An issue was discovered in MediaWiki before 1.31.12 and 1.32.x through 1.35.x before 1.35.2.

published 2021-04-09 5 y ago modified 2026-06-17 4 mo ago also BIT-mediawiki-2021-30156 , EUVD-2021-17092

cvss: 4.3; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.1%; EPSS 1.1% chance of exploitation in 30 days, percentile 66%
public exploits: 0; none known

An issue was discovered in MediaWiki before 1.31.12 and 1.32.x through 1.35.x before 1.35.2. Special:Contributions can leak that a "hidden" user exists.

Patch / fix

fixed in 2 links 1

bitnami mediawiki 1.31.12, 1.35.2
mediawiki mediawiki 1.31.12, 1.35.2

phabricator.wikimedia.org/T276306 advisory

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-30156 updated 2025-11-21 cvss 5.4

mediawiki: Special: Contributions toolbar reveals existence of hidden users

Red Hat OpenShift Container Platform 3.11 mediawiki
affected: no fix planned “Will not fix”
Red Hat OpenShift Container Platform 4 mediawiki
affected: no fix planned “Out of support scope”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.14% chance of exploitation in the next 30 days, higher than 66% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

phabricator.wikimedia.org https://phabricator.wikimedia.org/T276306 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
NVD	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
NVD	2.0	4.0	AV:N/AC:L/Au:S/C:N/I:P/A:N
OSV	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
bitnami	mediawiki	<1.31.12 >=1.32.0, <1.35.2	1.31.12 1.35.2

Classification

Weakness

CWE-200 Exposure of Sensitive Information to an Unauthorized Actor

References

phabricator.wikimedia.org /T276306
exploit, patch, vendor-advisory, web
lists.fedoraproject.org /archives/list/package-announce%40lists.fedoraproject.org/message/26UJGHF7LJDOCQN6A3Z4PM7PYRKENJHE/
vendor-advisory, web
lists.fedoraproject.org /archives/list/package-announce%40lists.fedoraproject.org/message/2OMSV7B2TCFBOCICN3B4SMQP5HVRJQIT/
vendor-advisory, web
nvd.nist.gov /vuln/detail/CVE-2021-30156
web

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary