CVE-2026-102615
Deferred Deferred - Pending Action

Stored XSS in HeyForm via Malicious File Upload

Publication date: 2026-11-05

Last updated on: 2026-11-05

Assigner: GitHub, Inc.

Description
HeyForm is an open-source form builder. Prior to 3.0.1, /api/upload accepts a file according to the client-controlled multipart file.mimetype while retaining an HTML filename, and static/upload serves the resulting file as text/html with contentSecurityPolicy: false. An ordinary user can therefore upload active HTML that executes on the HeyForm origin when a victim opens its returned URL. The same-origin script can access /graphql with the victim's session and read or modify data available to that account. The code also permits upload requests tied to an active public form through formId, openToken, and a fieldId belonging to a file or signature question, although the advisory did not fully verify that unauthenticated path end to end. This issue is fixed in version 3.0.1.

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Meta Information

Published
2026-11-05
Last Modified
2026-11-05
Generated
2026-11-05
AI Q&A
2026-11-05
EPSS Evaluated
N/A
NVD
CVE-2026-102615
EUVD
EUVD-2026-117549

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
heyform heyform < 3.0.1

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-79 The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

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Executive Summary

This is a stored cross-site scripting (XSS) vulnerability in HeyForm, an open-source form builder. The issue occurs because the application accepts file uploads with a client-controlled MIME type and serves HTML files as text/html without Content Security Policy (CSP) protection. Attackers can upload malicious HTML files disguised as images, which execute when accessed by victims. The vulnerability allows attackers to perform actions on behalf of users, such as accessing sensitive data via GraphQL queries.

Detection Guidance

Check HeyForm version for outdated installations. Inspect uploaded files in /static/upload for HTML content served as text/html without CSP. Monitor network traffic for unauthorized GraphQL requests from user sessions.

Impact Analysis

An attacker could trick you into opening a malicious HTML file uploaded to HeyForm. This could allow them to steal your session cookies, access your account data, or perform unauthorized actions like modifying forms or viewing sensitive information. The attack requires no admin privileges and can be triggered by unauthenticated users on public forms with file or signature fields.

Compliance Impact

This vulnerability could lead to unauthorized access to personal or sensitive data, violating GDPR and HIPAA requirements for data protection and confidentiality. Organizations using HeyForm may face compliance breaches if user data is compromised due to this XSS flaw.

Mitigation Strategies

Upgrade HeyForm to version 3.0.1 or later. Validate file content instead of trusting client headers. Implement CSP headers for uploaded files. Serve files with Content-Disposition: attachment.

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