What is CVE-2021-42040?

CVE-2021-42040 is a high-severity vulnerability in MediaWiki, classified under Loop with Unreachable Exit Condition (Infinite Loop). CVSS score: 7.5/10. Published 2021-10-06.

How severe is CVE-2021-42040?

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

Vulnerability in MediaWiki

CVE-2021-42040

An issue was discovered in MediaWiki through 1.36.2. A parser function related to loop control allowed for an infinite loop (and php-fpm hang) within the Loops extension because egLoopsCountLimit is mishandled. This could lead to memory exhaustion.

Published 2021-10-06 · 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:N/A:H.

EPSS exploit prediction

EPSS: 0.012 (65.9th percentile), scored 2026-10-01.

Low probability of exploitation in the next 30 days, but still tracked. 66th percentile — 65.9% 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: 0.012 · change: 0.000

Affected products

MediaWiki

Weakness classification (CWE)

CWE-835 — Loop with Unreachable Exit Condition (Infinite Loop)

References

phabricator.wikimedia.org/T287347 (Patch, Vendor Advisory)
gerrit.wikimedia.org/r/q/I0caf6f129f94612b5bcf406a171aa5ffedea1f80 (Patch, Vendor Advisory)

Frequently asked questions

What is CVE-2021-42040?: CVE-2021-42040 is a high-severity vulnerability in MediaWiki, classified under Loop with Unreachable Exit Condition (Infinite Loop). CVSS score: 7.5/10. Published 2021-10-06.
How severe is CVE-2021-42040?: High severity. CVSS v3 base score is 7.5 out of 10.