Provided by: sslsplit_0.5.5-2.1build4_amd64 
NAME
sslsplit -- transparent SSL/TLS interception
SYNOPSIS
sslsplit [-kCKqwWOPZdDgGsrRxeumjplLSFXYyTIMiab] -c pem proxyspecs [...]
sslsplit [-kCKqwWOPZdDgGsrRxeumjplLSFXYyTIMiab] -c pem -t dir proxyspecs [...]
sslsplit [-OPZwWdDgGsrRxeumjplLSFXYyTIMiab] -t dir proxyspecs [...]
sslsplit [-kCKwWOPZdDgGsrRxeumjplLSFXYyTIMi] -f conffile
sslsplit -E
sslsplit -V
sslsplit -h
DESCRIPTION
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. See NAT ENGINES and PROXY SPECIFICATIONS below for specifics on the different modes of
operation.
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,
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.
In order to maximize the chances that a connection can be successfully split, SSLsplit does not verify
upstream server certificates by default. Instead, all certificates including self-signed are accepted
and if the expected hostname signalled in SNI is missing from the server certificate, it will be added to
dynamically forged certificates.
SSLsplit does not automagically redirect any network traffic. 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.
OPTIONS
-a pemfile
Use client certificate from pemfile when destination server requests a client certificate. -A
pemfile Use private key, certificate and certificate chain from PEM file pemfile as leaf
certificate instead of generating a leaf certificate on the fly. The PEM file must contain a
single private key, a single certificate and optionally intermediate and root CA certificates to
use as certificate chain. When using -t, SSLsplit will first attempt to use a matching
certificate loaded from certdir. If -t is also used and a connection matches any certificate in
the directory specified with the -t option, that matching certificate is used instead, taking
precedence over the certificate specified with -A.
-b pemfile
Use client private key from pemfile when destination server requests a client certificate.
-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 conffile
Read configuration from conffile.
-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. Only one of -F, -L and -S may be used (last one wins).
-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 group parameters are
automatically used. 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 (ECDHE) cipher suites. If -G is
not given, a default curve (prime256v1) is used automatically. 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.
-I if Mirror connection content as emulated packets to interface if with destination address given by
-T. This option is not available if SSLsplit was built without mirroring support.
-j jaildir
Change the root directory to jaildir using chroot(2) after opening files. Note that this has
implications for sni proxyspecs. 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 the leaf certificates forged on-the-fly. If -K is not given,
SSLsplit will generate a random 2048 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. SIGUSR1 will cause logfile to be re-opened.
-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. SIGUSR1 will cause logfile to be re-opened. Only one of -F, -L and -S may be
used (last one wins).
-m When dropping privileges using -u, override the target primary group to be set to group.
-M logfile
Log master keys to logfile in SSLKEYLOGFILE format as defined by Mozilla. Logging master keys in
this format allows for decryption of SSL/TLS traffic using Wireshark. Note that unlike browsers
implementing this feature, setting the SSLKEYLOGFILE environment variable has no effect on
SSLsplit. SIGUSR1 will cause logfile to be re-opened.
-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 targeted 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. In these situations, passthrough with -P
results in uninterrupted service for the clients, while dropping is the more secure alternative if
unmonitored connections must be prevented. Passthrough mode currently does not apply to SSL/TLS
errors in the connection from the client, since the connection from the client cannot easily be
retried. Specifically, -P does not currently work for clients that do not accept forged
certificates.
-q crlurl
Set CRL distribution point (CDP) crlurl on forged leaf certificates. Some clients, such as some
.NET applications, reject certificates that do not carry a CDP. When using -q, you will need to
generate an empty CRL signed by the CA certificate and key provided with -c and -k, and make it
available at crlurl.
-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. Only one of -F, -L and -S may be used (last
one wins).
