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."

References

• https://nvd.nist.gov/vuln/detail/CVE-2011-1271
• https://docs.microsoft.com/en-us/security-updates/securitybulletins/2011/ms11-044
• https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A12686
• http://stackoverflow.com/questions/2135509/bug-only-occurring-when-compile-optimization-enabled