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SSLsplit - transparent and scalable SSL/TLS interception

Overview

SSLsplit is a tool for man-in-the-middle attacks against SSL/TLS encrypted network connections. Connections are transparently intercepted through a network address translation engine and redirected to SSLsplit. SSLsplit terminates SSL/TLS and initiates a new SSL/TLS connection to the original destination address, while logging all data transmitted. SSLsplit is intended to be useful for network forensics and penetration testing.

SSLsplit supports plain TCP, plain SSL, HTTP and HTTPS connections over both IPv4 and IPv6. For SSL and HTTPS connections, SSLsplit generates and signs forged X509v3 certificates on-the-fly, based on the original server certificate subject DN and subjectAltName extension. SSLsplit fully supports Server Name Indication (SNI) and is able to work with RSA, DSA and ECDSA keys and DHE and ECDHE cipher suites. Depending on the version of OpenSSL, SSLsplit supports SSL 3.0, TLS 1.0, TLS 1.1 and TLS 1.2, and optionally SSL 2.0 as well. SSLsplit can also use existing certificates of which the private key is available, instead of generating forged ones. SSLsplit supports NULL-prefix CN certificates and can deny OCSP requests in a generic way. For HTTP and HTTPS connections, SSLsplit removes response headers for HPKP in order to prevent public key pinning, for HSTS to allow the user to accept untrusted certificates, and Alternate Protocols to prevent switching to QUIC/SPDY.

See the manual page sslsplit(1) for details on using SSLsplit and setting up the various NAT engines.

Requirements

SSLsplit depends on the OpenSSL and libevent 2.x libraries. The build depends on GNU make and a POSIX.2 environment in PATH. The optional unit tests depend on the check library.

SSLsplit currently supports the following operating systems and NAT mechanisms:

FreeBSD: pf rdr and divert-to, ipfw fwd, ipfilter rdr
OpenBSD: pf rdr-to and divert-to
Linux: netfilter REDIRECT and TPROXY
Mac OS X: ipfw fwd and pf rdr

Installation

make
make test       # optional unit tests
make install    # optional install

Dependencies are autoconfigured using pkg-config. If dependencies are not picked up and fixing PKG_CONFIG_PATH does not help, you can specify their respective locations manually by setting OPENSSL_BASE, LIBEVENT_BASE and/or CHECK_BASE to the respective prefixes.

You can override the default install prefix (/usr/local) by setting PREFIX. For more build options see GNUmakefile.

Development

SSLsplit is being developed on Github. For bug reports, please use the Github issue tracker. For patch submissions, please send me pull requests.

https://github.com/droe/sslsplit

License

SSLsplit is provided under the simplified BSD license. SSLsplit contains components licensed under the MIT and APSL licenses. See the respective source file headers for details.

Credits

SSLsplit was inspired by mitm-ssl by Claes M. Nyberg and sslsniff by Moxie Marlinspike, but shares no source code with them.

SSLsplit includes khash.h by Attractive Chaos.

Contributors

The following individuals have contributed to the SSLsplit codebase, in chronological order of first contribution:

Daniel Roethlisberger (@droe), main author
Steve Wills (@swills)
Landon Fuller (@landonf)