Kernel

DirectComposition introduction Microsoft DirectComposition is a Windows component that enables high-performance bitmap composition with transforms, effects, and animations. Application developers can use the DirectComposition API to create visually engaging user interfaces that feature rich and fluid animated transitions from one visual to another.[1] DirectComposition API provides COM interface via dcomp.dll, calls win32kbase.sys through win32u.dll export function, and finally sends data to client program dwm.exe (Desktop Window Manager) through ALPC to complete the graphics rendering operation: ...

CVE-2021-1732 is a 0-Day vulnerability exploited by the BITTER APT organization in one operation which was disclosed in February this year[1][2][3]. This vulnerability exploits a user mode callback opportunity in win32kfull module to break the normal execution flow and set the error flag of window object (tagWND) extra data, which results in kernel-space out-of-bounds memory access violation. Root cause analysis The root cause of CVE-2021-1732 is: In the process of creating window (CreateWindowEx), when the window object tagWND has extra data (tagWND.cbwndExtra != 0), the function pointer of user32!_xxxClientAllocWindowClassExtraBytes saved in ntdll!_PEB.kernelCallbackTable (offset+0x58) in user mode will be called via the nt!KeUserModeCallback callback mechanism, and the system heap allocator (ntdll!RtlAllocateHeap) is used to allocate the extra data memory in user-space. By hooking user32!_xxxClientAllocWindowClassExtraBytes function in user mode, and modifying the properties of the window object extra data in the hook function manually, the kernel mode atomic operation of allocating memory for extra data can be broken, then the out-of-bounds read/write ability based on the extra data memory is achieved finally. ...