Web security is constantly evolving, and as attackers become more sophisticated, defenders need better tools to identify and mitigate threats.
One such tool gaining traction in the cybersecurity world is JA4 fingerprinting.
What Is JA4 Fingerprinting?
JA4 is a TLS fingerprinting method developed to help detect and track clients based on their TLS handshake behavior. It builds upon previous methods like JA3 (used for TLS Client Hello) but offers a more robust and accurate fingerprint by incorporating additional elements of the TLS negotiation.
Instead of relying on user-agent strings or IP addresses (which are easily spoofed), JA4 looks at low-level network behavior that is much harder to fake. This makes it a valuable tool for identifying malicious bots, malware, or scanners that may disguise themselves as legitimate traffic.
What Does JA4 Do?
JA4 creates a unique fingerprint for each client based on:
- Cipher suites
- TLS versions
- Extensions
- ALPN (Application-Layer Protocol Negotiation)
- TCP-level data
This fingerprint can be used to:
- Detect stealthy bots and crawlers
- Track evasive malware
- Identify known threat actor tools
- Enforce device reputation policies
How JA4 Helps a WAF
Web Application Firewalls (WAFs) traditionally rely on IP addresses, user-agent strings, or signature-based rule sets to block malicious requests. However, advanced attackers often rotate IPs and fake headers, making these techniques less effective.
With JA4 fingerprinting, WAFs gain a new, deeper layer of visibility. They can:
- Correlate malicious activity to TLS fingerprints, even across changing IPs
- Apply custom rules based on client behavior, not just request content
- Block or challenge suspicious fingerprints before the attack even reaches the application
In short, JA4 enhances a WAF’s ability to distinguish real users from evasive attackers — with far fewer false positives.
Which WAFs Support JA4?
Currently, a few open-source and commercial tools have begun integrating JA4 or similar TLS fingerprinting techniques. Some examples include:
- Suricata (via JA3/JA4 support for threat detection)
- Zeek (used for passive network monitoring and forensics)
- Some custom mod_security deployments
- A few enterprise-grade WAFs (details often under NDA)
But adoption is still early — and the opportunity for more powerful integrations is growing.
JA4 Fingerprinting Is Coming to SafeLine WAF
SafeLine will include built-in JA4 fingerprinting support soon. This will allow users to:
- Identify suspicious clients at the TLS level
- Write access control rules based on fingerprints
- Combine JA4 with our existing rate limiting, anti-bot, and CTI features for much stronger protection
With JA4, SafeLine will be able to detect and respond to threats before they interact with your web application — giving defenders more precision and flexibility than ever.
Stay tuned for the release — and join our Discord or follow us on X(https://x.com/safeline_waf) for the latest updates!
More resources:
SafeLine Website: https://ly.safepoint.cloud/ShZAy9x
Live Demo: https://demo.waf.chaitin.com:9443/statistics
Doc: https://docs.waf.chaitin.com/en/home
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