An issue was discovered in the CheckUser extension for MediaWiki through 1.35.2. MediaWiki usernames with trailing whitespace could be stored in the cu_log database table such that denial of service occurred for certain CheckUser extension pages and functionality. For example, the attacker could turn off Special:CheckUserLog and thus interfere with usage tracking.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-31553
• https://gerrit.wikimedia.org/r/c/mediawiki/extensions/CheckUser/+/666963
• https://gerrit.wikimedia.org/r/c/mediawiki/extensions/CheckUser/+/666964
• https://gerrit.wikimedia.org/r/c/mediawiki/extensions/CheckUser/+/667023
• https://gerrit.wikimedia.org/r/c/mediawiki/extensions/CheckUser/+/667024
• https://gerrit.wikimedia.org/r/c/mediawiki/extensions/CheckUser/+/667025
• https://gerrit.wikimedia.org/r/c/mediawiki/extensions/CheckUser/+/667027
• https://phabricator.wikimedia.org/T275669