What is CVE-2021-31555?

CVE-2021-31555 is a high-severity vulnerability in MediaWiki, classified under Improper Input Validation. CVSS score: 7.5/10. Published 2021-04-22.

How severe is CVE-2021-31555?

High severity. CVSS v3 base score is 7.5 out of 10.

Improper input validation in MediaWiki

CVE-2021-31555

An issue was discovered in the Oauth extension for MediaWiki through 1.35.2. It did not validate the oarc_version (aka oauth_registered_consumer.oarc_version) parameter's length.

Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)

Published 2021-04-22 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.008 (55.1th percentile), scored 2026-10-07.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 55th percentile — 55.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: 0.000

Affected products

MediaWiki

Weakness classification (CWE)

CWE-20 — Improper Input Validation

References

phabricator.wikimedia.org/T277388 (Third Party Advisory)
gerrit.wikimedia.org/r/q/I222c053b4b14ac1ad0f5b3a51565b1b9cd4c139d (Issue Tracking, Vendor Advisory)

Frequently asked questions

What is CVE-2021-31555?: CVE-2021-31555 is a high-severity vulnerability in MediaWiki, classified under Improper Input Validation. CVSS score: 7.5/10. Published 2021-04-22.
How severe is CVE-2021-31555?: High severity. CVSS v3 base score is 7.5 out of 10.