CVE-2026-19872 HTML::FormHandler versions before 0.410000 for Perl allow cross-site scripting via a submitted value rendered unescaped in an error message.
Attackers can execute arbitrary scripts in victim browsers by submitting malicious markup to form fields that trigger unescaped error messages.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-19872?
CVE-2026-19872 is a medium-severity cross-site scripting vulnerability, published on 8 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-79
Which versions are affected by CVE-2026-19872?
How do I fix CVE-2026-19872?
Upgrade to a fixed version.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-19872 being exploited?
There is no known exploitation of CVE-2026-19872 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-19872, GHSA-74pj-vp7j-2f6m, UBUNTU-CVE-2026-19872.