Provided by: sslsplit_0.4.11+dfsg-2_amd64 
NAME
sslsplit -- transparent and scalable SSL/TLS interception
SYNOPSIS
sslsplit [-kCKOPZdDgGsrReumjplLSFi] -c pem proxyspecs [...]
sslsplit [-kCKOPZdDgGsrReumjplLSFi] -c pem -t dir proxyspecs [...]
sslsplit [-OPZdDgGsrReumjplLSFi] -t dir proxyspecs [...]
sslsplit -E
sslsplit -V
sslsplit -h
DESCRIPTION
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.
SSLsplit supports a number of NAT engines, static forwarding and SNI DNS lookups to
determine the original destination of redirected connections (see NAT ENGINES and PROXY
SPECIFICATIONS below).
To actually implement an attack, you also need to redirect the traffic to the system
running sslsplit. Your options include running sslsplit on a legitimate router, ARP
spoofing, ND spoofing, DNS poisoning, deploying a rogue access point (e.g. using hostap
mode), physical recabling, malicious VLAN reconfiguration or route injection, /etc/hosts
modification and so on. SSLsplit does not implement the actual traffic redirection.
OPTIONS
-c pemfile
Use CA certificate from pemfile to sign certificates forged on-the-fly. If pemfile
also contains the matching CA private key, it is also loaded, otherwise it must be
provided with -k. If pemfile also contains Diffie-Hellman group parameters, they
are also loaded, otherwise they can be provided with -g. If -t is also given,
SSLsplit will only forge a certificate if there is no matching certificate in the
provided certificate directory.
-C pemfile
Use CA certificates from pemfile as extra certificates in the certificate chain.
This is needed if the CA given with -k and -c is a sub-CA, in which case any
intermediate CA certificates and the root CA certificate must be included in the
certificate chain.
-d Detach from TTY and run as a daemon, logging error messages to syslog instead of
standard error.
-D Run in debug mode, log lots of debugging information to standard error. This also
forces foreground mode and cannot be used with -d.
-e engine
Use engine as the default NAT engine for proxyspecs without explicit NAT engine,
static destination address or SNI mode. engine can be any of the NAT engines
supported by the system, as returned by -E.
-E List all supported NAT engines available on the system and exit. See NAT ENGINES
for a list of NAT engines currently supported by SSLsplit.
-F logspec
Log connection content to separate log files with the given path specification (see
LOG SPECIFICATIONS below). For each connection, a log file will be written, which
will contain both directions of data as transmitted. Information about the
connection will be contained in the filename only. If -F is used with -j, logspec
is relative to jaildir. If -F is used with -u, logspec must be writable by user.
-g pemfile
Use Diffie-Hellman group parameters from pemfile for Ephemereal Diffie-Hellman
(EDH/DHE) cipher suites. If -g is not given, SSLsplit first tries to load DH
parameters from the PEM files given by -K, -k or -c. If no DH parameters are found
in the key files, built-in 512 or 1024 bit group parameters are automatically used
iff a non-RSA private key is given with -K. This is because DSA/DSS private keys
can by themselves only be used for signing and thus require DH to exchange an
SSL/TLS session key. If -g is given, the parameters from the given pemfile will
always be used, even with RSA private keys (within the cipher suites available in
OpenSSL). The -g option is only available if SSLsplit was built against a version
of OpenSSL which supports Diffie-Hellman cipher suites.
-G curve
Use the named curve for Ephemereal Elliptic Curve Diffie-Hellman (EECDH) cipher
suites. If -G is not given, a default curve (secp160r2) is used automatically iff
a non-RSA private key is given with -K. This is because ECDSA/ECDSS private keys
can by themselves only be used for signing and thus require ECDH to exchange an
SSL/TLS session key. If -G is given, the named curve will always be used, even
with RSA private keys (within the cipher suites available in OpenSSL). The -G
option is only available if SSLsplit was built against a version of OpenSSL which
supports Elliptic Curve Diffie-Hellman cipher suites.
-h Display help on usage and exit.
-i For each connection, find the local process owning the connection. This makes
process information such as pid, owner:group and executable path for connections
originating on the same system as SSLsplit available to the connect log and enables
the respective -F path specification directives. -i is available on Mac OS X and
FreeBSD; support for other platforms has not been implemented yet.
