ike-scan

Discover and fingerprint IKE hosts (IPsec VPN Servers)

Table of Contents

• Building and Installing
• Overview
• Usage
• Implementation Details
  • Host Input and Memory Requirements
  • Rate Limiting
  • Cookie Generation and Remote Host Identification
  • IKE Packet Details
  • Backoff Fingerprinting
• Program Output
• Examples
• Supported Platforms
• Further Reading and RFCs
• Contact Information

Building and Installing

ike-scan uses the standard GNU autoconf and automake tools, so installation is the normal process:

• Run git clone https://github.com/royhills/ike-scan.git to obtain the project source code
• Run cd ike-scan to enter source directory
• Run autoreconf --install to generate a viable ./configure file
• Run ./configure or ./configure --with-openssl to use the OpenSSL libraries
• Run make to build the project
• Run make check to verify that everything works as expected
• Run make install to install (you'll need root or sudo for this part)

If you plan on performing pre-shared key cracking, then you should configure ike-scan to use the OpenSSL hash functions rather than its built-in functions because the OpenSSL ones are normally faster. To do this, make sure you have the OpenSSL include files and libraries installed, and run configure as ./configure --with-openssl. Whether you use OpenSSL or not won't affect the functionality of ike-scan, just the speed of pre-shared key cracking with psk-crack.

Some operating systems install the OpenSSL headers and libraries by default; others require that you install an optional package, for example on Debian Linux you need to install the libssl-dev package. Alternatively, you can download and install the OpenSSL tarball from http://www.openssl.org/

It should build on most modern Unix-like OSes. It works on Windows with Cygwin and can be used as a standalone Windows executable when cygwin1.dll is present.

If you are using the Windows-32 binary package, please also read the file README-WIN32 which details the differences when running on the Windows platform.

The program is known to build and run on Linux, FreeBSD, OpenBSD, NetBSD, Win32/Cygwin, Solaris, MacOS X, HP Tru64, HP-UX, and SCO OpenServer. For more details see the section "SUPPORTED PLATFORMS" below.

Overview

ike-scan discovers IKE hosts and can also fingerprint them using the retransmission backoff pattern.

ike-scan can perform the following functions:

• Discovery Determine which hosts in a given IP range are running IKE. This is done by displaying those hosts which respond to the IKE requests sent by ike-scan.
• Fingerprinting Determine which IKE implementation the hosts are using, and in some cases determine the version of software that they are running. This is done in two ways: firstly by UDP backoff fingerprinting which involves recording the times of the IKE response packets from the target hosts and comparing the observed retransmission backoff pattern against known patterns; and secondly by Vendor ID fingerprinting which compares Vendor ID payloads from the VPN servers against known vendor id patterns.
• Transform Enumeration Find which transform attributes are supported by the VPN server for IKE Phase-1 (e.g. encryption algorithm, hash algorithm etc.).
• User Enumeration For some VPN systems, discover valid VPN usernames.
• Pre-Shared Key Cracking Perform offline dictionary or brute-force password cracking for IKE Aggressive Mode with Pre-Shared Key authentication. This uses ike-scan to obtain the hash and other parameters, and psk-crack (which is part of the ike-scan package) to perform the cracking.

The retransmission backoff fingerprinting concept is discussed in more detail in the UDP backoff fingerprinting paper which should be included in the ike-scan kit as UDP Backoff Fingerprinting Paper.

The program sends IKE phase-1 (Main Mode or Aggressive Mode) requests to the specified hosts and displays any responses that are received. It handles retry and retransmission with backoff to cope with packet loss. It also limits the amount of bandwidth used by the outbound IKE packets.

IKE is the Internet Key Exchange protocol which is the key exchange and authentication mechanism used by IPsec. Just about all modern VPN systems implement IPsec, and the vast majority of IPsec VPNs use IKE for key exchange. Main Mode is one of the modes defined for phase-1 of the IKE exchange (the other defined mode is aggressive mode). RFC 2409 section 5 specifies that main mode must be implemented, therefore all IKE implementations can be expected to support main mode. Many also support Aggressive Mode.

Usage

To see current usage information, run the ike-scan binary like so:

ike-scan -h

Additional documentation is provided on the NTA Monitor Wiki

To report bugs or suggest new features, please create a GitHub issue.

Implementation Details

Host Input and Memory Requirements

The hosts to scan can be specified on the command line or read from an input file using the --file=<fn> option. The program can cope with large numbers of hosts limited only by the amount of memory needed to store the list of host_entry structures. Each host_entry structure requires 45 bytes on a 32-bit system, so a class B network (65534 hosts) would require about 2.8 MB for the list. The hosts can be specified as either IP addresses or hostnames, however the program will store all hosts internally as IP addresses and will only display IP addresses in the output (ike-scan calls gethostbyname(3) to determine the IP address of each host, but this can be disabled with the --nodns option).

Rate Limiting

The program limits the rate at which it sends IKE packets to ensure that it does not overload the network connection. By default it uses an outbound data rate of 56000 bits per second. This can be changed with the --bandwidth option.

If you want to send packets at a specific rate, you can use the --interval option.

Cookie Generation and Remote Host Identification

ike-scan generates unique IKE cookies for each host, and it uses these cookies to determine which host the response packets belong to. Note that it does not rely on the source IP address of the response packets because it is possible for a response packet to be sent from a different IP address than it was originally sent to. See the PROGRAM OUTPUT section for an example of this.

The cookies are generated by taking the first 64 bits of an MD5 hash of the current time in seconds and microseconds as returned by gettimeofday(), the unique host number, and the host IP address. This ensures that the cookies are unique with a reasonable degree of certainty.

If --verbose is in effect, any packets that are received with cookies that do not match will result in a message like: