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.

HTML::FormHandler versions before 0.410002 for Perl render field attributes into HTML without escaping using the process_attrs method. Any application with fields or field labels where some attributes are built from data rather than literals allows attacker-influenced text in an attribute value that can override the field attributes or embed JavaScript in rendered pages. For example, the RadioGroup widget uses the process_attrs method via the render_option and wrap_radio methods.

HTML::FormHandler versions before 0.410000 for Perl allow cross-site scripting via a submitted value rendered unescaped in an error message. The wrappers and renderers that emit a form's errors interpolate the error string straight into HTML with no escaping. Two of the library's own messages, no_match and not_allowed, splice the submitted value into that string, and a failing type constraint puts the rejected value into the message it builds, which _apply_actions hands to add_error. A field declared with a check regexp, a check list or a type constraint reaches those messages, with no custom validator and no non-default configuration. Errors rendered through an application's own escaping template layer rather than the library's rendering roles are not affected. A request over the network that submits markup to such a field gets it back live inside the error span, running script in the victim's origin. Re-rendering a rejected value later gives the stored variant.

HTML::FormHandler versions before 0.410002 for Perl render option group labels and radio button labels into HTML without escaping. The Select, RadioGroup, CheckboxGroup and HorizCheckboxGroup widgets render a group label unescaped, Select into a label attribute and the other three into element content. RadioGroup also renders each radio button's own label unescaped. Any application whose option list is built from data rather than literals, using options_from, an options_fieldname method, or the DBIC model, allows attacker-influenced text in a label that can override the options or embed JavaScript in rendered pages.