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TI-2026-21604 Aliases CVE-2026-27154

Discourse has XSS when editing a malicious post

Priority LOW 13CWE-79Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
Cross-site scripting
Confidentiality · integrity · availability
None · None · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-79.

Summary

Discourse is an open source discussion platform. Prior to versions 2025.12.2, 2026.1.1, and 2026.2.0, a user full name can be evaluated as raw HTML when the following settings are set: `display_name_on_posts` => true; and `prioritize_username_in_ux` => false. Editing a post of a malicious user would trigger an XSS. 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 0.00178 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
Yes
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-2026-27154

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