CVE-2025-66488

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

Published Jan 28, 2026 CVSS 3.1 · 4.6 Medium EPSS < 1% KEV · Not listed
Description
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

Sign in to view the affected projects.

Advisories

No advisories available
History
Type Values Removed Values Added
CPEs cpe:2.3:a:discourse:discourse:*:*:*:*:stable:*:*:*
cpe:2.3:a:discourse:discourse:2025.12.0:*:*:*:stable:*:*:*
cpe:2.3:a:discourse:discourse:2026.1.0:*:*:*:stable:*:*:*
Type Values Removed Values Added
First Time appeared Discourse
Discourse discourse
Vendors & Products Discourse
Discourse discourse
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Description 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.
Title Discourse allows script execution in uploaded HTML/XML files on S3
Weaknesses CWE-116
References
Metrics cvssV3_1

{'score': 4.6, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:L'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Jan 28, 2026, 7:29 PM
Reserved
Dec 2, 2025, 10:44 PM
Status
Analyzed
Published
Jan 28, 2026, 7:16 PM
Modified
Jun 17, 2026, 9:56 AM