What is CVE-2025-66488?

CVE-2025-66488 is a medium-severity vulnerability in Discourse, classified under Improper Encoding or Escaping of Output. CVSS score: 4.6/10. Published 2026-01-28.

How severe is CVE-2025-66488?

Medium severity. CVSS v3 base score is 4.6 out of 10.

Vulnerability in Discourse

CVE-2025-66488

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.

EPSS: 0.002 (7.2th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.6 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:L.

Affected products

Discourse — versions >= 2026.1.0-latest, < 2026.1.0, >= 2025.12.0-latest, < 2025.12.1, < 3.5.4

Weakness classification (CWE)

CWE-116 — Improper Encoding or Escaping of Output

References

security-advisories@github.com (x_refsource_CONFIRM, Third Party Advisory)

Frequently asked questions

What is CVE-2025-66488?: CVE-2025-66488 is a medium-severity vulnerability in Discourse, classified under Improper Encoding or Escaping of Output. CVSS score: 4.6/10. Published 2026-01-28.
How severe is CVE-2025-66488?: Medium severity. CVSS v3 base score is 4.6 out of 10.