YARA Rule
YARA is a framework introduced in 2007 to identify malware and classify it into families sharing similar characteristics, widely adopted among cybersecurity companies; a YARA rule is a set of patterns used to detect and match malicious files.
Introduced in 2007, YARA is a framework developed by Victor Manuel Alvarez to identify malware and classify it into families sharing similar characteristics.
Since then, it has become a widely adopted method among cybersecurity companies. At Sekoia.io, our cybersecurity researchers use YARA to continuously enhance our understanding of malware groups and update our Intelligence Center accordingly.
What exactly is a YARA rule? How does it work? And what are its main applications in cybersecurity (especially for analysts and researchers)?
Let's explore these questions in this article.
What is a YARA Rule and How Does It Work?
As mentioned above, YARA provides a language that describes a file through variables such as its size, the strings it contains, or fragments of compiled code.
Rules are created from information extracted from a malware sample or a group of related samples. Detection becomes possible through the similarity between the malware's strings and those of a known malware family.
Example: A YARA rule crafted by Sekoia.io's Threat Detection & Response (TDR) team.
During the identification and classification process, other data points are also considered:
File size
File type
Strings
Creation date and structural characteristics
By creating YARA rules based on multiple samples (often sourced from platforms like VirusTotal), cybersecurity analysts gain a key advantage — the ability to block malware before it executes on a network.
Because YARA rules analyze static files, they can detect threats without execution, making them both simple to use and extremely effective. This proactive capability explains YARA's growing popularity among cybersecurity researchers worldwide.
Detecting Malware and Enabling Continuous Threat Intelligence
YARA rules serve two main purposes in cybersecurity:
- Detection of malicious files
Security experts use YARA within tools like EDR (Endpoint Detection and Response).
Whenever a device creates or downloads a file, the rule automatically scans it and flags any resemblance to a known malware family. - Cyber Threat Intelligence (CTI) and malware tracking
CTI experts use YARA to catalog new malware variants and monitor their evolution.
Typically, analysts collect samples submitted by organizations to platforms like VirusTotal, focusing on those detected by existing YARA rules.
Once this dataset is built, they apply refined rules to identify malware variants — much like casting a fishing net to catch similar species.
This enables analysts to track the evolution of a malware family, its new technical behaviors, and even map its infrastructure, including the web servers it communicates with.
At Sekoia.io, our Cyber Threat Intelligence experts use similar procedures. For instance, one of our studies identified over 38,000 IP addresses used as Command & Control (C2) servers by ransomware groups in 2021 — a 75% increase compared to 2020.
These findings, analyzed and published by Sekoia.io's CTI experts, are available for free download through our blog.
Armed with this intelligence, researchers can then craft new YARA rules to detect previously unknown malware variants.
Clients of Sekoia.io's CTI platform gain access to this evolving knowledge, allowing them to detect and neutralize potential infections before they cause harm.
For example, if a client's system communicates with a web server linked to a YARA-detected malware sample, Sekoia.io can alert the organization before the threat impacts its network.
Beyond YARA: Complementary Rules such as Sigma and IDS
While YARA identifies malware based on its structure or code, other frameworks focus on different detection angles:
Sigma Rules
Sigma detects malware based on behavior — what it does when executed.
It flags any suspicious activity performed by a script or attacker by analyzing logs, i.e., records of system actions.
To create Sigma rules, analysts typically execute malware in a sandbox (isolated virtual environment) and log every action.
The resulting dataset describes in detail what the malware does, for instance:
Creates a file named "X" or "Y"
Adds a registry key "0000"
Modifies or deletes folder "Z"
Executes a specific command
These patterns become the basis for Sigma rules that detect future activity matching the same behavior.
IDS (Intrusion Detection System) Rules
IDS rules, such as Suricata, focus on how malware communicates.
They track network signatures — IP addresses, domains, or communication patterns used by malware to connect with its infrastructure.
Cybersecurity experts maintain signature libraries that trigger alerts when a network connection matches a known attacker's signature.
This allows real-time detection of suspicious communications between corporate networks and malicious infrastructure.
Conclusion
In this article, we explored the fundamentals of YARA rules, their role in malware detection, and their value in continuous cyber threat intelligence.
At Sekoia.io, our analysts and researchers rely on YARA to monitor the evolution of ransomware and other threats.
Through our CTI platform and XDR solution, we provide clients with contextualized, actionable intelligence to neutralize threats before execution within their environments.
If you're looking to proactively strengthen your information system security, Sekoia.io is a French cybersecurity vendor offering operational security platforms for CISOs, CIOs, analysts, engineers, and MSSPs.
Our XDR platform, CTI tools, and Threat Intelligence solutions enable users to detect, understand, and neutralize cyber threats — across any attack surface.
