ZeroDay Findings
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Findings

CVE-2026-107843

Contao: The registration module re-sends activation mails

Published Oct 9, 2026 · updated Oct 9, 2026

reaches its follow-up registration branch on **any** POST to a page carrying the module. That branch checks neither nor the captcha result computed immediately above it, and leads to , 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 together with an unconfirmed opt-in token. An attacker can create that state for an arbitrary address, since registration requires no ownership proof, but on a site where is off the branch is unreachable.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 9, 2026 · Catalog

    Detected

    reaches its follow-up registration branch on **any** POST to a page carrying the module. That branch checks neither nor the captcha result computed immediately above it, and leads to , 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 messag

  2. Oct 9, 2026 · Catalog

    Fix available

    Packagist contao/core-bundle 4.1.0 → 5.3.50

  3. Oct 9, 2026 · Catalog

    Fix available

    Packagist contao/core-bundle 5.4.0-RC1 → 5.7.12

  4. Oct 9, 2026 · Catalog

    Updated

    reaches its follow-up registration branch on **any** POST to a page carrying the module. That branch checks neither nor the captcha result computed immediately above it, and leads to , 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 messag

Affected

  • Packagist contao/core-bundle4.1.0 → 5.3.50
  • Packagist contao/core-bundle5.4.0-RC1 → 5.7.12

Sources

References