csrss.exe (Client Server Runtime Subsystem)

• Function: A critical, core Windows process responsible for managing console windows (like Command Prompt), creating and deleting threads, and handling parts of the graphical subsystem. Due to its low-level operations, its memory often contains logged paths of executed files (.exe) and loaded libraries (.dll).

• Accessibility Issues: As a protected system process, accessing csrss.exe memory often requires administrator privileges and the Kernel Mode Driver enabled in System Informer. Antivirus software can sometimes interfere, and access might be restricted on heavily locked-down systems or specific Windows builds. There are typically two instances of csrss.exe running.

• Filtering Logic (Multiple Instances): When analyzing the two csrss.exe instances:

  • For finding executed .exe files (with standard extensions), focus analysis on the instance with fewer private bytes.

  • For finding loaded/injected .dll files OR .exe files with spoofed/changed extensions, focus analysis on the instance with more private bytes.

• Common Search Patterns (Regex, case-insensitive):

  • ^[A-Z]:\\.+.exe$: Finds full paths ending specifically in .exe. Primarily used on the instance with fewer private bytes.

  • ^[A-Z]:\\.+.dll$: Finds full paths ending specifically in .dll. Primarily used on the instance with more private bytes. Crucial for detecting standard DLL injections. Pay close attention to unsigned DLLs found with this pattern.

  • ^(?:\\\\\?\\)?[A-Za-z]:\\.+$: A broader pattern to find full paths with any or no extension. Useful on the instance with more private bytes when searching for executables disguised with fake extensions (e.g., .tmp, .png) or extensionless files launched via specific methods. Can also help find DLLs.