TCP/IP stack fingerprinting is the remote detection of the characteristics of a TCP/IP stack implementation. The combination of parameters may then be used to infer the remote machine's operating system (aka, OS fingerprinting), or incorporated into a device fingerprint.
Certain parameters within the TCP protocol definition are left up to the implementation. Different operating systems, and different versions of the same operating system, set different defaults for these values. By collecting and examining these values, one may differentiate among various operating systems and implementations of TCP/IP. The TCP/IP fields that may vary include the following:
These values may be combined to form a 67-bit signature, or fingerprint, for the target machine. [1] Just inspecting the Initial TTL and window size fields is often enough to successfully identify an operating system, which eases the task of performing manual OS fingerprinting. [2]
Protection against the fingerprint doorway to attack is achieved by limiting the type and amount of traffic a defensive system responds to. Examples include blocking address masks and timestamps from outgoing ICMP control-message traffic, and blocking ICMP echo replies. A security tool can alert to potential fingerprinting: it can match another machine as having a fingerprinter configuration by detecting its fingerprint. [3]
Disallowing TCP/IP fingerprinting provides protection from vulnerability scanners looking to target machines running a certain operating system. Fingerprinting facilitates attacks. Blocking those ICMP messages is only one of an array of defenses required for full protection against attacks. [4]
Targeting the ICMP datagram, an obfuscator running on top of IP in the internet layer acts as a "scrubbing tool" to confuse the TCP/IP fingerprinting data. These exist for Microsoft Windows, [5] Linux [6] and FreeBSD. [7]
A list of TCP/OS Fingerprinting Tools
The Internet Control Message Protocol (ICMP) is a supporting protocol in the Internet protocol suite. It is used by network devices, including routers, to send error messages and operational information indicating success or failure when communicating with another IP address, for example, an error is indicated when a requested service is not available or that a host or router could not be reached. ICMP differs from transport protocols such as TCP and UDP in that it is not typically used to exchange data between systems, nor is it regularly employed by end-user network applications.
ping is a computer network administration software utility used to test the reachability of a host on an Internet Protocol (IP) network. It is available for virtually all operating systems that have networking capability, including most embedded network administration software.
The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly referred to as TCP/IP. TCP provides reliable, ordered, and error-checked delivery of a stream of octets (bytes) between applications running on hosts communicating via an IP network. Major internet applications such as the World Wide Web, email, remote administration, and file transfer rely on TCP, which is part of the Transport Layer of the TCP/IP suite. SSL/TLS often runs on top of TCP.
In computing, traceroute and tracert are computer network diagnostic commands for displaying possible routes (paths) and measuring transit delays of packets across an Internet Protocol (IP) network. The history of the route is recorded as the round-trip times of the packets received from each successive host in the route (path); the sum of the mean times in each hop is a measure of the total time spent to establish the connection. Traceroute proceeds unless all sent packets are lost more than twice; then the connection is lost and the route cannot be evaluated. Ping, on the other hand, only computes the final round-trip times from the destination point.
The Address Resolution Protocol (ARP) is a communication protocol used for discovering the link layer address, such as a MAC address, associated with a given internet layer address, typically an IPv4 address. This mapping is a critical function in the Internet protocol suite. ARP was defined in 1982 by RFC 826, which is Internet Standard STD 37.
Network utilities are software utilities designed to analyze and configure various aspects of computer networks. The majority of them originated on Unix systems, but several later ports to other operating systems exist.
Explicit Congestion Notification (ECN) is an extension to the Internet Protocol and to the Transmission Control Protocol and is defined in RFC 3168 (2001). ECN allows end-to-end notification of network congestion without dropping packets. ECN is an optional feature that may be used between two ECN-enabled endpoints when the underlying network infrastructure also supports it.
A port scanner is an application designed to probe a server or host for open ports. Such an application may be used by administrators to verify security policies of their networks and by attackers to identify network services running on a host and exploit vulnerabilities.
In information technology, a Christmas tree packet is a packet with every single option set for whatever protocol is in use.
Ettercap is a free and open source network security tool for man-in-the-middle attacks on a LAN. It can be used for computer network protocol analysis and security auditing. It runs on various Unix-like operating systems including Linux, Mac OS X, BSD and Solaris, and on Microsoft Windows. It is capable of intercepting traffic on a network segment, capturing passwords, and conducting active eavesdropping against a number of common protocols. Its original developers later founded Hacking Team.
A ping of death is a type of attack on a computer system that involves sending a malformed or otherwise malicious ping to a computer.
lwIP is a widely used open-source TCP/IP stack designed for embedded systems. lwIP was originally developed by Adam Dunkels at the Swedish Institute of Computer Science and is now developed and maintained by a worldwide network of developers.
Cisco NAC Appliance, formerly Cisco Clean Access (CCA), was a network admission control (NAC) system developed by Cisco Systems designed to produce a secure and clean computer network environment. Originally developed by Perfigo and marketed under the name of Perfigo SmartEnforcer, this network admission control device analyzes systems attempting to access the network and prevents vulnerable computers from joining the network. The system usually installs an application known as the Clean Access Agent on computers that will be connected to the network. This application, in conjunction with both a Clean Access server and a Clean Access Manager, has become common in many universities and corporate environments today. It is capable of managing wired or wireless networks in an in-band or out-of-band configuration mode, and Virtual Private networks (VPN) in an in-band only configuration mode.
A network socket is a software structure within a network node of a computer network that serves as an endpoint for sending and receiving data across the network. The structure and properties of a socket are defined by an application programming interface (API) for the networking architecture. Sockets are created only during the lifetime of a process of an application running in the node.
An idle scan is a TCP port scan method for determining what services are open on a target computer without leaving traces pointing back at oneself. This is accomplished by using packet spoofing to impersonate another computer so that the target believes it's being accessed by the zombie. The target will respond in different ways depending on whether the port is open, which can in turn be detected by querying the zombie.
The uIP is an open-source implementation of the TCP/IP network protocol stack intended for use with tiny 8- and 16-bit microcontrollers. It was initially developed by Adam Dunkels of the Networked Embedded Systems group at the Swedish Institute of Computer Science, licensed under a BSD style license, and further developed by a wide group of developers.
p0f is a passive TCP/IP stack fingerprinting tool. p0f can attempt to identify the system running on machines that send network traffic to the box it is running on, or to a machine that shares a medium with the machine it is running on. p0f can also assist in analysing other aspects of the remote system.
NicheStack is a closed source IPv4 network layer and application implementation for operating systems, written in ANSI "C" and is one of three available from InterNiche Technologies, Inc., designed for use in embedded systems. Its transport layer implementation has historical roots in BSD and the IP layer was derived from a Carnegie Mellon University (CMU) implementation.
The Stream Control Transmission Protocol (SCTP) is a computer networking communications protocol in the transport layer of the Internet protocol suite. Originally intended for Signaling System 7 (SS7) message transport in telecommunication, the protocol provides the message-oriented feature of the User Datagram Protocol (UDP), while ensuring reliable, in-sequence transport of messages with congestion control like the Transmission Control Protocol (TCP). Unlike UDP and TCP, the protocol supports multihoming and redundant paths to increase resilience and reliability.
SoftEther VPN is free open-source, cross-platform, multi-protocol VPN client and VPN server software, developed as part of Daiyuu Nobori's master's thesis research at the University of Tsukuba. VPN protocols such as SSL VPN, L2TP/IPsec, OpenVPN, and Microsoft Secure Socket Tunneling Protocol are provided in a single VPN server. It was released using the GPLv2 license on January 4, 2014. The license was switched to Apache License 2.0 on January 21, 2019.