What is JA4+ and Why Does It Matter?
Introduction
Threat analysts and researchers are continually seeking tools and methodologies to gain a clearer understanding of malicious activity. JA4+ is an innovative approach designed to enhance network traffic analysis and infrastructure characteristics, enabling security professionals to identify and respond to threats more efficiently.
For CISOs and organizational leaders, for your security teams, JA4+ represents a significant advancement in providing actionable insights while supporting the operational goals. This primer aims to explain the value of JA4+, delve into its functionality, and highlight its relevance to both analysts and researchers.
What is JA4+?
JA4+ is the collective name for a broad suite of network fingerprinting methods, which are designed to facilitate threat hunting, network characterization, and advanced traffic analysis. These techniques help security teams identify patterns and behaviors in encrypted and unencrypted traffic, enabling the detection of malicious activity or unusual behavior based on specific attributes.
Think of JA4+ as a collection of tools that recognize unique "handshakes" or interactions that different software, devices, or threat actors use when communicating online. This makes it possible to analyze traffic in greater detail—even when the content of communications is obscured by encryption, designed to uncover hidden patterns and behaviors in network communications.
The JA4+ suite enables analysis of everything from encrypted traffic, like TLS and SSH, to web activity and digital certificates, providing insights into both client and server interactions. It even measures timing between systems to detect anomalies and actively scans connections for unique identifiers. Together, these techniques give security teams a clearer view of network activity, helping them detect and investigate threats more effectively.
Both JA3 and JA4+ were created by John Althouse (Medium page here) and a team of passionate developers looking to solve the investigation and research challenges they saw.
For this primer, we’ll focus specifically on JA4 method of fingerprinting TLS (Transport Layer Security) client libraries based on the ClientHello packet during the initial handshake. This technique allows analysts to identify specific applications or malware communicating over TLS by analyzing unique attributes from this handshake process.
The Benefits of JA4
JA4 offers several key advantages that make it an essential tool for traffic analysis and threat detection:
John lists the primary advantages over JA3 as follows:
JA4 is now both human and machine-readable, so an analyst familiar with JA4 fingerprints can simply glance at one to get a good understanding of what's going on and if it looks unusual.
JA4 is designed to work with multiple protocols including QUIC, TLS over UDP, and DTLS.
JA4's delimited sections make it easy to investigate or ignore particular sections of a fingerprint as well as extensible so that JA4 can be extended in the future without invalidating previous fingerprints.
JA4 is actively maintained by FoxIO with an extensive and growing database of fingerprints freely available on ja4db.com.
What this leads to for analysts is:
Improved Accuracy: By capturing more nuanced fingerprints, JA4 enables a higher degree of precision in identifying malicious actors and anomalous traffic.
Enhanced Visibility: Analysts can uncover activity that might otherwise blend into the noise of encrypted traffic.
Scalability: JA4 integrates seamlessly into existing workflows, making it adaptable for organizations of all sizes.
Efficiency in Investigations: Faster identification of malicious entities reduces time spent on triage and analysis.
JA4 vs. JA3: What Sets It Apart?
While JA3 laid the groundwork for TLS fingerprinting, JA4 introduced several enhancements. It builds on the principles of JA3—a technique that fingerprints the TLS ClientHello by hashing specific fields—but focuses on unique variations that improve precision in identifying threats. JA4 refines this approach, addressing some of the gaps in existing methodologies while providing enhanced utility for modern threat landscapes.
Deeper Insights: JA4 captures additional details from the handshake process, offering a richer dataset for analysis.
Refined Fingerprints: By addressing limitations in JA3’s methodology, JA4 improves accuracy in distinguishing between benign and malicious traffic.
Broader Applicability: JA4 is designed to align better with modern encryption protocols and evolving threat tactics.
How JA4 Helps Analysts and Researchers
For analysts and researchers, JA4 is a game-changer in threat intelligence, offering unparalleled visibility into network activity. While JA4 often identifies the underlying libraries used to build malware—rather than the malware itself—its precision in detecting malicious behaviors remains a critical advantage.
Here’s how JA4 and the broader JA4+ suite can be applied effectively:
Unmasking Malware Traffic: By leveraging JA4 fingerprints, analysts can detect specific tools or libraries that malware relies on, even when adversaries attempt to obscure their activity with encryption. The JA4+ suite reduces false positives by combining multiple fingerprints—up to 7 per connection—to ensure high-fidelity identification of malware or applications.
Behavioral Analysis: JA4 enables analysts to associate unique fingerprints with specific adversary behaviors, offering deep insights into how threat actors operate.
Threat Hunting: The combination of JA4+ fingerprints allows analysts to proactively identify suspicious patterns in network traffic, reducing dwell time for threats and improving detection accuracy.
In some cases, JA4 alone can be the "silver bullet" that unmasks malware with stunning precision
Example Use Case:
A malware sample uses a unique JA4 fingerprint during its encrypted communication with a command-and-control server. Analysts can flag and track this fingerprint across their network, identifying other compromised systems or attempts at infiltration.
Technical Overview: Understanding JA4
JA4 works by hashing specific fields from the TLS ClientHello message, such as:
Cipher suites
Extensions
Signature Algorithms
Other handshake attributes
These hashed fields create a unique identifier or "fingerprint" that can be matched against known malicious or benign traffic patterns. JA4’s refined approach allows it to capture subtler variations, making it particularly effective in identifying evolving threats.
Unlike JA3, which may occasionally group benign and malicious traffic under the same fingerprint, JA4 introduces additional granularity, reducing false positives and improving detection rates.
Conclusion: A Powerful Tool for Threat Analysts
JA4 is more than just an evolution in TLS fingerprinting—it’s a crucial asset for any security team seeking to strengthen its investigative capabilities. By providing precise, actionable insights into encrypted traffic, JA4 empowers analysts to stay ahead of adversaries and protect their organizations more effectively.
JA4 is set to become an indispensable part of the threat intelligence toolkit, with support from major platforms like CloudFlare and AWS.
Stay tuned for further updates as we continue to advance the capabilities of the cybersecurity community.