Description
An issue was discovered in MediaWiki before 1.31.10 and 1.32.x through 1.34.x before 1.34.4. The non-jqueryMsg version of mw.message().parse() doesn't escape HTML. This affects both message contents (which are generally safe) and the parameters (which can be based on user input). (When jqueryMsg is loaded, it correctly accepts only whitelisted tags in message contents, and escapes all parameters. Situations with an unloaded jqueryMsg are rare in practice, but can for example occur for Special:SpecialPages on a wiki with no extensions installed.)
Remediation
References
Related Vulnerabilities
ZenCart Cross-Site Request Forgery (CSRF) Vulnerability (CVE-2011-4403)
MediaWiki Improper Privilege Management Vulnerability (CVE-2021-44857)
WordPress Plugin dsIDXpress IDX Multiple Unspecified Vulnerabilities (2.1.32)
MediaWiki Exposure of Sensitive Information to an Unauthorized Actor Vulnerability (CVE-2021-31549)