Time Travel Triage: An Introduction to Time Travel Debugging utilizing a .NET Process Hollowing Case Research

The prevalence of obfuscation and multi-stage layering in at the moment’s malware typically forces analysts into tedious and guide debugging periods. For occasion, the first problem of analyzing pervasive commodity stealers like AgentTesla isn’t figuring out the malware, however rapidly slicing by the obfuscated supply chain to get to the ultimate payload.

Unlike conventional reside debugging, Time Travel Debugging (TTD) captures a deterministic, shareable document of a program’s execution. Leveraging TTD’s highly effective information mannequin and time journey capabilities enable us to effectively pivot to the important thing execution occasions that result in the ultimate payload.

This publish introduces the entire fundamentals of WinDbg and TTD crucial to start out incorporating TTD into your evaluation. We show why it deserves to be part of your toolkit by strolling by an obfuscated multi-stage .NET dropper that performs course of hollowing.

What is Time Travel Debugging?

Time Travel Debugging (TTD), a know-how provided by Microsoft as a part of WinDbg, data a course of’s execution right into a hint file that may be replayed forwards and backwards. The skill to rapidly rewind and replay execution reduces evaluation time by eliminating the necessity to continuously restart debugging periods or restore digital machine snapshots. TTD additionally permits customers to question the recorded execution information and filter it with Language Integrated Query (LINQ) to seek out particular occasions of curiosity like module masses or calls to APIs that implement malware functionalities like shellcode execution or course of injection.

During recording, TTD acts as a clear layer that enables full interplay with the working system. A hint file preserves a whole execution document that may be shared with colleagues to facilitate collaboration, circumventing environmental variations that may have an effect on the outcomes of reside debugging.

While TTD presents important benefits, customers ought to pay attention to sure limitations. Currently, TTD is restricted to user-mode processes and can’t be used for kernel-mode debugging. The hint information generated by TTD have a proprietary format, that means their evaluation is basically tied to WinDbg. Finally, TTD doesn’t provide “true” time journey within the sense of altering this system’s previous execution stream; when you want to change a situation or variable and see a special final result, you could seize a wholly new hint as the present hint is a hard and fast recording of what occurred.

A Multi-Stage .NET Dropper with Signs of Process Hollowing

The Microsoft .NET framework has lengthy been widespread amongst risk actors for growing extremely obfuscated malware. These packages typically use code flattening, encryption, and multi-stage assemblies to complicate the evaluation course of. This complexity is amplified by Platform Invoke (P/Invoke), which supplies managed .NET code direct entry to the unmanaged Windows API, permitting authors to port tried-and-true evasion methods like process hollowing into their code.

Process hollowing is a pervasive and efficient type of code injection the place malicious code runs beneath the guise of one other course of. It is frequent on the finish of downloader chains as a result of the approach permits injected code to imagine the legitimacy of a benign course of, making it troublesome to identify the malware with primary monitoring instruments.

In this case examine, we’ll use TTD to research a .NET dropper that executes its last stage by way of course of hollowing. The case examine demonstrates how TTD facilitates extremely environment friendly evaluation by rapidly surfacing the related Windows API capabilities, enabling us to bypass the quite a few layers of .NET obfuscation and pinpoint the payload.

Basic evaluation is an important first step that may typically establish potential course of hollowing exercise. For occasion, utilizing a sandbox could reveal suspicious course of launches. Malware authors regularly goal reputable .NET binaries for hollowing as these mix seamlessly with regular system operations. In this case, reviewing course of exercise on VirusTotal exhibits that the pattern launches InstallUtil.exe (present in %windir%Microsoft.NETFramework). While InstallUtil.exe is a reputable utility, its execution as a toddler strategy of a suspected malicious pattern is an indicator that helps focus our preliminary investigation on potential course of injection.