-j jaildir
Change the root directory to jaildir using chroot(2) after opening files. Note
that this has implications for -F, -S, and for sni proxyspecs. The path given with
-S or -F will be relative to jaildir since the log files cannot be opened before
calling chroot(2). Depending on your operating system, you will need to copy files
such as /etc/resolv.conf to jaildir in order for name resolution to work. Using
sni proxyspecs depends on name resolution. Some operating systems require special
device nodes such as /dev/null to be present within the jail. Check your system's
documentation for details.
-k pemfile
Use CA private key from pemfile to sign certificates forged on-the-fly. If pemfile
also contains the matching CA certificate, it is also loaded, otherwise it must be
provided with -c. If pemfile also contains Diffie-Hellman group parameters, they
are also loaded, otherwise they can be provided with -g. If -t is also given,
SSLsplit will only forge a certificate if there is no matching certificate in the
provided certificate directory.
-K pemfile
Use private key from pemfile for certificates forged on-the-fly. If -K is not
given, SSLsplit will generate a random 1024-bit RSA key.
-l logfile
Log connections to logfile in a single line per connection format, including
addresses and ports and some HTTP and SSL information, if available.
-L logfile
Log connection content to logfile. The content log will contain a parsable log
format with transmitted data, prepended with headers identifying the connection and
the data length of each logged segment.
-m When dropping privileges using -u, override the target primary group to be set to
group.
-O Deny all Online Certificate Status Protocol (OCSP) requests on all proxyspecs and
for all OCSP servers with an OCSP response of tryLater, causing OCSP clients to
temporarily accept even revoked certificates. HTTP requests are being treated as
OCSP requests if the method is GET and the URI contains a syntactically valid
OCSPRequest ASN.1 structure parsable by OpenSSL, or if the method is POST and the
Content-Type is application/ocsp-request. For this to be effective, SSLsplit must
be handling traffic destined to the port used by the OCSP server. In particular,
SSLsplit must be configured to receive traffic to all ports used by OCSP servers of
targetted certificates within the certdir specified by -t.
-p pidfile
Write the process ID to pidfile and refuse to run if the pidfile is already in use
by another process.
-P Passthrough SSL/TLS connections which cannot be split instead of dropping them.
Connections cannot be split if -c and -k are not given and the site does not match
any certificate loaded using -t, or if the connection to the original server gives
SSL/TLS errors. Specifically, this happens if the site requests a client
certificate. Passthrough with -P results in uninterrupted service for the clients,
while dropping is the more secure alternative if unmonitored connections must be
prevented.
-r proto
Force SSL/TLS protocol version on both client and server side to proto by selecting
the respective OpenSSL method constructor instead of the default SSLv23_method()
which supports all protocol versions. This is useful when analyzing traffic to a
server that only supports a specific version of SSL/TLS and does not implement
proper protocol negotiation. Depending on build options and the version of OpenSSL
that is used, the following values for proto are accepted: ssl2, ssl3, tls10, tls11
and tls12. Note that SSL 2.0 support is not built in by default because some
servers don't handle SSL 2.0 Client Hello messages gracefully.
-R proto
Disable the SSL/TLS protocol version proto on both client and server side by
disabling the respective protocols in OpenSSL. To disable multiple protocol
versions, -R can be given multiple times. If -r is also given, there will be no
effect in disabling other protocol versions. Disabling protocol versions is useful
when analyzing traffic to a server that does not handle some protocol versions
well, or to test behaviour with different protocol versions. Depending on build
options and the version of OpenSSL that is used, the following values for proto are
accepted: ssl2, ssl3, tls10, tls11 and tls12. Note that SSL 2.0 support is not
built in by default because some servers don't handle SSL 2.0 Client Hello messages
gracefully.
-s ciphers
Use OpenSSL ciphers specification for both server and client SSL/TLS connections.
If -s is not given, a cipher list of ALL:-aNULL is used. Normally, SSL/TLS
implementations choose the most secure cipher suites, not the fastest ones. By
specifying an appropriate OpenSSL cipher list, the set of cipher suites can be
limited to fast algorithms, or eNULL cipher suites can be added. Note that for
connections to be successful, the SSLsplit cipher suites must include at least one
cipher suite supported by both the client and the server of each connection. See
ciphers(1) for details on how to construct OpenSSL cipher lists.
-S logdir
Log connection content to separate log files under logdir. For each connection, a
log file will be written, which will contain both directions of data as
transmitted. Information about the connection will be contained in the filename
only. If -S is used with -j, logdir is relative to jaildir. If -S is used with
-u, logdir must be writable by user.
