PortSwigger: six of eight popular SVG sanitizers bypassed, plus header-based XSS in Firefox
PortSwigger research tested eight widely used SVG sanitizers and bypassed six, and demonstrates that a response header can execute JavaScript in Firefox even when the response body is harmless XML. The techniques are reproducible and apply to any application that renders user-supplied SVG or sets content headers over sanitized output.
If your platform accepts SVG uploads for media or avatars, re-test your sanitizer against these bypasses and review Content-Type and header handling on file-serving routes rather than trusting the sanitized body alone.