What’s Vulnerable › Vulnerabilities

CVE-2026-107843: Contao: The registration module re-sends activation mails on any unauthenticated POST, with no throttle and no captcha check

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-09 · updated 2026-10-16
• Weakness: CWE-204

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.

Affected products

• contao: from 4.1.0, < 5.3.50; from 5.4.0-RC1, < 5.7.12

References

• https://github.com/contao/contao/commit/2ea6117f9049db7221679251cfc41e67d941a74b
• https://github.com/contao/contao/releases/tag/5.3.50
• https://github.com/contao/contao/releases/tag/5.7.12
• https://github.com/contao/contao/security/advisories/GHSA-mfxh-vp55-7gc6

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