CheckUser vulnerability

An issue was discovered in the CheckUser extension for MediaWiki through 1.39.3. Special:CheckUserLog shows usernames that have been hidden.

Published 14 Sep 2026Updated 14 Sep 20261 sources
CVSS 3.1

What happened

An issue was discovered in the CheckUser extension for MediaWiki through 1.39.3. Special:CheckUserLog shows usernames that have been hidden.

Affected versions

CheckUser: before 1.35.11 (semver); 1.36.0 through before 1.38.7 (semver); 1.39.0 through before 1.39.4 (semver) Fixed: See vendor advisory.

Why it matters

Review the vendor advisory and exposure of the affected product to determine operational impact.

Detection & mitigation

  • Apply vendor-provided updates or mitigations.
  • Review affected product exposure and access logs.

Public PoC references

No public PoC reference has passed the current publication threshold.