CVE-2026-26077
published 2026-02-26CVE-2026-26077: 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…
PriorityP351medium6.5CVSS 3.1
AVNACLPRNUINSUCNILAL
EXPLOIT
EPSS
1.14%
66.2th percentile
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.
Affected
6 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| discourse | discourse | < 2025.12.2 | 2025.12.2 |
| discourse | discourse | < 2025.12.0 | 2025.12.0 |
| discourse | discourse | — | — |
| discourse | discourse | — | — |
| discourse | discourse | — | — |
| discourse | discourse | >= 2026.1.0 < 2026.1.1 | 2026.1.1 |
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Nuclei
Discourse - Unauthenticated Mailpace Webhook Bounce-Score Forgery
nuclei·CVSS 6.5
CVE-2026-26077 [MEDIUM] Discourse - Unauthenticated Mailpace Webhook Bounce-Score Forgery
Discourse - Unauthenticated Mailpace Webhook Bounce-Score Forgery
Discourse's WebhooksController contains a missing-authentication flaw caused by accepting requests to provider webhook endpoints (including /webhooks/mailpace, SendGrid, Mailjet, Mandrill, Postmark, and SparkPost) without validating a token when none is configured, which is the default state, letting an unauthenticated attacker forge webhook payloads.
Template:
id: CVE-2026-26077
info:
name: Discourse - Unauthenticated Mailpace Webhook Bounce-Score Forgery
author: str4k3r
severity: medium
description: |
Discourse's WebhooksController contains a missing-authentication flaw caused by accepting requests to provider webhook endpoints (including /webhooks/mailpace, SendGrid, Mailjet, Mandrill, Postmark, and SparkPost) without
2026-02-26
Published