An issue was discovered in MediaWiki before 1.35.9, 1.36.x through 1.38.x before 1.38.5, and 1.39.x before 1.39.1. CheckUser TokenManager insecurely uses AES-CTR encryption with a repeated (aka re-used) nonce, allowing an adversary to decrypt.

An issue was discovered in the CheckUser extension for MediaWiki through 1.39.x. Various components of this extension can expose information on the performer of edits and logged actions. This information should not allow public viewing: it is supposed to be viewable only by users with suppression rights.

Mediawiki 1.31 before 1.31.1 misses .htaccess files in the provided tarball used to protect some directories that shouldn't be web accessible.

An issue was discovered in the AbuseFilter extension for MediaWiki through 1.35.2. The page_recent_contributors leaked the existence of certain deleted MediaWiki usernames, related to rev_deleted.

An issue was discovered in the AbuseFilter extension for MediaWiki before 1.39.9, 1.40.x and 1.41.x before 1.41.3, and 1.42.x before 1.42.2. An API caller can match a filter condition against AbuseFilter logs even if the caller is not authorized to view the log details for the filter.

An issue was discovered in MediaWiki before 1.31.12 and 1.32.x through 1.35.x before 1.35.2. Blocked users are unable to use Special:ResetTokens. This has security relevance because a blocked user might have accidentally shared a token, or might know that a token has been compromised, and yet is not able to block any potential future use of the token by an unauthorized party.