Medium severity · published Jan 28, 2026
CVE-2025-66488
Discourse allows script execution in uploaded HTML/XML files on S3
6.1
CVSS
0.2%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 10% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
DI
discourse · discourse
< 3.5.4; >= 2025.11.0-latest, < 2025.11.2; >= 2025.12.0-latest, < 2025.12.1; >= 2026.1.0-latest, < 2026.1.0 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-66488
CVE.org
https://www.cve.org/CVERecord?id=CVE-2025-66488
Third Party Advisory
https://github.com/discourse/discourse/security/advisories/GHSA-68jp-3934-62rx
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