🛡️ CVE-2025-66488 — discourse

🟡 CVSS 5.0 — Medium ✅ No Known Exploit CWE-116 OSV
5.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

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

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.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs low-level privileges on the target. A user must be tricked into taking some action. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity low, availability low.

Weakness class

CVE-2025-66488 is classified as CWE-116: Improper Encoding or Escaping of Output. Output is emitted without encoding it for the context it lands in, so data is interpreted as markup or code.

Affected software

CVE-2025-66488 is recorded against 1 package.

  • discourse

Timeline and source

Published on 2 February 2026 and last revised on 17 June 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

github.com (Web)
nvd.nist.gov (Web)

Details

Severity MEDIUM
CVSS Score 5.0
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:L
CWE CWE-116
Public Exploit ✅ No
Source OSV
Published 2026-02-02
Updated 2026-08-12
Modified 2026-06-17
Fix URL N/A

Affected Packages

Software From version Fixed in
discourse — —

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