Understanding MIME Type Sniffing Vulnerabilities

MIME type sniffing emerged as a browser feature to handle incorrectly configured servers that sent wrong Content-Type headers. While helpful for compatibility, this feature introduces serious security vulnerabilities. Attackers can upload malicious files disguised as harmless content types, relying on browser sniffing to execute them as scripts or other dangerous formats. This vulnerability particularly affects user-generated content platforms, file sharing services, and any application accepting file uploads.

The attack surface extends beyond obvious script execution. Browsers might interpret uploaded images containing embedded HTML as web pages, style sheets with embedded scripts as executable code, or text files with specific patterns as various executable formats. These misinterpretations can lead to cross-site scripting (XSS), privilege escalation, and data theft.