What is CVE-2026-31869?

CVE-2026-31869 is a medium-severity vulnerability in Discourse, classified under Information Disclosure. CVSS score: 4.3/10. Published 2026-03-20.

How severe is CVE-2026-31869?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Auth bypass in Discourse

CVE-2026-31869

Discourse is an open-source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, the ComposerController#mentions endpoint reveals hidden group membership to any authenticated user who can message the group. By supplying allowed_names referencing a hidden-membership group and probing arbitrary usernames, an attacker can infer membership based on whether user_reasons returns "private" for a given user. This bypasses group member-visibility controls. Versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 contain a patch. To work around this issue, restrict the messageable policy of any hidden-membership group to staff or group members only, so untrusted users cannot reach the vulnerable code path.

Vulnerability class: Information Disclosure

EPSS: 0.002 (7.7th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N.

Affected products

Discourse — versions = 2026.3.0-latest, >= 2026.2.0-latest, < 2026.2.1, >= 2026.1.0-latest, < 2026.1.2

Weakness classification (CWE)

References

security-advisories@github.com (x_refsource_CONFIRM, Mitigation, Vendor Advisory)

Frequently asked questions

What is CVE-2026-31869?: CVE-2026-31869 is a medium-severity vulnerability in Discourse, classified under Information Disclosure. CVSS score: 4.3/10. Published 2026-03-20.
How severe is CVE-2026-31869?: Medium severity. CVSS v3 base score is 4.3 out of 10.