CVE-2026-26078: Discourse is an open source discussion platform. Prior to versions 2025.12.2, 2026.1.1, and 2026.2.0, when the `patreon_webhook_secret` site setting i...

Description

Discourse is an open source discussion platform. Prior to versions 2025.12.2, 2026.1.1, and 2026.2.0, when the `patreon_webhook_secret` site setting is blank, an attacker can forge valid webhook signatures by computing an HMAC-MD5 with an empty string as the key. Since the request body is known to the sender, the attacker can produce a matching signature and send arbitrary webhook payloads. This allows unauthorized creation, modification, or deletion of Patreon pledge data and triggering patron-to-group synchronization. This vulnerability is patched in versions 2025.12.2, 2026.1.1, and 2026.2.0. The fix rejects webhook requests when the webhook secret is not configured, preventing signature forgery with an empty key. As a workaround, configure the `patreon_webhook_secret` site setting with a strong, non-empty secret value. When the secret is non-empty, an attacker cannot forge valid signatures without knowing the secret.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS Probability

0.22%

12.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-639

Affected Software

Vendor	Product	Versions
Discourse	Discourse	< 2025.12.0
Discourse	Discourse	>= 2026.1.0, < 2026.1.1
Discourse	Discourse	2026.2.0

References

https://github.com/discourse/discourse/security/advisories/GHSA-frx4-wg35-4r68Vendor Advisory

Timeline

Published: Feb 26, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-26078?

Discourse is an open source discussion platform. Prior to versions 2025.12.2, 2026.1.1, and 2026.2.0, when the `patreon_webhook_secret` site setting is blank, an attacker can forge valid webhook signatures by computing an HMAC-MD5 with an empty string as the key. Since the request body is known to the sender, the attacker can produce a matching signature and send arbitrary webhook payloads. This allows unauthorized creation, modification, or deletion of Patreon pledge data and triggering patron-to-group synchronization. This vulnerability is patched in versions 2025.12.2, 2026.1.1, and 2026.2.0. The fix rejects webhook requests when the webhook secret is not configured, preventing signature forgery with an empty key. As a workaround, configure the `patreon_webhook_secret` site setting with a strong, non-empty secret value. When the secret is non-empty, an attacker cannot forge valid signatures without knowing the secret.

How severe is CVE-2026-26078?

CVE-2026-26078 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.22% probability of exploitation in the next 30 days.

How do I fix CVE-2026-26078?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.