CVE-2026-86834 in MetForm Plugin
Summary
by MITRE • 10/03/2026
The MetForm WordPress plugin before 4.3.1 does not properly restrict access to a debug file it writes to the web root on every form submission when its HubSpot Forms integration is enabled, allowing unauthenticated attackers to read upstream API response data, including correlation identifiers and cookies.
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Analysis
by VulDB Data Team • 10/03/2026
The vulnerability identified in MetForm versions prior to 4.3.1 represents a critical information disclosure flaw stemming from improper access controls on debug artifacts generated during plugin operation. Specifically, when the HubSpot Forms integration feature is enabled, the plugin writes diagnostic data to a file located directly within the web root directory of the WordPress installation. This design choice creates a significant security gap because files placed in the web root are typically accessible via standard HTTP requests unless explicitly protected by server configuration or access control mechanisms that were absent in this implementation. The debug file is created and updated on every form submission, ensuring its persistence and availability to any client capable of reaching the site's public-facing interface.
From a technical perspective, the core issue lies in the lack of authentication checks for reading these specific log files. While the plugin may restrict access to administrative functions or API endpoints through standard WordPress security measures, it fails to apply similar restrictions to static debug output files stored in publicly accessible directories. This oversight allows unauthenticated attackers to craft simple HTTP GET requests targeting the path of this debug file. By doing so, they can retrieve the contents without needing valid credentials or bypassing any complex authentication logic, effectively treating sensitive operational data as public information.
The impact of this vulnerability is substantial due to the nature of the data contained within the debug logs. The files capture upstream API response data resulting from interactions with HubSpot's services. This includes correlation identifiers and session cookies associated with the form submissions processed by the plugin. Correlation IDs can be leveraged by attackers to trace specific user activities or correlate disparate events across different systems, potentially aiding in more sophisticated attacks such as cross-site request forgery analysis or targeted phishing campaigns. Furthermore, exposure of cookies poses a severe risk; if these session tokens are not properly secured with flags like HttpOnly and Secure, they could be stolen via Cross-Site Scripting (XSS) vectors combined with this information leak, leading to account takeover scenarios where an attacker assumes the identity of legitimate users or administrators interacting with HubSpot through MetForm.
This vulnerability aligns closely with CWE-209, which describes the generation of error messages containing sensitive information that could be utilized by attackers to compromise software security. It also maps to ATT&CK technique T1530, Data from Local System, as it involves accessing files on a compromised or vulnerable system to gather intelligence for further exploitation. The exposure of internal identifiers and session tokens falls under the broader category of Information Exposure (CWE-200), which provides adversaries with valuable context about the application's architecture and active sessions.
Mitigation strategies must focus immediately on restricting access to these debug files until a patched version is deployed. Administrators should ensure that any log or debug directories are not served directly by web servers such as Apache or Nginx, often achieved through configuration directives like Require all denied in Apache or deny all in Nginx configurations for specific paths. Additionally, developers of the plugin must implement strict access controls on file generation and storage, ensuring that sensitive data is either logged to non-public locations with restricted permissions or stripped of identifiable information before being written to disk. Upgrading to MetForm version 4.3.1 or later resolves this issue by correcting the handling of debug files and enforcing proper access restrictions, thereby eliminating the attack vector for unauthenticated data retrieval.