Vulnerability in contao/core-bundle (CVE-2026-107843)
Summary
Vulnerability in contao/core-bundle (CVE-2026-107843). Risk of unauthorized operations or information disclosure. Exploitable via FORM_SUBMIT. Mitigation: upgrade to 5.7.12 or later.
Original description
The description as published by the source.
ModuleRegistration::compile() reaches its follow-up registration branch on any POST to a page carrying the module. That branch checks neither FORM_SUBMIT nor the captcha result computed immediately above it, and resendActivationMail() leads to OptInToken::send(), which has no rate limit at all.
Impact
Anyone on the internet can make a Contao installation send unlimited mail to an address of their choosing, from the site's own sender and reputation, at one outbound message per HTTP request. That is both a nuisance for the recipient and a deliverability risk for the site operator. The same request is a reliable account oracle for "this address has a pending registration on this site", which is exactly the sort of membership fact a public site is usually expected not to disclose.
Honest bound. The target must have an unconfirmed registration, that is tl_member.disable = 1 together with an unconfirmed reg- opt-in token. An attacker can create that state for an arbitrary address, since registration requires no ownership proof, but on a site where reg_activate is off the branch is unreachable.
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-2026-107843 has been found in contao/core-bundle.
Attackers can target a specific entry point like FORM_SUBMIT over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
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-2026-107843" on the vendor's site.
CVE-2026-107843 (contao/core-bundle) — CWE-204 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: FORM_SUBMIT / reg_activate
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-204) exists in contao/core-bundle. Attackers reach the vulnerable code path via FORM_SUBMIT without authentication.
Check the vendor advisory for the affected versions of contao/core-bundle. Attack surface: FORM_SUBMIT / reg_activate.
Severity: Medium (CVSS 5.3/10). 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。
-
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
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com