What is CVE-2023-37303?

CVE-2023-37303 is a critical-severity vulnerability in MediaWiki, classified under Improper Check for Unusual or Exceptional Conditions. CVSS score: 9.8/10. Published 2023-06-30.

How severe is CVE-2023-37303?

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

Vulnerability in MediaWiki

CVE-2023-37303

An issue was discovered in the CheckUser extension for MediaWiki through 1.39.3. In certain situations, an attempt to block a user fails after a temporary browser hang and a DBQueryDisconnectedError error message.

Published 2023-06-30 · 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: 0.010 (59.9th percentile), scored 2026-10-01.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 60th percentile — 59.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.010 · newest: 0.010 · change: 0.000

Affected products

MediaWiki

Weakness classification (CWE)

CWE-754 — Improper Check for Unusual or Exceptional Conditions

References

phabricator.wikimedia.org/T338276 (Exploit, Patch, Issue Tracking, Vendor Advisory)
gerrit.wikimedia.org/r/q/I10a9273c542576b3f7bb38de68dcd2aa41cfb1b0 (Vendor Advisory)

Frequently asked questions

What is CVE-2023-37303?: CVE-2023-37303 is a critical-severity vulnerability in MediaWiki, classified under Improper Check for Unusual or Exceptional Conditions. CVSS score: 9.8/10. Published 2023-06-30.
How severe is CVE-2023-37303?: Critical severity. CVSS v3 base score is 9.8 out of 10.