CVE-2026-107843
Received
Received - Intake
Email Flooding in Contao CMS via Unauthenticated Opt-In Token
Vulnerability report for CVE-2026-107843, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.
Publication date: 2026-10-09
Last updated on: 2026-10-09
Assigner: GitHub, Inc.
Description
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.
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| contao | contao | >= 4.1.0, < 5.3.50 |
| contao | contao | >= 5.4.0-RC1, < 5.7.12 |
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-770 | The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. |
| CWE-204 | The product provides different responses to incoming requests in a way that reveals internal state information to an unauthorized actor outside of the intended control sphere. |
