Discourse up to 2025.12.1/2026.1.0 Webhook Endpoint WebhooksController improper authentication

Summaryinfo

A vulnerability was found in Discourse up to 2025.12.1/2026.1.0. It has been rated as critical. The affected element is the function WebhooksController of the component Webhook Endpoint. Performing a manipulation results in improper authentication. This vulnerability is identified as CVE-2026-26077. The attack can be initiated remotely. There is not any exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in Discourse up to 2025.12.1/2026.1.0. It has been classified as critical. This affects the function WebhooksController of the component Webhook Endpoint. The manipulation with an unknown input leads to a improper authentication vulnerability. CWE is classifying the issue as CWE-287. When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

Discourse is an open source discussion platform. Prior to versions 2025.12.2, 2026.1.1, and 2026.2.0, several webhook endpoints (SendGrid, Mailjet, Mandrill, Postmark, SparkPost) in the `WebhooksController` accepted requests without a valid authentication token when no token was configured. This allowed unauthenticated attackers to forge webhook payloads and artificially inflate user bounce scores, potentially causing legitimate user emails to be disabled. The Mailpace endpoint had no token validation at all. Starting in versions 2025.12.2, 2026.1.1, and 2026.2.0, all webhook endpoints reject requests with a 406 response when no authentication token is configured. As a workaround, ensure that webhook authentication tokens are configured for all email provider integrations in site settings (e.g., `sendgrid_verification_key`, `mailjet_webhook_token`, `postmark_webhook_token`, `sparkpost_webhook_token`). There's no current workaround for mailpace before getting this fix.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-26077 since 02/10/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 2025.12.2, 2026.1.1 or 2026.2.0 eliminates this vulnerability.

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Productinfo

Type

• Chat Software

Name

• Discourse

Version

• 2025.12.0
• 2025.12.1
• 2026.0
• 2026.1.0

License

• open-source

Website

• Product: https://github.com/discourse/discourse/

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