CVE-2026-63428

5.8 MEDIUM 0.3% exploit odds Fix listed XSS

What it is

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.

At a glance

Exploitability: Can be exploited over the network without logging in. Limited direct impact.
Exploit odds: 0.3% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-07-20 16:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-07-22 20:50 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.3% in the next 30 days (EPSS).
Severity: 5.8 MEDIUM (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-07-20 16:17 UTC
Last modified: 2026-07-22 20:50 UTC
Exploit probability: 0.3% · EPSS, next 30 days
Weakness: CWE-20 · Improper input validation
Record status: Deferred

Attack profile CVSS 3.1 · 5.8

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None
Scope: Changed
Confidentiality: None
Integrity: Low
Availability: None

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-63428.md and follow it. Check whether this project is affected by CVE-2026-63428. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record