-t certdir
Use private key, certificate and certificate chain from PEM files in certdir for
sites matching the respective common names, instead of using certificates forged
on-the-fly. A single PEM file must contain a single private key, a single
certificate and optionally intermediate and root CA certificates to use as
certificate chain. If -c and -k are also given, certificates will be forged on-
the-fly for sites matching none of the certificates loaded from certdir.
Otherwise, connections matching no certificate will be dropped, or if -P is given,
passed through without splitting SSL/TLS.
-u Drop privileges after opening sockets and files by setting the real, effective and
stored user IDs to user and loading the appropriate primary and ancillary groups.
If -u is not given, SSLsplit will drop privileges to the stored UID if EUID != UID
(setuid bit scenario), or to nobody if running with full root privileges (EUID ==
UID == 0) and -S is not used. Due to an Apple bug, -u cannot be used with pf
proxyspecs on Mac OS X.
-V Display version and compiled features information and exit.
-Z Disable SSL/TLS compression on all connections. This is useful if your limiting
factor is CPU, not network bandwidth. The -Z option is only available if SSLsplit
was built against a version of OpenSSL which supports disabling compression.
PROXY SPECIFICATIONS
Proxy specifications (proxyspecs) consist of the connection type, listen address and
static forward address or address resolution mechanism (NAT engine, SNI DNS lookup):
https listenaddr port [nat-engine|fwdaddr port|sni port]
ssl listenaddr port [nat-engine|fwdaddr port|sni port]
http listenaddr port [nat-engine|fwdaddr port]
tcp listenaddr port [nat-engine|fwdaddr port]
https SSL/TLS interception with HTTP protocol decoding, including the removal of HPKP,
HSTS and Alternate Protocol response headers.
ssl SSL/TLS interception without any lower level protocol decoding; decrypted
connection content is treated as opaque stream of bytes and not modified.
http Plain TCP connection without SSL/TLS, with HTTP protocol decoding, including the
removal of HPKP, HSTS and Alternate Protocol response headers.
tcp Plain TCP connection without SSL/TLS and without any lower level protocol decoding;
decrypted connection content is treated as opaque stream of bytes and not modified.
listenaddr port
IPv4 or IPv6 address and port or service name to listen on. This is the address
and port where the NAT engine should redirect connections to.
nat-engine
NAT engine to query for determining the original destination address and port of
transparently redirected connections. If no engine is given, the default engine is
used, unless overridden with -e. When using a NAT engine, sslsplit needs to run on
the same system as the NAT rules redirecting the traffic to sslsplit. See NAT
ENGINES for a list of supported NAT engines.
fwdaddr port
Static destination address, IPv4 or IPv6, with port or service name. When this is
used, connections are forwarded to the given server address and port. If fwdaddr
is a hostname, it will be resolved to an IP address.
sni port
Use the Server Name Indication (SNI) hostname sent by the client in the ClientHello
SSL/TLS message to determine the IP address of the server to connect to. This only
works for ssl and https proxyspecs and needs a port or service name as an argument.
Because this requires DNS lookups, it is preferrable to use NAT engine lookups (see
above), except when that is not possible, such as when there is no supported NAT
engine or when running sslsplit on a different system than the NAT rules
redirecting the actual connections. Note that when using -j with sni, you may need
to prepare jaildir to make name resolution work from within the chroot directory.
LOG SPECIFICATIONS
Log specifications are composed of zero or more printf-style directives; ordinary
characters are included directly in the output path. SSLsplit current supports the
following directives:
%T The initial connection time as an ISO 8601 UTC timestamp.
%d The destination address and port.
%s The source address and port.
%x The name of the local process. Requires -i to be used. If process information is
unavailable, this directive will be omitted from the output path.
%X The full path of the local process. Requires -i to be used. If process
information is unavailable, this directive will be omitted from the output path.
%u The username or numeric uid of the local process. Requires -i to be used. If
process information is unavailable, this directive will be omitted from the output
path.
%g The group name or numeric gid of the local process. Requires -i to be used. If
process information is unavailable, this directive will be omitted from the output
path.
%% A literal '%' character.