-t certdir
Use private key, certificate and certificate chain from PEM files in certdir for connections to
hostnames matching the respective certificates, 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. When using -t, SSLsplit will
first attempt to use a matching certificate loaded from certdir. If -A is also given, when there
is no match in certdir, the default key, certificate and certificate chain from the PEM file
specified with the -A option is used instead. Otherwise, if -c and -k are also given,
certificates will be forged on-the-fly for sites matching none of the common names in the
certificates loaded from certdir. Otherwise, connections matching no certificate will be dropped,
or if -P is given, passed through without splitting SSL/TLS.
-T addr
Mirror connection content as emulated packets to destination address addr on the interface given
by -I. Only IPv4 target addresses are currently supported. This option is not available if
SSLsplit was built without mirroring support.
-u user
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). User user needs to be allowed to make
outbound TCP connections, and in some configurations, to also perform DNS resolution. Dropping
privileges enables privilege separation, which incurs latency for certain options, such as
separate per-connection log files. By using -u root, SSLsplit can be run as root without dropping
privileges. Due to an Apple bug, -u cannot be used with pf proxyspecs on Mac OS X.
-x engine
Use the OpenSSL engine with identifier engine as a default engine. The engine must be available
within the OpenSSL ecosystem under the specified identifier, that is, they must be loaded from the
global OpenSSL configuration. If engine is an absolute path, it will be interpreted as path to an
engine dynamically linked library and loaded by path, regardless of global OpenSSL configuration.
This option is only available if built against a version of OpenSSL with engine support.
-X pcapfile
Log connection content to pcapfile in PCAP format, with emulated TCP, IP and Ethernet headers.
SIGUSR1 will cause pcapfile to be re-opened. Only one of -X, -Y and -y may be used (last one
wins).
-Y pcapdir
Log connection content to separate PCAP files under pcapdir. For each connection, a separate PCAP
file will be written. Only one of -X, -Y and -y may be used (last one wins).
-y pcapspec
Log connection content to separate PCAP files with the given path specification (see LOG
SPECIFICATIONS below). For each connection, a separate PCAP file will be written. Only one of
-X, -Y and -y may be used (last one wins).
-V Display version and compiled features information and exit.
-w gendir
Write generated keys and certificates to individual files in gendir. For keys, the key identifier
is used as filename, which consists of the SHA-1 hash of the ASN.1 bit string of the public key,
as referenced by the subjectKeyIdentifier extension in certificates. For certificates, the SHA-1
fingerprints of the original and the used (forged) certificate are combined to form the filename.
Note that only newly generated certificates are written to disk.
-W gendir
Same as -w, but also write original certificates and certificates not newly generated, such as
those loaded from -t.
-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]
autossl listenaddr port [nat-engine|fwdaddr port]
https SSL/TLS interception with HTTP protocol decoding, including the removal of HPKP, HSTS, Upgrade and
Alternate Protocol response headers. This mode currently suppresses WebSockets and HTTP/2.
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, Upgrade and Alternate Protocol response headers. This mode currently suppresses WebSockets
and HTTP/2.
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.
autossl
Plain TCP connection until a Client Hello SSL/TLS message appears in the byte stream, then
automatic upgrade to SSL/TLS interception. This is generic, protocol-independent STARTTLS
support, that may erroneously trigger on byte sequences that look like Client Hello messages even
though there was no actual STARTTLS command issued.
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 Client Hello 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 preferable 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 host and port, separated by a comma, IPv6 addresses using underscore instead of
colon.
%D The destination host, IPv6 addresses using underscore instead of colon.
%p The destination port.
%s The source host and port, separated by a comma, IPv6 addresses using underscore instead of colon.
%S The source host, IPv6 addresses using underscore instead of colon.
%q The source 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. Note that SSLsplit needs permission to open /dev/pf for
reading, which by default means that it needs to run under root privileges. 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.
Note that SSLsplit needs permission to open /dev/ipnat for reading, which by default means that it
needs to run under root privileges. 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. Fully supported including IPv6 since Linux
v3.8-rc1; on older kernels 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
# please contribute a tested ip6tables config
Note that SSLsplit is only able to accept incoming connections if it binds to the correct IP
address (e.g. 192.0.2.1) or on all interfaces (0.0.0.0). REDIRECT uses the local interface
address of the incoming interface as target IP address, or 127.0.0.1 for locally generated
packets.
