CVE-2026-63428: Heyform

Medium severity, CVSS 5.8. EPSS: 0.3% chance of exploitation in the next 30 days.

HeyForm is an open-source form builder. Prior to version 3.0.0-rc.9, `completeSubmission` accepts a `hiddenFields: [{id, name, value}]` array from the submitter and stores it verbatim in `submission.hiddenFields`, without validating the supplied `id`/`name` against the form's declared `form.hiddenFields` schema. An anonymous form submitter can therefore inject arbitrary key/value pairs (including XSS payloads, fake authorization metadata, integration-relevant values) into the stored submission. These fields are subsequently forwarded as-is to every webhook integration registered on the form. Version 3.0.0-rc.9 contains a patch for the issue.

Affected products

• Heyform Heyform: before 3.0.0-rc.9 (fixed in 3.0.0-rc.9)

Published 2026-07-20. Last modified 2026-07-22.