NAT ENGINES
SSLsplit currently supports the following NAT engines:
pf OpenBSD packet filter (pf) rdr/rdr-to NAT redirects, also available on FreeBSD,
NetBSD and Mac OS X. Fully supported, including IPv6. Assuming inbound interface
em0, first in old (FreeBSD, Mac OS X), then in new (OpenBSD 4.7+) syntax:
rdr pass on em0 proto tcp from 2001:db8::/64 to any port 80 \
-> ::1 port 10080
rdr pass on em0 proto tcp from 2001:db8::/64 to any port 443 \
-> ::1 port 10443
rdr pass on em0 proto tcp from 192.0.2.0/24 to any port 80 \
-> 127.0.0.1 port 10080
rdr pass on em0 proto tcp from 192.0.2.0/24 to any port 443 \
-> 127.0.0.1 port 10443
pass in quick on em0 proto tcp from 2001:db8::/64 to any \
port 80 rdr-to ::1 port 10080
pass in quick on em0 proto tcp from 2001:db8::/64 to any \
port 443 rdr-to ::1 port 10443
pass in quick on em0 proto tcp from 192.0.2.0/24 to any \
port 80 rdr-to 127.0.0.1 port 10080
pass in quick on em0 proto tcp from 192.0.2.0/24 to any \
port 443 rdr-to 127.0.0.1 port 10443
ipfw FreeBSD IP firewall (IPFW) divert sockets, also available on Mac OS X. Available
on FreeBSD and OpenBSD using pf divert-to. Fully supported on FreeBSD and OpenBSD,
including IPv6. Only supports IPv4 on Mac OS X due to the ancient version of IPFW
included. First in IPFW, then in pf divert-to syntax:
ipfw add fwd ::1,10080 tcp from 2001:db8::/64 to any 80
ipfw add fwd ::1,10443 tcp from 2001:db8::/64 to any 443
ipfw add fwd 127.0.0.1,10080 tcp from 192.0.2.0/24 to any 80
ipfw add fwd 127.0.0.1,10443 tcp from 192.0.2.0/24 to any 443
pass in quick on em0 proto tcp from 2001:db8::/64 to any \
port 80 divert-to ::1 port 10080
pass in quick on em0 proto tcp from 2001:db8::/64 to any \
port 443 divert-to ::1 port 10443
pass in quick on em0 proto tcp from 192.0.2.0/24 to any \
port 80 divert-to 127.0.0.1 port 10080
pass in quick on em0 proto tcp from 192.0.2.0/24 to any \
port 443 divert-to 127.0.0.1 port 10443
ipfilter
IPFilter (ipfilter, ipf), available on many systems, including FreeBSD, NetBSD,
Linux and Solaris. Only supports IPv4 due to limitations in the SIOCGNATL ioctl(2)
interface. Assuming inbound interface bge0:
rdr bge0 0.0.0.0/0 port 80 -> 127.0.0.1 port 10080
rdr bge0 0.0.0.0/0 port 443 -> 127.0.0.1 port 10443
netfilter
Linux netfilter using the iptables REDIRECT target. Only supports IPv4 due to
limitations in the SO_ORIGINAL_DST getsockopt(2) interface.
iptables -t nat -A PREROUTING -s 192.0.2.0/24 \
-p tcp --dport 80 \
-j REDIRECT --to-ports 10080
iptables -t nat -A PREROUTING -s 192.0.2.0/24 \
-p tcp --dport 443 \
-j REDIRECT --to-ports 10443
tproxy Linux netfilter using the iptables TPROXY target together with routing table magic
to allow non-local traffic to originate on local sockets. Fully supported,
including IPv6.
ip -f inet6 rule add fwmark 1 lookup 100
ip -f inet6 route add local default dev lo table 100
ip6tables -t mangle -N DIVERT
ip6tables -t mangle -A DIVERT -j MARK --set-mark 1
ip6tables -t mangle -A DIVERT -j ACCEPT
ip6tables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT
ip6tables -t mangle -A PREROUTING -s 2001:db8::/64 \
-p tcp --dport 80 \
-j TPROXY --tproxy-mark 0x1/0x1 --on-port 10080
ip6tables -t mangle -A PREROUTING -s 2001:db8::/64 \
-p tcp --dport 443 \
-j TPROXY --tproxy-mark 0x1/0x1 --on-port 10443
ip -f inet rule add fwmark 1 lookup 100
ip -f inet route add local default dev lo table 100
iptables -t mangle -N DIVERT
iptables -t mangle -A DIVERT -j MARK --set-mark 1
iptables -t mangle -A DIVERT -j ACCEPT
iptables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT
iptables -t mangle -A PREROUTING -s 192.0.2.0/24 \
-p tcp --dport 80 \
-j TPROXY --tproxy-mark 0x1/0x1 --on-port 10080
iptables -t mangle -A PREROUTING -s 192.0.2.0/24 \
-p tcp --dport 443 \
-j TPROXY --tproxy-mark 0x1/0x1 --on-port 10443
Note that return path filtering (rp_filter) also needs to be disabled on interfaces
which handle TPROXY redirected traffic.
