---
id: CVE-2026-107843
title: Contao is an Open Source CMS
summary: >-
  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 th…
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N'
cwe:
  - CWE-204
  - CWE-770
vendor: contao
product: contao/core-bundle
affected:
  - 'contao/core-bundle >= 4.1.0, < 5.3.50'
  - 'contao/core-bundle >= 5.4.0-RC1, < 5.7.12'
patched:
  - contao/core-bundle 5.3.50
  - contao/core-bundle 5.7.12
published: '2026-10-09'
updated: '2026-10-09'
sourceUpdated: '2026-10-09T20:17:10.167'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-107843'
references:
  - url: >-
      https://github.com/contao/contao/commit/2ea6117f9049db7221679251cfc41e67d941a74b
    label: security-advisories@github.com
  - url: 'https://github.com/contao/contao/releases/tag/5.3.50'
    label: security-advisories@github.com
  - url: 'https://github.com/contao/contao/releases/tag/5.7.12'
    label: security-advisories@github.com
  - url: 'https://github.com/contao/contao/security/advisories/GHSA-mfxh-vp55-7gc6'
    label: security-advisories@github.com
  - url: 'https://github.com/advisories/GHSA-mfxh-vp55-7gc6'
tags:
  - nvd
  - ghsa
  - composer
aliases:
  - GHSA-mfxh-vp55-7gc6
ecosystem: composer
ingestedAt: '2026-10-09T21:12:42.318Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-107843)

Affected packages:

- `contao/core-bundle >= 4.1.0, < 5.3.50`
- `contao/core-bundle >= 5.4.0-RC1, < 5.7.12`

Patched in:

- `contao/core-bundle 5.3.50`
- `contao/core-bundle 5.7.12`

Source: https://github.com/advisories/GHSA-mfxh-vp55-7gc6