SSLSPLIT(1)SSLSPLIT(1)NAMEsslsplit-- transparent and scalable SSL/TLS interception
SYNOPSISsslsplit [-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 inter‐
cepted through a network address translation engine and redirected to
SSLsplit. SSLsplit terminates SSL/TLS and initiates a new SSL/TLS con‐
nection 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 exist‐
ing certificates of which the private key is available, instead of gen‐
erating forged ones. SSLsplit supports NULL-prefix CN certificates and
can deny OCSP requests in a generic way. For HTTP and HTTPS connec‐
tions, SSLsplit removes response headers for HPKP in order to prevent
public key pinning, for HSTS to allow the user to accept untrusted cer‐
tificates, 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 connec‐
tions (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 reca‐
bling, 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 connec‐
tion, a log file will be written, which will contain both direc‐
tions 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 automati‐
cally 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 sup‐
ports 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 connec‐
tion. This makes process information such as pid, owner:group
and executable path for connections originating on the same sys‐
tem 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 open‐
ing 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 reso‐
lution. 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 for‐
mat, including addresses and ports and some HTTP and SSL infor‐
mation, 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 syntacti‐
cally 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 par‐
ticular, 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 uninter‐
rupted 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 proto‐
col 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 dis‐
abling 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 speci‐
fying 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 cer‐
tificate 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 cer‐
tificate 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, lis‐
ten 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 decod‐
ing, 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 redi‐
rect 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 direc‐
tives; 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 omit‐
ted 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 omit‐
ted 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 direc‐
tive 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 direc‐
tive 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 avail‐
able on FreeBSD, NetBSD and Mac OS X. Fully supported, includ‐
ing IPv6. Assuming inbound interface em0, first in old (Free‐
BSD, 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 sup‐
ports IPv4 due to limitations in the SO_ORIGINAL_DST getsock‐
opt(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 dis‐
abling compression and selecting only fast block cipher cipher suites
and using a precomputed private key leaf.key for the forged certifi‐
cates (most significant speed increase is gained by choosing fast algo‐
rithms 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 -usslsplit \
-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 sepa‐
rate disk writer threads to ensure that socket event handling threads
don't have to block on disk I/O. DNS lookups are performed asynchro‐
niously. 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 ALSOopenssl(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 chrono‐
logical 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)
