Resource exhaustion in Contao
CVE-2026-107843
Contao is an Open Source CMS. From version 4.1.0 until 5.3.50 and 5.7.12, ModuleRegistration::compile() enters its follow-up registration branch on any POST to a page containing the registration module without verifying FORM_SUBMIT or the preceding captcha result. resendActivationMail() can then invoke OptInToken::send() without rate limiting, allowing an unauthenticated attacker to cause repeated activation emails to be sent to an address with a pending registration and to determine whether that pending registration exists. The branch is reachable only when reg_activate is enabled and the target has an unconfirmed registration and opt-in token. This issue is fixed in versions 5.3.50 and 5.7.12.
Published .
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
- Contao — versions >= 4.1.0, < 5.3.50, >= 5.4.0-RC1, < 5.7.12
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-107843?
- CVE-2026-107843 is a medium-severity vulnerability in Contao, classified under Observable Response Discrepancy. CVSS score: 5.3/10. Published 2026-10-09.
- How severe is CVE-2026-107843?
- Medium severity. CVSS v3 base score is 5.3 out of 10.