CVE-2009-0091 in Windows
Summary
by MITRE
Microsoft .NET Framework 2.0, 2.0 SP1, and 3.5 does not properly enforce a certain type-equality constraint in .NET verifiable code, which allows remote attackers to execute arbitrary code via (1) a crafted XAML browser application (XBAP), (2) a crafted ASP.NET application, or (3) a crafted .NET Framework application, aka "Microsoft .NET Framework Type Verification Vulnerability."
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Analysis
by VulDB Data Team • 09/18/2018
The vulnerability identified as CVE-2009-0091 represents a critical type verification flaw within Microsoft .NET Framework versions 2.0, 2.0 SP1, and 3.5. This security weakness stems from improper enforcement of type-equality constraints in .NET verifiable code, creating a pathway for malicious actors to bypass security mechanisms that should prevent arbitrary code execution. The vulnerability specifically affects the runtime verification process that ensures code integrity and type safety within the .NET environment, fundamentally undermining the security model that developers and administrators rely upon for application isolation and execution control.
The technical exploitation of this vulnerability occurs through three distinct attack vectors that leverage the flawed type verification mechanisms. Attackers can craft malicious XAML browser applications (XBAP) that exploit the type verification gap to execute unauthorized code within the security context of the victim's system. Additionally, malicious ASP.NET applications can be constructed to exploit the same vulnerability, allowing attackers to inject and execute arbitrary code within web application contexts. The third vector involves crafting malicious .NET Framework applications that take advantage of the type verification flaw to gain elevated privileges and execute malicious payloads. These attack methods exploit the fundamental assumption that .NET verifiable code should maintain strict type safety and prevent unauthorized code execution through the runtime type checking mechanisms.
The operational impact of this vulnerability extends beyond simple code execution, as it represents a complete breakdown in the .NET Framework's security model that could lead to full system compromise. When exploited, the vulnerability allows attackers to execute arbitrary code with the privileges of the affected application, potentially leading to complete system takeover. The implications are particularly severe in enterprise environments where .NET applications are extensively used, as attackers could leverage this vulnerability to move laterally through networks, escalate privileges, and access sensitive data. The vulnerability affects not just individual applications but the entire .NET runtime environment, making it a critical concern for organizations maintaining .NET-based infrastructure.
Organizations should implement multiple layers of defense to mitigate this vulnerability, beginning with immediate deployment of Microsoft security patches that address the type verification flaw in the .NET Framework. Network segmentation and application whitelisting can provide additional protection by limiting the attack surface and preventing unauthorized code execution. The vulnerability aligns with CWE-248, an unspecified flaw in the type verification process, and maps to ATT&CK technique T1059.001 for execution through .NET applications. Administrators should also consider implementing runtime monitoring solutions that can detect anomalous code execution patterns and behavior that might indicate exploitation attempts. Regular security assessments and code reviews focusing on .NET applications can help identify potential attack vectors that might leverage similar type verification weaknesses, ensuring comprehensive protection against both current and future exploitation attempts.
This vulnerability demonstrates the critical importance of runtime type verification in managed code environments and highlights the potential consequences when such mechanisms fail. The flaw represents a fundamental security weakness in the .NET Framework's security architecture that could be exploited to bypass multiple security controls. Organizations must maintain vigilant patch management processes and security monitoring to prevent exploitation of such critical vulnerabilities, particularly in environments where .NET Framework applications form a core component of business operations and infrastructure security.