CVE-2026-16644 in Webform REST Plugin
Summary
by MITRE • 08/26/2026
Incorrect Authorization vulnerability in Drupal Webform REST allows Forceful Browsing. This issue affects Webform REST versions: from 0.0.0 to 4.1.0.
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Analysis
by VulDB Data Team • 08/26/2026
The identified security flaw resides within the Drupal Webform REST module, specifically affecting version ranges from 0.0.0 through 4.1.0. This vulnerability is classified as an incorrect authorization issue that facilitates forceful browsing, a technique often associated with insecure direct object references or broken access control mechanisms. In the context of web applications and content management systems like Drupal, REST APIs serve as critical interfaces for data exchange between clients and servers. When these endpoints lack proper validation of user permissions against the requested resources, they expose sensitive information to unauthorized actors. The core technical flaw involves a failure in the authorization logic that governs access to specific Webform submissions or configurations via the REST interface. Instead of verifying whether the authenticated user possesses the requisite privileges to view, modify, or delete particular form data, the module inadvertently allows any requester with valid credentials for the Drupal site to traverse and access resources intended for other users or administrative contexts.
This architectural deficiency enables attackers to perform forceful browsing attacks against the REST endpoints exposed by the Webform module. By systematically iterating through potential resource identifiers such as submission IDs or configuration keys, an attacker can retrieve private form submissions that may contain personally identifiable information, financial data, or confidential business communications. The impact extends beyond mere data leakage; it undermines the integrity and confidentiality guarantees provided by the application's security model. Since Webforms are frequently used to collect sensitive user input ranging from contact details to health-related inquiries, the exposure of this data can lead to significant privacy violations and regulatory non-compliance with standards such as GDPR or HIPAA depending on the jurisdiction and data type involved. Furthermore, if the REST endpoints allow for write operations without adequate checks, an attacker could potentially alter or delete form submissions, leading to denial of service or data integrity compromise.
From a classification perspective, this vulnerability aligns closely with CWE-284 Improper Access Control and CWE-639 Authorization Bypass Through User-Controlled Key. The ATT&CK framework categorizes such behaviors under T1078 Valid Accounts, where attackers leverage legitimate credentials to access resources they should not have permission to view or modify. It also relates to T1530 Data from Local System, as the attacker extracts data directly from the application's storage via unauthorized API calls. The severity of this issue is heightened by the widespread adoption of Drupal and its Webform module in enterprise environments where automated systems frequently interact with REST APIs for integration purposes. If these integrations rely on service accounts or tokens that are overly permissive, the blast radius of a successful exploitation increases significantly.
Mitigation strategies must prioritize immediate remediation through software updates. Administrators running affected versions should upgrade to Webform REST version 4.1.1 or later, where this authorization logic has been corrected to enforce strict access controls on all REST endpoints. In scenarios where upgrading is not immediately feasible due to compatibility constraints with other modules or custom code, temporary mitigations include restricting public exposure of the Drupal site's API routes via web server configuration rules such as Apache mod_rewrite or Nginx location blocks. Additionally, implementing a Web Application Firewall can help detect and block patterns consistent with forceful browsing attempts by monitoring for sequential access to resource identifiers that do not correspond to user-owned data. It is also advisable to audit existing REST permissions within the Drupal administrative interface to ensure that service accounts have only the minimum necessary privileges required for their specific functions, thereby reducing the attack surface available to potential exploiters.