EXAMPLES
Matching the above NAT engine configuration samples, intercept HTTP and HTTPS over IPv4
and IPv6 using forged certificates with CA private key ca.key and certificate ca.crt,
logging connections to connect.log and connection data into separate files under /tmp (add
-e nat-engine to select the appropriate engine if multiple engines are available on your
system):
sslsplit -k ca.key -c ca.crt -l connect.log -L /tmp \
https ::1 10443 https 127.0.0.1 10443 \
http ::1 10080 http 127.0.0.1 10080
Intercepting IMAP/IMAPS using the same settings:
sslsplit -k ca.key -c ca.crt -l connect.log -L /tmp \
ssl ::1 10993 ssl 127.0.0.1 10993 \
tcp ::1 10143 tcp 127.0.0.1 10143
A more targetted setup, HTTPS only, using certificate/chain/key files from /path/to/cert.d
and statically redirecting to www.example.org instead of querying a NAT engine:
sslsplit -t /path/to/cert.d -l connect.log -L /tmp \
https ::1 10443 www.example.org 443 \
https 127.0.0.1 10443 www.example.org 443
The original example, but using SSL options optimized for speed by disabling compression
and selecting only fast block cipher cipher suites and using a precomputed private key
leaf.key for the forged certificates (most significant speed increase is gained by
choosing fast algorithms and small keysizes for the CA and leaf private keys; check
openssl speed for algorithm performance on your system):
sslsplit -Z -s NULL:RC4:AES128 -K leaf.key \
-k ca.key -c ca.crt -l connect.log -L /tmp \
https ::1 10443 https 127.0.0.1 10443 \
http ::1 10080 http 127.0.0.1 10080
The original example, but running as a daemon under user sslsplit and writing a PID file:
sslsplit -d -p /var/run/sslsplit.pid -u sslsplit \
-k ca.key -c ca.crt -l connect.log -L /tmp \
https ::1 10443 https 127.0.0.1 10443 \
http ::1 10080 http 127.0.0.1 10080
To generate a CA private key ca.key and certificate ca.crt using OpenSSL:
cat >x509v3ca.cnf <<'EOF'
[ req ]
distinguished_name = reqdn
[ reqdn ]
[ v3_ca ]
basicConstraints = CA:TRUE
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer:always
EOF
openssl genrsa -out ca.key 1024
openssl req -new -nodes -x509 -sha1 -out ca.crt -key ca.key \
-config x509v3ca.cnf -extensions v3_ca \
-subj '/O=SSLsplit Root CA/CN=SSLsplit Root CA/' \
-set_serial 0 -days 3650
NOTES
SSLsplit is able to handle a relatively high number of listeners and connections due to a
multithreaded, event based architecture based on libevent, taking advantage of platform
specific select() replacements such as kqueue. The main thread handles the listeners and
signalling, while a number of worker threads equal to twice the number of CPU cores is
used for handling the actual connections in separate event bases, including the CPU-
intensive SSL/TLS handling.
Care has been taken to choose well-performing data structures for caching certificates and
SSL sessions. Logging is implemented in separate disk writer threads to ensure that
socket event handling threads don't have to block on disk I/O. DNS lookups are performed
asynchroniously. SSLsplit uses SSL session caching on both ends to minimize the amount of
full SSL handshakes, but even then, the limiting factor in handling SSL connections are
the actual bignum computations.
SEE ALSO
openssl(1), ciphers(1), speed(1), pf(4), ipfw(8), iptables(8), ip6tables(8), ip(8),
hostapd(8), arpspoof(8), parasite6(8), yersinia(8), https://www.roe.ch/SSLsplit
AUTHORS
SSLsplit was written by Daniel Roethlisberger <daniel@roe.ch>.
The following individuals have contributed to the codebase, in chronological order of
their first contribution: Steve Wills, Landon Fuller and Wayne Jensen.
BUGS
Use Github for submission of bug reports or patches:
https://github.com/droe/sslsplit
1 April 2012 SSLSPLIT(1)