HTML::FormHandler versions before 0.410002 for Perl render some error messages into HTML without escaping. The Table form layout and the Bootstrap 2 and 3 wrappers splice each error string straight into the surrounding markup. Version 0.410000, the fix for CVE-2026-19872, escaped the equivalent values in the other layouts and wrappers, and 0.410002 extended that to these three. Error messages that contain attacker-influenced content such as rejected field values could embed JavaScript in rendered pages.
https://metacpan.org/release/ABRAXXA/HTML-FormHandler-0.410002/changes
https://github.com/gshank/html-formhandler/commit/2ea9e138dbfe231e317c13936abe6583217c807f.patch