CVE-2009-2372 in Drupal
Summary
by MITRE
Drupal 6.x before 6.13 does not prevent users from modifying user signatures after the associated comment format has been changed to an administrator-controlled input format, which allows remote authenticated users to inject arbitrary web script, HTML, and possibly PHP code via a crafted user signature.
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Analysis
by VulDB Data Team • 07/27/2024
The vulnerability described in CVE-2009-2372 represents a critical security flaw in Drupal 6.x versions prior to 6.13 that stems from improper input validation and access control mechanisms within the comment and user signature handling subsystems. This issue specifically targets the administrative input format configuration process where users can modify their signatures even after the associated comment format has been altered by administrators to restrict certain input types. The flaw creates a scenario where authenticated users can exploit a time-of-check to time-of-use vulnerability by injecting malicious code into user signatures that persist even after administrators have changed the input format restrictions. This vulnerability directly maps to CWE-79 which describes Cross-Site Scripting (XSS) vulnerabilities, and CWE-94 which addresses Code Injection issues, making it particularly dangerous as it allows for both client-side and potentially server-side code execution depending on how the system processes the injected content.
The technical exploitation of this vulnerability occurs through a specific sequence where administrators modify comment formats to restrict user input to safe formats such as plain text or restricted HTML, but the system fails to validate or sanitize existing user signatures that were created before these restrictions were applied. When a user with appropriate privileges updates their signature after an administrator has changed the input format, the system does not properly validate whether the existing signature content complies with the new restrictions. This allows malicious users to inject HTML tags, javascript code, or even PHP code snippets that can execute in the context of other users' browsers when their signatures are displayed. The vulnerability is particularly insidious because it leverages the trust relationship between administrators and users, where administrators believe that their input format restrictions are properly enforced across all user content, including previously submitted signatures. The attack vector operates through the standard user profile management interface where users can edit their signatures, making it accessible to any authenticated user with appropriate permissions.
The operational impact of this vulnerability extends beyond simple XSS attacks and can potentially enable more severe exploitation techniques such as session hijacking, credential theft, or even remote code execution if the system processes user signatures through insecure PHP functions. Attackers can craft malicious signatures containing javascript payloads that steal cookies or redirect users to malicious sites, or they can inject PHP code if the system processes signatures in a context where PHP execution is possible. The vulnerability affects any Drupal installation running version 6.x before 6.13, particularly those with user-generated content features enabled, making it a widespread concern for organizations relying on older Drupal versions. The time window between when an administrator changes input format restrictions and when users update their signatures creates a window of opportunity for exploitation, and the lack of proper signature validation means that even users who have not explicitly updated their signatures can be affected if their content is displayed in contexts where the malicious code executes.
Organizations should immediately implement mitigations including upgrading to Drupal 6.13 or later versions where this vulnerability has been patched, implementing additional input validation for user signatures regardless of system configuration changes, and deploying content security policies to prevent script execution in user-generated content areas. The fix implemented in Drupal 6.13 addresses this issue by ensuring that user signatures are properly validated against current input format restrictions whenever they are modified, regardless of when the signature was originally created. Security teams should also consider implementing web application firewalls that can detect and block suspicious signature content patterns, and conduct regular audits of user-generated content to identify potentially malicious submissions. This vulnerability demonstrates the importance of maintaining proper input validation throughout a system's lifecycle and highlights how seemingly minor configuration changes can create unexpected security vulnerabilities when not properly enforced across all existing content. The ATT&CK framework categorizes this as a code injection technique under T1059, and as a privilege escalation vector through user profile manipulation under T1078, making it a multi-faceted threat that requires comprehensive defensive measures across multiple security domains.