# CVE-2026-63428: Business logic in heyform

> Attackers can inject arbitrary hidden fields into form submissions, bypassing validation and potentially triggering XSS or unauthorized actions in downstream integrations.

- **Severity:** Medium 5.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 20 Jul 2026
- **Updated:** 20 Jul 2026
- **Also known as:** GHSA-r7vg-xh87-v4w3

## What is CVE-2026-63428?

CVE-2026-63428 is a medium-severity vulnerability in heyform, published on 20 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-915 (Improperly Controlled Modification of Dynamically-Determined Object Attributes), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-63428?


## How do I fix CVE-2026-63428?

No fix has been published for CVE-2026-63428 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-63428 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-63428 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63428 and fix it if it is affected.

What it is: CVE-2026-63428 is a medium-severity vulnerability in heyform, published on 20 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-63428 exists.

Affected product: heyform. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-63428/ (Markdown: https://insights.sbomify.com/CVE-2026-63428/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63428
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63428
- OSV: https://osv.dev/vulnerability/CVE-2026-63428

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63428/
Summaries are generated and may contain mistakes; the official description above is the record.