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TI-2025-40912 Aliases CVE-2025-66488

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

Priority LOW 27CWE-116Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Required
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
Low · Low · None
Fix status
Fixed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00198 9th percentileScored 2026-11-07
Fix Fixed discourse (discourse): 3.5.4, 2025.11.2, 2025.12.1 +1

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
discoursediscoursebefore 3.5.4; 2025.11.0-latest to before 2025.11.2; 2025.12.0-latest to before 2025.12.1; 2026.1.0-latest to before 2026.1.03.5.4, 2025.11.2, 2025.12.1, 2026.1.0Patch availableCNA
  • discourse Vendordiscourse Affected before 3.5.4; 2025.11.0-latest to before 2025.11.2; 2025.12.0-latest to before 2025.12.1; 2026.1.0-latest to before 2026.1.0 Fixed in 3.5.4, 2025.11.2, 2025.12.1, 2026.1.0 Patch available CNA

CPE configurations NVD · 3

CPEVersionsRoleVendor
cpe:2.3:a:discourse:discourse:*:*:*:*:stable:*:*:*before 3.5.4; 2025.11.0 to before 2025.11.2Vulnerablediscourse
cpe:2.3:a:discourse:discourse:2025.12.0:*:*:*:stable:*:*:*2025.12.0Vulnerablediscourse
cpe:2.3:a:discourse:discourse:2026.1.0:*:*:*:stable:*:*:*2026.1.0Vulnerablediscourse
  • cpe:2.3:a:discourse:discourse:*:*:*:*:stable:*:*:* Versions before 3.5.4; 2025.11.0 to before 2025.11.2 Vulnerable ·discourse
  • cpe:2.3:a:discourse:discourse:2025.12.0:*:*:*:stable:*:*:* Versions 2025.12.0 Vulnerable ·discourse
  • cpe:2.3:a:discourse:discourse:2026.1.0:*:*:*:stable:*:*:* Versions 2026.1.0 Vulnerable ·discourse

Remediation

  • Fix · CNA discourse (discourse) Fixed in 3.5.4, 2025.11.2, 2025.12.1, 2026.1.0

Timeline

  1. 2026-10-02 Threatist record created from CVE-2025-66488

References

Advisory 1

  • TI-2021-19656 Denial of Service in discourse CVSS 3.1MEDIUM 6.8
  • TI-2024-36150 Potential Backup file leaked via Nginx in Discourse CVSS 3.1HIGH 7.5
  • TI-2021-18002 RCE via malicious SNS subscription payload CVSS 3.1CRITICAL 10.0
  • TI-2026-24651 Discourse: Open redirect via `sso_destination_url` cookie in `enter` CVSS 4.0MEDIUM 5.1
  • TI-2026-22278 Discourse leaks private topic title and post excerpt via user action API endpoint CVSS 4.0HIGH 8.7
  • TI-2023-24152 Unauthenticated access to new private chat messages in Discourse CVSS 3.1HIGH 7.5
See all 262 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences