What is CVE-2021-30156?

CVE-2021-30156 is a medium-severity vulnerability in MediaWiki, classified under Information Disclosure. CVSS score: 4.3/10. Published 2021-04-09.

How severe is CVE-2021-30156?

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

Information disclosure in MediaWiki

CVE-2021-30156

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.

Vulnerability class: Information Disclosure

Published 2021-04-09 · last modified 2026-06-17.

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:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.011 (65.5th percentile), scored 2026-10-02.

Low probability of exploitation in the next 30 days, but still tracked. 65th percentile — 65.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.012 · newest: 0.011 · change: -0.000

Affected products

MediaWiki
Fedoraproject Fedora — versions 33, 34

Weakness classification (CWE)

CWE-200 — Information Disclosure

References

phabricator.wikimedia.org/T276306 (Exploit, Patch, Vendor Advisory)
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)

Frequently asked questions

What is CVE-2021-30156?: CVE-2021-30156 is a medium-severity vulnerability in MediaWiki, classified under Information Disclosure. CVSS score: 4.3/10. Published 2021-04-09.
How severe is CVE-2021-30156?: Medium severity. CVSS v3 base score is 4.3 out of 10.