nginx-ssl-ja3

nginx module for SSL/TLS ja3 fingerprint.

Description

This module adds to nginx the ability of new nginx variables for the TLS/SSL ja3 fingerprint.

For details about the ja3 fingerprint algorithm, check initial project.

This implementation excludes extension (41) "pre_shared_key" used in TLS1.3 and treat it as GREASE extension. This prevents the generation of 2 different fingerprints (one for the initial session handshake, another one for the session resumption).

Configuration

Directives

Revision 110 of chrome browser introduces TLS ClientHello extensions random permutation, which makes fingerprinting irrelevant with this browser (firefox is planning to do the same). Using JA3_SORT_EXT cc macro during nginx configure invocation (--with-cc-opt='-DJA3_SORT_EXT') configures the module to sort TLS extensions in the JA3 string. The resulting fincgerprint is not compliant anymore with the JA3 algorithm (at this time of writing), but allows to get back effectiveness of fingerprinting.

Variables

$http_ssl_ja3

The ja3 fingerprint string for a SSL connection for a HTTP server.

771,4865-4866-4867-49195-49199-49196-49200-52393-52392-49171-49172-156-157-47-53-10,0-23-65281-10-11-35-16-5-13-18-51-45-43-21,0-29-23-24,0

$http_ssl_ja3_hash

The ja3 fingerprint MD5 hash for a SSL connection for a HTTP server.

Example:

http {
    server {
        listen                 127.0.0.1:443 ssl;
        ssl_certificate        cert.pem;
        ssl_certificate_key    rsa.key;
        error_log              /dev/stderr debug;
        return                 200 "$time_iso8601\n\n$http_user_agent\n\n$http_ssl_ja3\n\n$http_ssl_ja3_hash\n";
    }
}

$stream_ssl_ja3

The ja3 fingerprint string for a SSL connection for a stream server.

$stream_ssl_ja3_hash

The ja3 fingerprint MD5 hash for a SSL connection for a stream server.

Example:

stream {
    server {
        listen                 127.0.0.1:12345 ssl;
        ssl_certificate        cert.pem;
        ssl_certificate_key    rsa.key;
        error_log              /dev/stderr debug;
        return                 "$time_iso8601\n\n$stream_ssl_ja3\n\n$stream_ssl_ja3_hash\n";
    }
}

Build

Dependencies

• OpenSSL - 3.3.2 (branch openssl-3.3.2)

The master version OpenSSL is required because this module fetches the extensions types declared at SSL/TLS Client Hello by using the new early callback SSL_CTX_set_client_hello_cb.

I was unable to find a way to get these values with the current versions of nginx and OpenSSL.

So, in order to, have the client extensions available for the fingerprint, we also need to apply a patch to the nginx code.

If you use, for development, the docker supplied in this repo, the patch is already applied. Check the Dockerfile of the dev image.

Patches

• nginx - save client hello extensions
• openssl - more tls extensions

Compilation and installation

Build as a common nginx module.

# Hack/patch openssl - to include more common extensions

$ patch  -p1 < /build/nginx-ssl-ja3/patches/openssl-3.extensions.patch

patching file include/openssl/tls1.h
...
patching file ssl/statem/extensions.c
...


# Hack/patch nginx

$ patch -p1 < /build/ngx_ssl_ja3/patches/nginx.latest.patch

patching file src/event/ngx_event_openssl.c
...
patching file src/event/ngx_event_openssl.h
...

# Configure

$ ./configure --add-module=/build/ngx_ssl_ja3 --with-http_ssl_module --with-stream_ssl_module --with-debug --with-stream

# Install

$ make && make install

Tests

Make sure that the lib directory for nginx-tests is available in the 't' directory.

$ TEST_NGINX_BINARY=/usr/local/nginx/sbin/nginx prove -v

Docker

Docker images and a docker compose file is available at the ./docker directory.

$ docker-compose up --build -d

Creating nginx-ssl-ja3

Contributors

@fooinha - author

Fair Warning

THIS IS NOT PRODUCTION ready.

So there's no guarantee of success. It most probably blow up when running in real life scenarios.