sslsplit v0.5.4 releases: Transparent SSL/TLS interception

SSLsplit – transparent SSL/TLS interception


SSLsplit is a tool for man-in-the-middle attacks against SSL/TLS encrypted network connections. It is intended to be useful for network forensics, application security analysis, and penetration testing.

SSLsplit is designed to transparently terminate connections that are redirected to it using a network address translation engine. SSLsplit then terminates SSL/TLS and initiates a new SSL/TLS connection to the original destination address, while logging all data transmitted. Besides NAT based operation, SSLsplit also supports static destinations and using the server name indicated by SNI as upstream destination. SSLsplit is purely a transparent proxy and cannot act as a HTTP or SOCKS proxy configured in a browser.

SSLsplit supports plain TCP, plain SSL, HTTP and HTTPS connections over both IPv4 and IPv6. It also has the ability to dynamically upgrade plain TCP to SSL in order to generically support SMTP STARTTLS and similar upgrade mechanisms. 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 built against, SSLsplit supports SSL 3.0, TLS 1.0, TLS 1.1 and TLS 1.2, and optionally SSL 2.0 as well.

For SSL and HTTPS connections, SSLsplit generates and signs forged X509v3 certificates on-the-fly, mimicking the original server certificate’s subject DN, subjectAltName extension and other characteristics. SSLsplit has the ability to use existing certificates of which the private key is available, instead of generating forged ones. SSLsplit supports NULL-prefix CN certificates but otherwise does not implement exploits against specific certificate verification vulnerabilities in SSL/TLS stacks.

SSLsplit implements a number of defences against mechanisms which would normally prevent MitM attacks or make them more difficult. SSLsplit can deny OCSP requests in a generic way. For HTTP and HTTPS connections, SSLsplit mangles headers to prevent server-instructed public key pinning (HPKP), avoid strict transport security restrictions (HSTS), avoid Certificate Transparency enforcement (Expect-CT) and prevent switching to QUIC/SPDY, HTTP/2 or WebSockets (Upgrade, Alternate Protocols). HTTP compression, encodings and keep-alive are disabled to make the logs more readable.

Logging options include traditional SSLsplit connect and content log files as well as PCAP files and mirroring decrypted traffic to a network interface. Additionally, certificates, master secrets and local process information can be logged.

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


SSLsplit 0.5.4 2018-10-29

This release includes work sponsored by HackerOne.

  • Add PCAP content log modes (-X, -Y, -y) and a packet mirroring content log mode (-T, -I) to encapsulate decrypted traffic segments in emulated TCP, IP and Ethernet headers and write the result to PCAP files or send it to a packet capture host on the local network segment (issue #215, based on pull req #149 by @cihankom).
  • Suppress Expect-CT header in order to avoid Certificate Transparency log lookup failures (issue #205).
  • Add -x option for activating an OpenSSL engine (issue #204, pull req #206).
  • Add -f option for loading configuration from file, including a new manual page, sslsplit.conf(5) (pull req #193).
  • Bypass privilege separation overhead for when privileges are not actually dropped; this allows the use of -u root to actively prevent privilege separation and remove the associated IPC overhead (issue #222).
  • Add sudotest target for optional unit tests which require privileges to run successfully.
  • Fix crash when using LibreSSL (pull req #207).
  • Add XNU headers for macOS High Sierra 10.13.1 to 10.13.6.
  • Release sig PGP/GPG key rollover from 0xB5D3397E to 0xE1520675375F5E35.
  • Minor bugfixes and improvements.


git clone
make test # optional unit tests
make sudotest # optional unit tests requiring privileges
make install # optional install


Copyright (c) 2009-2018, Daniel Roethlisberger and contributors.
All rights reserved.