CVE-2009-3651 in Browscap
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in the "Monitor browsers feature in Browscap before 5.x-1.1 and 6.x-1.1, a module for Drupal, allows remote attackers to inject arbitrary web script or HTML via the User-Agent HTTP header.
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Analysis
by VulDB Data Team • 01/22/2019
The vulnerability identified as CVE-2009-3651 represents a critical cross-site scripting flaw within the Browscap module for Drupal platforms. This security weakness affects versions prior to 5.x-1.1 and 6.x-1.1, where the Monitor browsers feature fails to properly sanitize user input from the User-Agent HTTP header. The vulnerability stems from insufficient input validation and output encoding mechanisms that allow malicious actors to inject arbitrary web scripts or HTML content into web pages viewed by other users. This flaw specifically targets the way the module processes browser identification data, which is typically derived from the User-Agent string sent by web browsers during HTTP requests.
The technical implementation of this vulnerability involves the Browscap module's failure to adequately filter or escape special characters present in the User-Agent header before storing or displaying this information within the web application context. When a malicious user submits a crafted User-Agent string containing script tags or other malicious HTML content, the module processes this input without proper sanitization. The vulnerability is classified as a classic reflected XSS attack vector since the malicious payload is executed when other users view pages that display the unfiltered User-Agent information. This type of vulnerability falls under CWE-79 which specifically addresses Cross-site Scripting flaws, and represents a direct violation of secure coding practices for input validation and output encoding.
The operational impact of this vulnerability extends beyond simple script injection, as it provides attackers with the capability to perform session hijacking, deface web applications, steal sensitive user information, or redirect users to malicious websites. Attackers can craft User-Agent strings containing malicious JavaScript that executes in the context of other users' browsers, potentially compromising their sessions or accessing sensitive data. The vulnerability is particularly dangerous in environments where the Browscap module is used to track browser compatibility or user agent information for analytics purposes. This allows attackers to exploit the flaw without requiring any special privileges or direct access to the system, making it a significant threat to Drupal installations that utilize this module. The attack surface is broad since User-Agent headers are automatically included with every HTTP request, making this a persistent threat vector.
Mitigation strategies for CVE-2009-3651 involve immediate patching of the Browscap module to versions 5.x-1.1 and 6.x-1.1 or later, which contain proper input sanitization and output encoding mechanisms. Organizations should also implement proper input validation at multiple layers of their web application architecture, including implementing Content Security Policy headers to limit script execution capabilities. The principle of least privilege should be enforced by ensuring that the Browscap module operates with minimal required permissions and that user input is properly escaped before being displayed in web contexts. Additionally, network-level filtering can be implemented to monitor and block suspicious User-Agent patterns, though this approach is less reliable than proper application-level fixes. The vulnerability demonstrates the critical importance of proper input validation and output encoding as outlined in the OWASP Top Ten and aligns with ATT&CK technique T1203 which covers Exploitation for Client Execution, emphasizing the need for robust web application security controls. Organizations should also conduct regular security assessments and maintain updated security patches to prevent exploitation of similar vulnerabilities in their Drupal installations and other web applications.