In src/mistune/directives/admonition.py, the render_admonition() function concatenates the :class: option directly into the HTML class attribute without escaping (lines 63-68).
This allows attribute injection and XSS even when HTMLRenderer(escape=True) is used.
The directive name parameter is safe (validated against whitelist), but the class option comes from raw user input.
In
src/mistune/directives/admonition.py, therender_admonition()function concatenates the:class:option directly into the HTML class attribute without escaping (lines 63-68).This allows attribute injection and XSS even when
HTMLRenderer(escape=True)is used.The directive name parameter is safe (validated against whitelist), but the class option comes from raw user input.