CVE-2016-3165 in Drupal
Summary
by MITRE
The Form API in Drupal 6.x before 6.38 ignores access restrictions on submit buttons, which might allow remote attackers to bypass intended access restrictions by leveraging permission to submit a form with a button that has "#access" set to FALSE in the server-side form definition.
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Analysis
by VulDB Data Team • 10/05/2018
The vulnerability identified as CVE-2016-3165 represents a critical access control flaw within the Form API of Drupal 6.x systems prior to version 6.38. This issue stems from the improper handling of form button access restrictions, creating a pathway for remote attackers to circumvent intended security controls. The vulnerability specifically targets the server-side form definition mechanism where the "#access" property is used to control button visibility and usability, yet the system fails to enforce these restrictions during the form submission process.
The technical flaw manifests when a malicious actor exploits the Form API's handling of form elements by crafting a request that includes a submit button with "#access" set to FALSE in the form definition. Despite this explicit access restriction, the system processes the button submission without validating the access control, effectively allowing unauthorized users to execute actions they should not be permitted to perform. This represents a classic bypass vulnerability where client-side or server-side access controls are improperly enforced during form processing operations.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it can enable attackers to perform unauthorized actions within the Drupal application. Since the vulnerability operates at the form API level, it affects any functionality that relies on Drupal's form handling mechanisms, potentially allowing attackers to submit forms with restricted buttons, access administrative functions, or perform operations that should require specific user permissions. This vulnerability is particularly dangerous because it can be exploited without requiring authentication, making it a significant threat to Drupal 6.x installations.
The vulnerability aligns with CWE-284, which addresses improper access control, and can be mapped to ATT&CK technique T1078 for valid accounts and T1566 for social engineering through form manipulation. Organizations running affected Drupal 6.x systems face heightened risk of unauthorized access and potential system compromise. The vulnerability demonstrates a fundamental flaw in the application's security model where access control decisions made during form definition are not properly enforced during execution phases.
Mitigation strategies should prioritize immediate patching to Drupal 6.38 or later versions, which addresses the core access control bypass issue. Organizations should also implement additional security measures including thorough form validation, access control reviews, and monitoring for unauthorized form submissions. Network segmentation and application firewalls can provide additional defense-in-depth layers, while regular security assessments should verify that form access controls are properly enforced across all application components. The vulnerability highlights the importance of maintaining up-to-date software versions and the critical need for comprehensive security testing of form processing mechanisms in web applications.