CVE-2026-63428Public exploitNetwork attack vector

Unauthenticated stored-data injection via hidden-field submission

Published Jul 20, 2026 · Updated Jul 20, 2026

Improper input validation in HeyForm before 3.0.0-rc.9 allows remote attackers to inject arbitrary hidden-field data through form submissions. The completeSubmission resolver passes submitter-controlled hiddenFields directly into stored submission.hiddenFields instead of restricting identifiers and names to the form.hiddenFields schema. Anonymous access to an active form and its open token is sufficient; injected values persist in the owner-visible submission and propagate unchanged to configured webhooks.

CVSS severity5.8
Medium
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in HeyForm before 3.0.0-rc.9 allows remote attackers to inject arbitrary hidden-field data through form submissions. The completeSubmission resolver passes submitter-controlled hiddenFields directly into stored submission.hiddenFields instead of restricting identifiers and names to the form.hiddenFields schema. Anonymous access to an active form and its open token is sufficient; injected values persist in the owner-visible submission and propagate unchanged to configured webhooks.

The record

CVE
CVE-2026-63428
Published
Jul 20, 2026
Updated
Jul 20, 2026
Vendor
HeyForm
Product
HeyForm
Classifications
CWE-20, CWE-915, T1565.001, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 3.0.0-rc.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

HeyForm · HeyFormversion=< 3.0.0-rc.9

Published CVSS scores

5.8GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-20Improper Input Validation
CWE-915Improperly Controlled Modification of Dynamically-Determined Object Attributes
T1565.001Stored Data Manipulation
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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