![]() When the kernel loads a driver, execution goes through nt!MmLoadSystemImage to nt!MmCreateSection and eventually to the nt!MiValidateImageHeader routine. They check that nt!g_CiEnabled is set to TRUE, that the appropriate callback is not NULL, and then call it. To use the callbacks, wrapper functions exist for each of them in ntoskrnl.exe. It, in turn, sets CI!g_CiOptions and fills the addresses of CI!CiValidateImageHeader, CI!CiValidateImageData, and CI!CiQueryInformation callbacks before returning to the kernel. At the operating system initialization phase, the kernel sets nt!g_CiEnabled and invokes CI!CiInitialize routine with a pointer to the nt!g_CiCallbacks structure to initialize CI.dll. Ntoskrnl.exe works with an additional kernel library, CI.dll (Code Integrity). DSE ImplementationĪn old blog post by j00ru, a security researcher from Google’s Project Zero, provides a high-level overview of Code Integrity implementation in Windows 7. In this blog, we share the results of our research - details of two more methods for DSE tampering and how defenders might cope with this matter as long as this attack surface hasn't been eliminated. This motivated us to look deeper into the issue. Obtaining a certificate is primarily a logistical obstacle but tampering, on the other hand, is purely a technical challenge.ĭespite the efforts Microsoft dedicated to address this issue in recent years and the range of solutions provided by them, there’s been a clear increase in cases of attacks leveraging the well-known DSE tampering method. To overcome these restrictions, attackers use valid digital certificates, either issued to them or stolen, or they disable DSE during runtime. Detecting whether an unsigned driver or system file is being loaded into the kernel, or whether a system file has been modified, possibly by malicious software that runs with administrative permissions, improves the security of the operating system. This is also referred to as Driver Signature Enforcement (DSE). On 圆4-based versions of Windows, kernel-mode drivers must be digitally signed and checked each time they are loaded into memory. Code Integrity is a threat protection feature first introduced by Microsoft over 15 years ago. ![]()
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