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.
SIGNALS
A running sslsplit accepts SIGINT and SIGTERM for a clean shutdown and SIGUSR1 to re-open the single-file
log files (such as -l, -L and -X). The canonical way to rotate or post-process logs is to rename the
active log file, send SIGUSR1 to the PID in the PID file given by -p, give SSLsplit some time to flush
buffers after closing the old file, and then post-process the renamed log file. Per-connection log files
(such as -S and -F) are not re-opened because their filename is specific to the connection.
EXIT STATUS
The sslsplit process will exit with 0 on regular shutdown (SIGINT, SIGTERM), and 128 + signal number on
controlled shutdown based on receiving a different signal such as SIGHUP. Exit status in the range
1..127 indicates error conditions.
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 -S /tmp \
https ::1 10443 https 127.0.0.1 10443 \
http ::1 10080 http 127.0.0.1 10080
If the Linux netfilter engine is used with the iptables REDIRECT target, it is important to listen to the
correct IP address (e.g. 192.0.2.1) or on all interfaces (0.0.0.0), otherwise SSLsplit is not able to
accept incoming connections.
Intercepting IMAP/IMAPS using the same settings:
sslsplit -k ca.key -c ca.crt -l connect.log -S /tmp \
ssl ::1 10993 ssl 127.0.0.1 10993 \
tcp ::1 10143 tcp 127.0.0.1 10143
A more targeted 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 -S /tmp \
https ::1 10443 www.example.org 443 \
https 127.0.0.1 10443 www.example.org 443
The original example, but using plain ssl and tcp proxyspecs to avoid header modifications, and logging
to a single PCAP file for post-processing with an external tool. To facilitate log rotation via SIGUSR1,
-p is also given, so external log rotation tools or scripts can read the PID from the PID file.
sslsplit -k ca.key -c ca.crt -X log.pcap -p /var/run/sslsplit.pid \
ssl ::1 10443 ssl 127.0.0.1 10443 \
tcp ::1 10080 tcp 127.0.0.1 10080
The original example, but using SSL options optimized for speed by disabling compression and selecting
only fast 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. Note that clients may
not support all algorithms and key sizes. Also, some clients warn their users about cipher suites they
consider weak.
sslsplit -Z -s NULL:RC4:AES128:-DHE -K leaf.key \
-k ca.key -c ca.crt -l connect.log -S /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 -S /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 2048
openssl req -new -nodes -x509 -sha256 -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 signaling, 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 asynchronously. 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.
For high performance and low latency and when running SSLsplit as root or otherwise in a privilege
separation mode, avoid using options which require a privileged operation to be invoked through privilege
separation for each connection. These are currently all per-connection log types: content log to per-
stream file in dir or filespec (-F, -S), content log to per-stream PCAP in dir or filespec (-Y, -y), and
generated or all certificates to files in directory (-w, -W). Instead, use the respective single-file
variants where available. It is possible, albeit not recommended, to bypass the default privilege
separation when run as root by using -u root, thereby bypassing privilege separation entirely.
SEE ALSO
sslsplit.conf(5), 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>. SSLsplit is currently maintained by
Daniel Roethlisberger and Soner Tari.
The following individuals have contributed code or documentation, in chronological order of their first
contribution: Steve Wills, Landon Fuller, Wayne Jensen, Rory McNamara, Alexander Neumann, Adam Jacob
Muller, Richard Poole, Maciej Kotowicz, Eun Soo Park, Christian Groschupp, Alexander Savchenkov, Soner
Tari, Petr Vanek, Hilko Bengen, Philip Duldig, Levente Polyak, Nick French, Cihan Komecoglu and Sergey
Pinaev.
SSLsplit contains work sponsored by HackerOne.
BUGS
Use Github for submission of bug reports or patches:
https://github.com/droe/sslsplit
sslsplit 0.5.5 2024-04-01 sslsplit(1)