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TI-2021-16547 Aliases CVE-2021-39161

Cross-site scripting via category name in Discourse

Priority LOW 25CWE-79Published · Updated

Key facts

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

Attack profile from CVSS 3.1 · NVD. Fix status from CNA. Impact type from CWE-79.

Summary

Discourse is an open source platform for community discussion. In affected versions category names can be used for Cross-site scripting(XSS) attacks. This is mitigated by Discourse's default Content Security Policy and this vulnerability only affects sites which have modified or disabled or changed Discourse's default Content Security Policy have allowed for moderators to modify categories. This issue is patched in the latest stable, beta and tests-passed versions of Discourse. Users are advised to ensure that the Content Security Policy is enabled, and has not been modified in a way which would make it more vulnerable to XSS attacks.

Why it matters now

EPSS 0.00413 35th percentileScored 2026-11-07
Fix Fixed discourse (discourse): 2.7.8, 2.8.0.beta4

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

VendorProductAffected versionsFixed inStatusSource
discoursediscoursebefore 2.7.8; 2.8.0.beta1 to before 2.8.0.beta42.7.8, 2.8.0.beta4Patch availableCNA
  • discourse Vendordiscourse Affected before 2.7.8; 2.8.0.beta1 to before 2.8.0.beta4 Fixed in 2.7.8, 2.8.0.beta4 Patch available CNA

CPE configurations NVD · 5

CPEVersionsRoleVendor
cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:*before 2.7.8Vulnerablediscourse
cpe:2.3:a:discourse:discourse:2.8.0:beta1:*:*:*:*:*:*2.8.0 beta1Vulnerablediscourse
cpe:2.3:a:discourse:discourse:2.8.0:beta2:*:*:*:*:*:*2.8.0 beta2Vulnerablediscourse
cpe:2.3:a:discourse:discourse:2.8.0:beta3:*:*:*:*:*:*2.8.0 beta3Vulnerablediscourse
cpe:2.3:a:discourse:discourse:2.8.0:beta4:*:*:*:*:*:*2.8.0 beta4Vulnerablediscourse
  • cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:* Versions before 2.7.8 Vulnerable ·discourse
  • cpe:2.3:a:discourse:discourse:2.8.0:beta1:*:*:*:*:*:* Versions 2.8.0 beta1 Vulnerable ·discourse
  • cpe:2.3:a:discourse:discourse:2.8.0:beta2:*:*:*:*:*:* Versions 2.8.0 beta2 Vulnerable ·discourse
  • cpe:2.3:a:discourse:discourse:2.8.0:beta3:*:*:*:*:*:* Versions 2.8.0 beta3 Vulnerable ·discourse
  • cpe:2.3:a:discourse:discourse:2.8.0:beta4:*:*:*:*:*:* Versions 2.8.0 beta4 Vulnerable ·discourse

Remediation

  • Fix · CNA discourse (discourse) Fixed in 2.7.8, 2.8.0.beta4

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-39161

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