YARA Rules

YARA is a powerful tool often described as "the pattern matching swiss knife for malware researchers." It's not an analysis technique itself, but a tool that enables rule-based identification of files or memory regions based on textual or binary patterns. YARA works by defining rules. Each rule consists of:

• A strings section: Defines specific text strings (ASCII/Unicode) or hexadecimal byte patterns to search for.

• A condition section: A boolean expression that specifies the logic for a match (e.g., "find file containing string $a AND string $b", "find file containing any of strings $s*", "find file where filesize is > 1MB and string $c is present").

When YARA scans a target (a file, a directory, or a process memory space) and finds content that matches the strings and satisfies the condition of a rule, it reports a match based on the rule's identifier.

In screensharing and DFIR, YARA is used for:

• Hunting for Known Cheats/Malware: Create rules based on unique strings, code snippets, import hashes (imphashes), or metadata extracted from known cheat files or malware samples (using tools like HxD, DiE). Scan suspicious files or process memory with these rules.

• Classifying Files: Write rules to identify files with specific characteristics (e.g., packed executables based on section names or entropy, files requiring admin privileges, files containing specific API calls).

• Memory Scanning Integration: Integrate YARA scanning into memory analysis workflows. Tools like Volatility (yarascan plugin) and Velociraptor (yara() VQL function) allow applying YARA rules directly to memory dumps or live process memory to find injected code or memory-resident artifacts. Automated SS tools like Ocean and Golden have also implemented YARA for enhanced detection.

• Flexibility: YARA supports wildcards, case-insensitivity, regular expressions, and modules, allowing for the creation of highly specific and adaptable detection rules.

Using YARA effectively requires access to good rules (either publicly available like those from Florian Roth, community-sourced, or custom-developed) and understanding how to apply them to the right targets (files vs. memory). It serves as a powerful hunting tool to flag items warranting deeper investigation based on predefined patterns.