Hunt-Weird-Syscalls

This is a ETW based POC to monitor for abnormal syscalls.

For now, the syscalls NtOpenThread and NtSetContextThread are monitored to identify IOCs indicating both direct and indirect syscalls.

Description

This project uses ETW, more precisely kernel based ETW providers, to monitor for IOCs.
ETW providers sitting in the kernel can effectively be leveraged, as the calltraces of emitted events contain the usermode address from where the syscall was conducted.

This allows monitoring IOCs indicating direct and indirect syscalls, a technique often leveraged by threat actors:

1: A syscall was conducted from an untrusted module (=direct syscall)
2: The used syscall stub in ntdll does not match the conducted syscall (=indirect syscall)

This project uses the Provider: Microsoft-Windows-Kernel-Audit-API-Calls to monitor for OpenThread and SetContextThread events triggered by the syscalls NtSetContextThread or NtOpenThread respectively.
Calltraces are enabled, using the flag EVENT_ENABLE_PROPERTY_STACK_TRACE.

This is a POC, and only monitors two specific syscalls. It is of course possible to use other kernel based providers to enhance telemetry.

Tests

This project contains two sample programs using direct and indirect syscalls created using the amazing SysWhispers3. They were generated as follows:

python3 syswhispers.py -a x64 -m jumper_randomized --functions NtSetContextThread
python3 syswhispers.py -a x64 -m embedded --functions NtSetContextThread

Upon execution, abnormal syscalls should be identified:

Tested on 10.0.19044.

Credits

• KrabsETW
• SysWhispers3
• etw provider docs by repnz
• @OutflankNL for IsElevated()
• @trickster012 for testing and support <3