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.

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 MediaWiki before 1.35.9, 1.36.x through 1.38.x before 1.38.5, and 1.39.x before 1.39.1. There is XSS in Wikibase date formatting via wikibase-time-precision-* fields. This allows JavaScript execution by staff/admin users who do not intentionally have the editsitejs capability.

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. When installing with a pre-existing data directory that has weak permissions, the SQLite files are created with file mode 0644, i.e., world readable to local users. These files include credentials data.

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. E-Widgets does widget replacement in HTML attributes, which can lead to XSS, because widget authors often do not expect that their widget is executed in an HTML attribute context.

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. SpecialMobileHistory allows remote attackers to cause a denial of service because database queries are slow.