CVE-2012-4776 in .NET Framework
Summary
by MITRE
The Web Proxy Auto-Discovery (WPAD) functionality in Microsoft .NET Framework 2.0 SP2, 3.5, 3.5.1, 4, and 4.5 does not validate configuration data that is returned during acquisition of proxy settings, which allows remote attackers to execute arbitrary JavaScript code by providing crafted data during execution of (1) an XAML browser application (aka XBAP) or (2) a .NET Framework application, aka "Web Proxy Auto-Discovery Vulnerability."
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Analysis
by VulDB Data Team • 04/19/2021
The CVE-2012-4776 vulnerability represents a critical security flaw in Microsoft's .NET Framework that exploits the Web Proxy Auto-Discovery protocol implementation. This vulnerability specifically affects versions 2.0 SP2, 3.5, 3.5.1, 4, and 4.5 of the framework, creating a persistent risk across multiple generations of Microsoft's managed code execution environment. The flaw resides in the WPAD functionality which is designed to automatically discover proxy server configurations for web browsing, but fails to properly validate the configuration data received during this process. This validation failure creates a pathway for remote code execution through maliciously crafted proxy configuration data that can be injected during normal application operation.
The technical exploitation of this vulnerability occurs through two primary attack vectors that leverage the trust model inherent in the .NET Framework's proxy resolution mechanism. Attackers can craft malicious proxy configuration responses that contain embedded JavaScript code, which then executes within the context of the application process when the WPAD functionality attempts to resolve proxy settings. The first attack vector involves XAML Browser Applications (XBAPs) which are rich internet applications that run within web browsers and have elevated privileges due to their trusted execution context. The second vector targets standard .NET Framework applications that may be configured to automatically discover proxy settings, making any application using the framework potentially vulnerable regardless of its specific security posture.
The operational impact of this vulnerability extends far beyond simple code execution, as it enables attackers to gain arbitrary control over affected systems through a relatively simple attack methodology. The vulnerability can be exploited without requiring user interaction or specific system privileges, making it particularly dangerous in enterprise environments where .NET Framework applications are widely deployed. The attack can potentially lead to complete system compromise, data exfiltration, and lateral movement within networks where the vulnerable applications are running. This vulnerability is categorized under CWE-20 as "Improper Input Validation" and aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: JavaScript' which demonstrates how attackers can leverage script execution capabilities to gain persistent access to systems.
Organizations affected by this vulnerability should implement immediate mitigations including disabling WPAD functionality where possible, implementing proper network segmentation to limit proxy server access, and ensuring all affected .NET Framework versions are patched through Microsoft's security updates. The vulnerability highlights the importance of input validation in security-critical components and demonstrates how seemingly benign functionality can create dangerous attack surfaces when proper validation mechanisms are absent. Network administrators should also consider implementing proxy server monitoring and anomaly detection to identify potential exploitation attempts, while security teams should prioritize patching efforts across all affected systems to prevent exploitation attempts that could result in significant security breaches and data loss.