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TI-2026-21601 Aliases CVE-2026-27151

Discourse doesn't validate destination topic when moving posts

Priority LOW 7CWE-862Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
Security bypass
Confidentiality · integrity · availability
None · Low · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-862.

Summary

Discourse is an open source discussion platform. Prior to versions 2025.12.2, 2026.1.1, and 2026.2.0, the `move_posts` action only checked `can_move_posts?` on the source topic but never validated write permissions on the destination topic. This allowed TL4 users and category group moderators to move posts into topics in categories where they lack posting privileges (e.g., read-only categories or categories with group-restricted write access). Versions 2025.12.2, 2026.1.1, and 2026.2.0 patch the issue. No known workarounds are available.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00179 7th percentileScored 2026-11-07
Fix Fixed discourse (discourse): 2025.12.2, 2026.1.1, 2026.2.0

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 2025.12.2; 2026.1.0-latest to before 2026.1.1; 2026.2.0-latest to before 2026.2.02025.12.2, 2026.1.1, 2026.2.0Patch availableCNA
  • discourse Vendordiscourse Affected before 2025.12.2; 2026.1.0-latest to before 2026.1.1; 2026.2.0-latest to before 2026.2.0 Fixed in 2025.12.2, 2026.1.1, 2026.2.0 Patch available CNA

CPE configurations NVD · 2

CPEVersionsRoleVendor
cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:*before 2025.12.2; 2026.1.0 to before 2026.1.1Vulnerablediscourse
cpe:2.3:a:discourse:discourse:2026.2.0:*:*:*:latest:*:*:*2026.2.0Vulnerablediscourse
  • cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:* Versions before 2025.12.2; 2026.1.0 to before 2026.1.1 Vulnerable ·discourse
  • cpe:2.3:a:discourse:discourse:2026.2.0:*:*:*:latest:*:*:* Versions 2026.2.0 Vulnerable ·discourse

Remediation

  • Fix · CNA discourse (discourse) Fixed in 2025.12.2, 2026.1.1, 2026.2.0

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-27151

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