CVE-2026-35198 in HeyForm
Summary
by MITRE • 07/20/2026
HeyForm is an open-source form builder. Prior to version 3.0.0-rc.7, a stored cross-site scripting (XSS) vulnerability in the form builder allows a low-privileged team member to inject malicious JavaScript that executes when a team owner views the form, leading to complete account takeover through privilege escalation. Version 3.0.0-rc.7 contains a patch for the issue.
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Analysis
by VulDB Data Team • 07/20/2026
The HeyForm platform presents a critical stored cross-site scripting vulnerability that demonstrates how seemingly minor security flaws can escalate into complete system compromise. This vulnerability affects versions prior to 3.0.0-rc.7 and specifically targets the form builder component where user input is not properly sanitized before being rendered back to other users. The flaw exists in the way the application processes and displays form data, creating an environment where malicious JavaScript code can be persistently stored within the system and subsequently executed when authorized users access the affected forms.
The technical implementation of this vulnerability stems from inadequate input validation and output sanitization mechanisms within the form builder's data handling pipeline. When team members with lower privileges create or modify forms containing malicious script payloads, these scripts are stored in the application's database without proper encoding or filtering. This stored content is then retrieved and rendered to other users, including team owners, who typically possess higher privileges and administrative capabilities. The vulnerability classifies under CWE-79 as a classic stored XSS flaw where attacker-controlled input flows through the application into a web browser without proper validation or sanitization.
The operational impact of this vulnerability extends far beyond simple data theft or defacement. A low-privileged team member can exploit this weakness to execute arbitrary JavaScript code in the context of a team owner's browser session, potentially leading to complete account takeover. The privilege escalation aspect means that attackers can leverage this initial foothold to gain administrative control over entire user accounts and their associated resources. This represents a significant concern for collaborative platforms where multiple users with varying permission levels interact within shared workspaces.
Security practitioners should recognize this vulnerability as a prime example of how insufficient data sanitization can create persistent attack vectors within web applications. The ATT&CK framework categorizes this type of vulnerability under T1531 - Account Access Removal and T1078 - Valid Accounts, since it allows attackers to assume the identity and privileges of legitimate users. Organizations utilizing HeyForm should immediately implement patch management protocols to upgrade to version 3.0.0-rc.7 or later, while also conducting thorough security assessments of similar components within their application stack. Additionally, implementing content security policies and regular input validation checks can help prevent similar vulnerabilities from emerging in other parts of the system architecture.
The remediation process for this vulnerability requires comprehensive review of all user input handling mechanisms within the form builder functionality. Security teams must ensure that all dynamic content is properly escaped or encoded before storage and display, with particular attention to HTML, JavaScript, and URL encoding considerations. The patched version addresses the core issue by implementing stricter input validation and output sanitization routines that prevent malicious code from being stored or executed within the application's rendering pipeline. Organizations should also consider implementing automated security scanning tools that can detect similar patterns of insecure data handling during development and deployment cycles to prevent future occurrences of this class of vulnerability.