Observable discrepancy in Discourse - CVE-2026-33425
Published: July 1, 2026
Vulnerability identifier: #VU136167
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-33425
CWE-ID: CWE-203
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Civilized Discourse Construction Kit, Inc.
Affected software:
Discourse
Discourse
Detailed vulnerability description
The vulnerability allows a remote attacker to infer private group membership or group existence.
The vulnerability exists due to observable discrepancy in the user directory exclude_groups parameter handling when processing directory requests with user-supplied exclude_groups values. A remote attacker can send crafted requests with the exclude_groups parameter and observe changes in directory results to infer private group membership or group existence.
How to mitigate CVE-2026-33425
Install security update from vendor's website.