Auth bypass in Discourse

CVE-2026-21865

Discourse is an open source discussion platform. In versions prior to 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0, moderators can convert some personal messages to public topics when they shouldn't have access. This issue is patched in versions 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0. As a workaround, site admin can temporarily revoke the moderation role from untrusted moderators or remove the moderator group from the "personal message enabled groups" site setting until the Discourse instance has been upgraded to a version that has been patched.

Vulnerability class: Broken Access Control

Published · last modified .

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N.

EPSS exploit prediction

EPSS: 0.003 (15.8th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 16th percentile — 15.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-21865: held from 0.002 to 0.003.

EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.000

Affected products

  • Discourse — versions >= 2026.1.0-latest, < 2026.1.0, >= 2025.12.0-latest, < 2025.12.1, < 3.5.4

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-21865?
CVE-2026-21865 is a medium-severity vulnerability in Discourse, classified under Missing Authorization. CVSS score: 6.5/10. Published 2026-01-28.
How severe is CVE-2026-21865?
Medium severity. CVSS v3 base score is 6.5 out of 10.