CVE-2026-63429 in HeyForm
Summary
by MITRE • 07/20/2026
HeyForm is an open-source form builder. Prior to version 3.0.0-rc.9, `POST /api/upload` has no authentication guard, no global guard, no form-context validation, no `openToken` requirement, and no session cookie check. Any anonymous internet user can upload files (PDF, DOC/DOCX, XLS/XLSX, CSV, TXT, MP4, images, etc., up to 10 MB) and receive a permanent public URL on the HeyForm domain. The endpoint is used by both authenticated form creators and unauthenticated form submitters; because no form-context binding exists, every request to it is anonymously accepted. Version 3.0.0-rc.9 contains a patch for the issue.
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Analysis
by VulDB Data Team • 07/20/2026
The vulnerability in HeyForm's file upload functionality represents a critical security flaw that undermines the platform's access control mechanisms and data integrity measures. This issue affects versions prior to 3.0.0-rc.9 where the POST /api/upload endpoint operates without any authentication guards, global protection mechanisms, or form-context validation. The absence of proper access controls creates an exploitable pathway where any anonymous internet user can bypass authentication requirements and upload various file types including documents, spreadsheets, presentations, text files, images, and video content up to 10 MB in size. The vulnerability stems from the lack of session cookie verification and the absence of openToken requirements, which are fundamental security measures that should prevent unauthorized file uploads.
The technical implementation flaw allows attackers to directly access the upload endpoint without proper authorization, eliminating any form of context binding between the upload request and the specific form it should belong to. This design oversight means that the system accepts all requests to the upload endpoint regardless of whether they originate from legitimate authenticated users or anonymous parties. The lack of form-context validation creates a scenario where uploaded files can be associated with any form within the system, potentially leading to data leakage, storage abuse, and unauthorized content distribution. According to CWE-306, this represents a missing authentication vulnerability where security-critical functions are accessible without proper authentication, while the absence of proper access control mechanisms aligns with CWE-284 which addresses improper access control in software systems.
The operational impact of this vulnerability is significant as it enables unauthorized file uploading on the HeyForm domain, resulting in permanent public URLs for all uploaded content. This creates potential risks including malicious file deployment, storage denial of service attacks, and unauthorized data exposure. Attackers can leverage this vulnerability to upload harmful content such as malware, phishing materials, or inappropriate files that become permanently accessible via the platform's public URLs. The system's inability to distinguish between legitimate form submissions and unauthorized uploads creates a persistent security risk that affects all users who rely on HeyForm for form creation and data collection. From an ATT&CK framework perspective, this vulnerability maps to T1195.001 (Phishing with Spoofed Credentials) and T1078.004 (Valid Accounts: Cloud Accounts) where attackers can abuse the system's lack of proper access controls to achieve unauthorized file operations.
The mitigation strategy involves implementing comprehensive authentication checks, session validation, and form-context binding for all upload requests. Version 3.0.0-rc.9 addresses this issue through proper security patches that establish required authentication guards, global protection mechanisms, and form-specific validation checks. Organizations using HeyForm should immediately upgrade to the patched version and implement additional monitoring of file upload activities to detect any unauthorized usage patterns. The fix ensures that only authenticated users with proper session tokens can access the upload endpoint, and all requests must be properly contextualized within specific forms to prevent cross-form file associations. This remediation aligns with industry best practices for secure file upload implementations as outlined in OWASP's secure coding guidelines and addresses fundamental security principles that should be enforced at every level of application architecture.