{"id":"CVE-2026-107843","aliases":["GHSA-mfxh-vp55-7gc6"],"url":"https://o3.security/vulnerability/CVE-2026-107843","summary":"Contao: The registration module re-sends activation mails on any unauthenticated POST, with no throttle and no captcha check","details":"`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.\n\n### Impact\n\nAnyone 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.\n\n**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.","published":"2026-10-09T19:21:32.011Z","modified":"2026-10-24T02:30:21.959067172Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Packagist","name":"contao/core-bundle","fixedVersion":"5.3.50"},{"ecosystem":"Packagist","name":"contao/core-bundle","fixedVersion":"5.7.12"}],"fix":{"url":"https://github.com/contao/contao/commit/2ea6117f9049db7221679251cfc41e67d941a74b","label":"contao/contao@2ea6117"},"references":[{"type":"WEB","url":"https://github.com/contao/contao/releases/tag/5.3.50"},{"type":"WEB","url":"https://github.com/contao/contao/releases/tag/5.7.12"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/107xxx/CVE-2026-107843.json"},{"type":"ADVISORY","url":"https://github.com/contao/contao/security/advisories/GHSA-mfxh-vp55-7gc6"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-107843"},{"type":"FIX","url":"https://github.com/contao/contao/commit/2ea6117f9049db7221679251cfc41e67d941a74b"},{"type":"PACKAGE","url":"https://github.com/contao/contao"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-24T02:30:21.959067172Z"}}