# CVE-2026-63428: HeyForm improper input validation in hiddenFields submission

Source: https://junglewise.ai/threats/cve-2026-63428-heyform-improper-input-validation-in-hiddenfields-submission  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-20. Updated: 2026-07-20  
License: CC BY 4.0 with a link back

CVE-2026-63428 · Severity: medium · CVSS 5.8 · Published 2026-07-20

HeyForm is an open-source tool used to build and manage online forms. A security flaw allows anyone submitting a form to inject unauthorized data into "hidden fields" that are normally controlled by the form creator. This could allow attackers to bypass business logic, spoof administrative roles, or send malicious scripts to third-party services connected via webhooks, potentially compromising downstream systems or internal dashboards.

Technologies: [HeyForm](https://junglewise.ai/threats/technologies/heyform). Vendors: [HeyForm](https://junglewise.ai/threats/vendors/heyform).

## Quick answers

**Is CVE-2026-63428 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-63428 being exploited in the wild.

**How severe is CVE-2026-63428?** Medium severity, with a CVSS score of 5.8, published 20 July 2026.

**Which products and versions are affected?** HeyForm < 3.0.0-rc.9.

**Is there a fix for CVE-2026-63428?** A patch was published on 2026-06-25: Fix commit pushed to repository Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-63428 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-63428?** Check whether you run HeyForm at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The `completeSubmission` resolver in HeyForm accepts a `hiddenFields` array from the submitter and persists it to the database without validating the provided IDs or names against the form's `form.hiddenFields` schema. Because these fields are stored verbatim and subsequently forwarded to all registered webhook integrations, an anonymous attacker can perform webhook payload poisoning, XSS injection, or override legitimate metadata (such as UTM parameters or authorization roles). The vulnerability stems from improper input validation (CWE-20) and improperly controlled modification of object attributes (CWE-915). The issue is addressed in version 3.0.0-rc.9.

## Affected products

- HeyForm HeyForm < 3.0.0-rc.9

## Timeline

- 2026-06-25: patched: Fix commit pushed to repository
- 2026-07-01: advisory: GitHub Security Advisory published
- 2026-07-20: disclosed: CVE published to NVD

## References

- [https://github.com/heyform/heyform/commit/092e255e9e02565de1b3c057f3dad849160952d2](https://github.com/heyform/heyform/commit/092e255e9e02565de1b3c057f3dad849160952d2)
- [https://github.com/heyform/heyform/security/advisories/GHSA-r7vg-xh87-v4w3](https://github.com/heyform/heyform/security/advisories/GHSA-r7vg-xh87-v4w3)

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