sslsniff v0.8 Moxie Marlinspike moxie@thoughtcrime.org

REQUIRES: openssl, libboost1.35-dev, libboost-filesystem1.35-dev, libboost-thread1.35-dev, liblog4cpp5-dev, Linux 2.4/2.6 (or BSD)

The three steps to get this running are:

* Download and run sslsniff-0.8.tar.gz
* Setup iptables (or pf on BSD)
* Run arpspoof (or whatever method you'd like to use to redirect traffic).

Installing sslsniff

* Unpack sslsniff-0.8.tar.gz, run "./configure" and "make". (You'll have
  to make some changes to build on BSD systems, see below under "Setting up 
  pf")
* There are two ways to run this: in "authority" mode or "targeted" mode.

Authority Mode:

In this mode, sslsniff acts as if it is a CA which dynamically generates
certificates on the fly.  If you were, for instance, able to obtain a CA
certificate somehow, you could run it in this mode and it would dynamically
create and sign new certificates for whatever site you're trying to connect
to.

This mode is also useful for exploiting implementations that do not properly
verify BasicConstraints, as any valid leaf node certificate could be used
instead of a CA cert.

You would run sslsniff as: 
./sslsniff -a -s <$listenPort> -w <$logFile> -c <$caCert>

Targeted Mode:

In this mode, sslsniff is given a directory full of certificates, which it 
uses for targeted MITM attacks against the hosts those certificates are 
signed for.  This mode is useful if you are able to forge specific 
certificates, or if you have certificates that were obtained for the "null 
prefix" vulnerability that I published.  There are sample null prefix 
certificates in the "certs" directory that comes with sslsniff, but be
sure to specify "-m IPSCACLASEA1.crt" if you wish to use those. (Note:
the targeted certs have been removed for legal reasons, but the universal
wildcard cert remains)

You would run sslsniff as: 
./sslsniff -t -s <$listenPort> -w <$logFile> -m IPSCACLASEA1.crt \
  -c <$certDir>

Other options:

* sslsniff can be configured to only attack certain clients.  In this case, 
  you need to specify -f <ff,ie,safari,opera> -h <$httpListenPort> 

* sslsniff can be configured to deny OCSP requests from clients.  In this 
  case, you need to specify -d

* sslsniff can be configured to only log HTTP POSTS.  In this case, you 
  need to specify -p

* sslsniff can be configured to hijack Mozilla auto-updates.  In this case, 
  you need to specify -u <$updateXmlDir>, where $updateXmlDir contains the 
  XML files for whatever binaries you want to have sslsniff auto-update, 
  one for each platform.  There are sample XML files in the "update" 
  directory that comes with sslsniff.

* sslsniff can be configured to hijack Firefox/Thunderbird addon 
  auto-updates. In this case, you need to specify -e <url> -j <sha256sum> 
  where <url> is the URL where your custom addon is located, and <sha256sum> 
  is the sha256sum of that addon.

Setting up iptables

* Flip your machine into ip_forward mode 
  (echo 1 > /proc/sys/net/ipv4/ip_forward)

* Add a rule to intercept HTTPS traffic 
  (iptables -t nat -A PREROUTING -p tcp --destination-port 443
   -j REDIRECT --to-ports <$listenPort>)

* If you're going to do client fingerprinting, add a rule to
  intercept HTTP traffic:
  (iptables -t nat -A PREROUTING -p tcp --destination-port 80
  -j REDIRECT --to-ports <$httpListenPort>)

* Add a rule to intercept imaps traffic:
  (iptables -t nat -A PREROUTING -p tcp --destination-port 993 \
   -j REDIRECT --to-ports <$listenPort>)

* Add a rule to intercept pop3s traffic:
  (iptables -t nat -A PREROUTING -p tcp --destination-port 995 \
   -j REDIRECT --to-ports <$listenPort>)

* Add a rule to intercept irc over ssl traffic:
  (iptables -t nat -A PREROUTING -p tcp --destination-port 6697 \
   -j REDIRECT --to-ports <$listenPort>)

Setting up pf

Basic support for pf is now included. Set up firewall rules similar to those above, and change util/Destination.cpp by undefining HAVE_NETFILTER and defining HAVE_PF at the top.

Running arpspoof

Assuming we want to intercept SSL traffic from 172.17.10.36, we need to trick that host into thinking that we're the router. Using arpspoof, we can convince the target that the router's MAC address is our MAC address.

* arpspoof -i eth0 -t 172.17.10.36 172.17.8.1

At this point, any SSL traffic should get proxied by sslsniff and logged to a file.

How does this work?

First, arpspoof convinces a host that our MAC address is the router's MAC address, and the target begins to send us all its network traffic. The kernel forwards everything along except for traffic destined to port 443, which it redirects to $listenPort (10000, for example).

At this point, sslsniff receives the client connection, makes a connection to the real SSL site, and looks at the information in its certificate.
sslsniff then either sends a forged certificate if available (targeted certificate mode), or it dynamically forges a certificate and signs it with your authoritative certificate (authority mode).