CVE-2011-1271 in .NET Framework
Summary
by MITRE
The JIT compiler in Microsoft .NET Framework 3.5 Gold and SP1, 3.5.1, and 4.0, when IsJITOptimizerDisabled is false, does not properly handle expressions related to null strings, which allows context-dependent attackers to bypass intended access restrictions, and consequently execute arbitrary code, in opportunistic circumstances by leveraging a crafted application, as demonstrated by (1) a crafted XAML browser application (aka XBAP), (2) a crafted ASP.NET application, or (3) a crafted .NET Framework application, aka ".NET Framework JIT Optimization Vulnerability."
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Analysis
by VulDB Data Team • 06/02/2025
The vulnerability identified as CVE-2011-1271 represents a critical security flaw in the Just-In-Time compilation mechanism of Microsoft .NET Framework versions 3.5 Gold and SP1, 3.5.1, and 4.0. This issue specifically manifests when the IsJITOptimizerDisabled configuration parameter is set to false, creating a condition where the JIT compiler fails to properly process expressions involving null string references. The flaw exists at the core of the runtime execution environment and demonstrates how optimization routines can introduce security weaknesses when not properly validated against malicious input patterns. The vulnerability operates under the Common Weakness Enumeration category CWE-129, which addresses improper validation of array indices and related memory access issues that can lead to privilege escalation and code execution.
The technical exploitation of this vulnerability occurs through carefully crafted applications that manipulate null string expressions during JIT compilation. When the JIT compiler processes these malformed expressions, it can cause unpredictable behavior that allows attackers to bypass access controls that would normally prevent code execution. The attack vectors include XAML browser applications, ASP.NET applications, and standard .NET Framework applications, each representing different execution contexts where the vulnerable JIT optimization can be triggered. The vulnerability's context-dependent nature means that successful exploitation requires specific environmental conditions and crafted input that can be delivered through malicious applications. According to MITRE ATT&CK framework, this vulnerability maps to T1059.001 (Command and Scripting Interpreter: PowerShell) and T1068 (Exploitation for Privilege Escalation) techniques, as it enables arbitrary code execution through legitimate runtime mechanisms.
The operational impact of this vulnerability extends beyond simple code execution to include potential privilege escalation and system compromise. Attackers can leverage this flaw to execute malicious code with the privileges of the affected application, potentially leading to full system compromise if the application runs with elevated permissions. The vulnerability's exploitation requires an attacker to craft specific applications that can trigger the JIT optimization path with malicious null string expressions, making it a sophisticated attack vector that requires understanding of both the .NET runtime internals and application development patterns. The affected systems include Windows operating systems running the specified .NET Framework versions, with the risk being particularly high in server environments where ASP.NET applications are commonly deployed and may be exposed to untrusted input. Organizations must consider this vulnerability as part of their broader security posture, particularly in environments where .NET applications are used extensively.
Mitigation strategies for CVE-2011-1271 should focus on both immediate remediation and long-term architectural improvements. The primary recommendation involves applying Microsoft security patches that address the JIT compiler optimization flaw, while also implementing runtime configuration changes that disable JIT optimization when possible. Organizations should consider setting IsJITOptimizerDisabled to true in application configuration files to prevent exploitation, though this may impact application performance. Network segmentation and application whitelisting can provide additional defense-in-depth layers, while monitoring for unusual JIT compilation patterns or suspicious application behavior can help detect potential exploitation attempts. Security teams should also implement regular vulnerability assessments targeting .NET Framework installations and ensure that all systems are updated to supported versions that do not contain this vulnerability. The remediation process should include thorough testing to ensure that disabling JIT optimization does not negatively impact legitimate application functionality, particularly in performance-critical environments where runtime optimization is essential for system operation.