[mdev] - RtlUserFiberStart Shellcode execution in Rust - Printable Version +- Hack Forums (https://hackforums.net) +-- Forum: Tech (https://hackforums.net/forumdisplay.php?fid=444) +--- Forum: Coding (https://hackforums.net/forumdisplay.php?fid=151) +---- Forum: Software Development (https://hackforums.net/forumdisplay.php?fid=118) +---- Thread: [mdev] - RtlUserFiberStart Shellcode execution in Rust (/showthread.php?tid=6319090)

[mdev] - RtlUserFiberStart Shellcode execution in Rust - CL1B - Feb 4, 2026 Executing shellcode using RtlUserFiberStart in Rust Yeehaw! Shellcode execution in Rust using RtlUserFiberStart. Manipulates TEB fiber structures to redirect execution flow through the fiber mechanism. Getting TEB Pointer TEB (Thread Environment Block) is accessible via gs:[0x30] on x64. We need this to manipulate fiber data. Resolving RtlUserFiberStart Get the address of RtlUserFiberStart from ntdll. This function is called when a fiber starts and reads execution address from fiber context. Setting HAS_FIBER_DATA Bit in TEB TEB has a flags field that indicates if the thread has fiber data. We set bit 2 (0b100) at offset 0x20 to make the system think we have valid fiber data. Allocating RWX Memory for Shellcode Allocate executable memory and copy shellcode into it. Creating Fake Fiber Data Allocate a fake fiber data structure on the heap. RtlUserFiberStart reads the execution address from offset 0x0A8 in the fiber context. Setting Fiber Data Pointer in TEB TEB stores the fiber data pointer at gs:[0x20]. point it to our fake fiber data. Executing via RtlUserFiberStart Call RtlUserFiberStart. It reads our fake fiber context, gets the RIP value, and jumps to it. Cleanup Free allocated memory after execution. AV Performance (Click to View) For educational purposes only