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CVE-2026-63428 heyform CVE debrief

CVE-2026-63428 is a vulnerability in HeyForm, an open-source form builder. The `completeSubmission` function accepts a `hiddenFields` array from the submitter and stores it without validating the supplied `id`/`name` against the form's declared `form.hiddenFields` schema. This allows an anonymous form submitter to inject arbitrary key/value pairs, including potential XSS payloads, fake authorization metadata, and integration-relevant values, into the stored submission. These fields are then forwarded to every webhook integration registered on the form. The issue was patched in version 3.0.0-rc.9.

Vendor
heyform
Product
Unknown
CVSS
MEDIUM 5.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-20
Original CVE updated
2026-07-22
Advisory published
2026-07-20
Advisory updated
2026-07-22

Who should care

Users of HeyForm, especially those who use webhook integrations, should be aware of this vulnerability and take steps to protect themselves. This includes updating to version 3.0.0-rc.9 or later and reviewing their form configurations for potential vulnerabilities.

Technical summary

The `completeSubmission` function in HeyForm accepts a `hiddenFields` array from the submitter and stores it verbatim in `submission.hiddenFields` without validation. This allows an attacker to inject arbitrary key/value pairs into the stored submission, which can then be forwarded to webhook integrations. The issue is patched in version 3.0.0-rc.9, which adds validation for the supplied `id`/`name` against the form's declared `form.hiddenFields` schema.

Defensive priority

Medium

Recommended defensive actions

  • Update to version 3.0.0-rc.9 or later
  • Review form configurations for potential vulnerabilities
  • Monitor form submissions for suspicious activity
  • Implement additional security measures, such as input validation and sanitization
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review.
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented.
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The CVE record was published on 2026-07-20T16:17:06.680Z and last modified on 2026-07-20T17:18:21.297Z. The NVD entry is currently Unverified. The vulnerability has a CVSS score of 5.8 and a severity of MEDIUM.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-63428 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-63428

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-63428 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-63428

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.