CVE-2025-66488: Discourse

Medium severity, CVSS 6.1. EPSS: 0.2% chance of exploitation in the next 30 days.

Discourse is an open source discussion platform. A vulnerability present in versions prior to 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0 affects anyone who uses S3 for uploads. While scripts may be executed, they will only be run in the context of the S3/CDN domain, with no site credentials. Versions 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0 fix the issue. As a workaround, disallow html or xml files for uploads in authorized_extensions. For existing html xml uploads, site owners can consider deleting them.

Affected products

• Discourse Discourse: before 3.5.4 (fixed in 3.5.4); from 2025.11.0, before 2025.11.2 (fixed in 2025.11.2); version 2025.12.0 only; version 2026.1.0 only

Published 2026-01-28. Last modified 2026-06-17.