YARA rules are text-based rules that help security researchers find and classify malware and other files. Each rule has an optional strings section, such as text, hex or regular expressions, and a required condition that decides when a file matches. This e-book explains what YARA rules are and how researchers use them.
What You Will Find In This Book?
Find the answers to “What is” and “How to”
This e-book helps you to understand the YARA from the beginning. You can give an answer to the “What are the YARA Rules?”, ” How do security researchers use them?”, and all other questions.
Look all sides of the topic & enhance your capabilities
“Effective YARA Rules for Security Researchers” does not just include the 101 topics. This e-book looks around all sides of the topic and gives you all the knowledge about it.
Gain practical insights from Experts
Brandefense Research Team’s knowledge gives you real-world examples, practical insights, and best practices. The information presented here is designed to empower you to harness the full potential of YARA in your security research efforts.
What does the Effective YARA Rules for Security Researchers report cover?
The report is numbered BD2023071002 and is authored by the Threat Research Team. Its preface says it aims to guide researchers through creating effective YARA rules, with practical insights, best practices and real-world examples.
Chapters in the report
- Introduction: what YARA is, how it works, and why it matters for malware analysis.
- YARA syntax: the rule header, metadata and conditions, then strings, regular expressions and conditionals, then metadata and comments.
- Rule creation: how to create a rule, plus common templates for file type identification, malware family detection and exploit detection.
- Advanced capabilities: modular rules, variables and functions, rule chaining and multithreading.
- Rule optimization and performance.
- Testing and validation: testing on known malware and reducing false positives.
The five steps the report gives for creating a rule
- Define the purpose of the rule.
- Identify the indicators of compromise.
- Write the rule.
- Test it against known good and known bad files.
- Refine it based on the test results.
Performance tips the report lists
- Use specific and narrow conditions. The report warns that generic keywords like “malware” or “virus” are likely to return many false positives.
- Use plain strings instead of regular expressions where possible.
- Use the nocase modifier for case-insensitive matching.
- Use the offset modifier to skip irrelevant content.
Reducing false positives
The report suggests using multiple rules, adding conditions such as file size or the digital signature of the file, and keeping a whitelist of known legitimate files. It also advises testing rules on benign files before relying on them.
To see the rule language in practice, read the YARA project on GitHub and the YARA overview on Wikipedia.