CVE-2026-107843

Medium

Description

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.

SeverityMedium

CVSS5.3

Exploit probability—

ProductContao/core-bundle

PublishedOct 9, 2026

First seenOct 9, 2026

Weakness typeCWE-204CWE-204 CWE-770Allocation of resources without limits

How to fix

Update

contao/core-bundle5.3.50, 5.7.12 or later

Affected products

Product	Affected versions	Fixed in
contao/core-bundlePackagist	4.1.0 ≤ v < 5.3.50, 5.4.0-RC1 ≤ v < 5.7.12	5.3.50, 5.7.12

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