What is CVE-2021-31556?

CVE-2021-31556 is a critical-severity vulnerability in MediaWiki, classified under Improper Validation of Specified Quantity in Input. CVSS score: 9.8/10. Published 2021-08-12.

How severe is CVE-2021-31556?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Vulnerability in MediaWiki

CVE-2021-31556

An issue was discovered in the Oauth extension for MediaWiki through 1.35.2. MWOAuthConsumerSubmitControl.php does not ensure that the length of an RSA key will fit in a MySQL blob.

Published 2021-08-12 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.016 (75.0th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 75th percentile — 75.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.016 · newest: 0.016 · change: 0.000

Affected products

MediaWiki
Fedoraproject Fedora — versions 33, 34, 35

Weakness classification (CWE)

CWE-1284 — Improper Validation of Specified Quantity in Input

References

phabricator.wikimedia.org/T277380 (Permissions Required, Vendor Advisory)
gerrit.wikimedia.org/r/q/I13ff0350a9a0a3cd5ab3e1f82dd0d8d9c13cf9e9 (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)
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)

Frequently asked questions

What is CVE-2021-31556?: CVE-2021-31556 is a critical-severity vulnerability in MediaWiki, classified under Improper Validation of Specified Quantity in Input. CVSS score: 9.8/10. Published 2021-08-12.
How severe is CVE-2021-31556?: Critical severity. CVSS v3 base score is 9.8 out of 10.