19th November 2014

SSLsplit - transparent and scalable SSL/TLS interception

Copyright 2009–2014 Daniel Roethlisberger and contributors. All rights reserved.
Licensed under a two-clause BSD license.

Latest release: sslsplit-0.4.9.tar.bz2 (.asc)
Documentation: sslsplit(1)READMENEWS
Development: droe/sslsplit — follow @droethlisberger for news


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. 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.


% sslsplit -h
Usage: sslsplit [options...] [proxyspecs...]
  -c pemfile  use CA cert (and key) from pemfile to sign forged certs
  -k pemfile  use CA key (and cert) from pemfile to sign forged certs
  -C pemfile  use CA chain from pemfile (intermediate and root CA certs)
  -K pemfile  use key from pemfile for leaf certs (default: generate)
  -t certdir  use cert+chain+key PEM files from certdir to target all sites
              matching the common names (non-matching: generate if CA)
  -O          deny all OCSP requests on all proxyspecs
  -P          passthrough SSL connections if they cannot be split because of
              client cert auth or no matching cert and no CA (default: drop)
  -g pemfile  use DH group params from pemfile (default: keyfiles or auto)
  -G curve    use ECDH named curve (default: secp160r2 for non-RSA leafkey)
  -Z          disable SSL/TLS compression on all connections
  -s ciphers  use the given OpenSSL cipher suite spec (default: ALL:-aNULL)
  -e engine   specify default NAT engine to use (default: pf)
  -E          list available NAT engines and exit
  -u user     drop privileges to user (default if run as root: nobody)
  -m group    when using -u, override group (default: primary group of user)
  -j jaildir  chroot() to jaildir (impacts -S and sni, see manual page)
  -p pidfile  write pid to pidfile (default: no pid file)
  -l logfile  connect log: log one line summary per connection to logfile
  -L logfile  content log: full data to file or named pipe (excludes -S)
  -S logdir   content log: full data to separate files in dir (excludes -L)
  -d          daemon mode: run in background, log error messages to syslog
  -D          debug mode: run in foreground, log debug messages on stderr
  -V          print version information and exit
  -h          print usage information and exit
  proxyspec = type listenaddr+port [natengine|targetaddr+port|"sni"+port]
  e.g.        http 8080 www.roe.ch 80  # http/4; static hostname dst
              https ::1 8443 2001:db8::1 443   # https/6; static address dst
              https 9443 sni 443     # https/4; SNI DNS lookups
              tcp 10025              # tcp/4; default NAT engine
              ssl 2001:db8::2 9999 pf          # ssl/6; NAT engine 'pf'
  sslsplit -k ca.key -c ca.pem -P  https 8443  https ::1 8443

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


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 engines:

  • 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 (experimental)


SSLsplit is or will be available as a package or port on the following systems:

To install from source:

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.


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


Build Status

Freecode has ceased to exist; I currently announce new releases on my Twitter feed @droethlisberger and by pushing release tags to Github.


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.


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.


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)

Further Reading and Success Stories

These links are provided in the hope that they may be useful, but without implying endorsement of any kind.

SSLsplit was also mentioned in «Bulletproof SSL and TLS» by Ivan Ristić, unfortunately as an alternative to sslstrip, which is not correct. SSLsplit is functionally similar to sslsniff, not sslstrip.

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