "contao/core-bundle CVE-2026-107850" on the vendor's site.
CVE-2026-107850 (contao/core-bundle) — CWE-639 / CVSS v3 4.3
Attack vector: remote (network-reachable) / no user interaction
Attack surface: PreviewVoter / null / tl_preview_link / createdBy
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.
A vulnerability (CWE-639) exists in contao/core-bundle. Attackers reach the vulnerable code path via PreviewVoter.
Check the vendor advisory for the affected versions of contao/core-bundle. Attack surface: PreviewVoter / null / tl_preview_link / createdBy.
Severity: Medium (CVSS 4.3/10). Risk of unauthorized operations or information disclosure.
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/core-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/core-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/core-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/core-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。