TLS MITM proxy for reverse-engineering purposes

Why

It is often necessary to decrypt TLS traffic when reverse-engineering applications. This can easily be done with tools like mitmproxy. However, server can detect such MITM attack due to mitmproxy's a very specific TLS fingerprint (think JA3 and other implementations). OpenSSL backend cannot be easily configured to mimic given fingerprint (if you know how to do it, please open issue and tell me). Servers can detect this and refuse connection or disallow access (for example, Cloudflare often does this).

What

This tool is written to address these problems using awesome utls library. For software under test (SUT) it looks like a usual HTTP proxy. When SUT connects through it, ClientHello is fingerprinted and upstream connection with the same fingerprint is established. Data inside TLS tunnel are not modified so higher-level fingerprints (like HTTP/2 fingerprint from Akamai) are also preserved. Both client and upstream connections` TLS keys are logged so tools like Wireshark can be used to record and inspect traffic passively.

--------------           ---------------           --------------          --------------
|  Software  |           |   Mirror    |           |  Upstream  |          |   Remote   |
|   under    |<----+---->|   proxy     |<----+---->|   proxy    |<-------->|   Server   |
|   test     |     |     | (this tool) |     |     | (optional) |          |            |
--------------     |     ---------------     |     --------------          --------------
                   |           |             |
       +-----------+-----------)-------------+
       |                       |
       v                       v
--------------           ---------------
|  Sniffer   |           |   TLS key   |
| (Wireshark)|<----------|    log      |
|            |           |    file     |
--------------           ---------------

How

This tool only logs encryption keys and does not record traffic. You need a sniffer. Wireshark has been tested, so instruction assumes it is used.

1. Generate and install root certificate for next step (cert.pem and key.pem)
2. Start proxy (./mirror_proxy -c cert.pem -k key.pem -s sslkeylogfile.log)
3. Configure TLS decryption in Wireshark using sslkeylogfile.log
4. Start traffic capture
5. Configure SUT to use proxy
6. Start SUT and begin looking at packets

Proxy can connect to target server through another proxy (-p, HTTP(S) and SOCKS5 are supported). Additionally, you can disable decryption completely (-m passthrough) - all connection data will be forwarded unaltered.

What else

Installation:

go install github.com/fedosgad/mirror_proxy@latest

Manual build and run:

git clone https://github.com/fedosgad/mirror_proxy
cd mirror_proxy/
go build

then

./mirror_proxy -h

or (this automatically uses certificate and key from installed mitmproxy)

./mirror.sh -h

CLI usage:

$ ./mirror_proxy -h
Usage: cmd [FLAG]...

Flags:
    --verbose, -v           Turn on verbose logging                                   (type: bool; default: false)  
    --listen, -l            Address for proxy to listen on                            (type: string; default: :8080)
    --pprof                 Enable profiling server on http://{pprof}/debug/pprof/    (type: string)
    --mode, -m              Operation mode (available: mitm, passthrough)             (type: string; default: mitm) 
    --dial-timeout, -dt     Remote host dialing timeout                               (type: string; default: 5s)   
    --proxy, -p             Upstream proxy address (direct connection if empty)       (type: string)
    --proxy-timeout, -pt    Upstream proxy timeout                                    (type: string; default: 5s)   
    --certificate, -c       Path to root CA certificate                               (type: string)
    --key, -k               Path to root CA key                                       (type: string)
    --sslkeylog, -s         Path to SSL/TLS secrets log file                          (type: string; default: ssl.log)
    --insecure, -i          Allow connecting to insecure remote hosts                 (type: bool; default: false)
    -h, --help              show help                                                 (type: bool)