CVE-2025-66488CWE-116

Discourse allows script execution in uploaded HTML/XML files on S3

Medium · published January 28, 2026

CVSS v3.1
4.6
EPSS
0%
Percentile
9.5
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
4.6 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:L
CVSS v4.0
Not supplied
EPSS
0.00201 · 9.5th percentile
Weakness
CWE-116 · Improper Encoding or Escaping of Output
Published
2026-01-28T18:15Z
EPSS history
Timeline
  • 28 JAN 18:15Z
    Discourse allows script execution in uploaded HTML/XML files on S3
    cvelistv5