We're very impressed by the collective smarts of the security community and we highly recommend reading the whole list and investigating any tools you are unfamiliar with. Click any tool name for more details on that particular application, including the chance to read (and write) reviews. Many site elements are explained by tool tips if you hover your mouse over them. Enjoy!
Wireshark (known as Ethereal until a trademark dispute in Summer 2006) is a fantastic open source multi-platform network protocol analyzer. It allows you to examine data from a live network or from a capture file on disk. You can interactively browse the capture data, delving down into just the level of packet detail you need. Wireshark has several powerful features, including a rich display filter language and the ability to view the reconstructed stream of a TCP session. It also supports hundreds of protocols and media types. A tcpdump-like console version named tshark is included. One word of caution is that Wireshark has suffered from dozens of remotely exploitable security holes, so stay up-to-date and be wary of running it on untrusted or hostile networks (such as security conferences).
Read 38 reviews.
Latest release: version 1.10.7 on April 22, 2014 (1 year, 3 months ago).
Metasploit took the security world by storm when it was released in 2004. It is an advanced open-source platform for developing, testing, and using exploit code. The extensible model through which payloads, encoders, no-op generators, and exploits can be integrated has made it possible to use the Metasploit Framework as an outlet for cutting-edge exploitation research. It ships with hundreds of exploits, as you can see in their list of modules. This makes writing your own exploits easier, and it certainly beats scouring the darkest corners of the Internet for illicit shellcode of dubious quality. One free extra is Metasploitable, an intentionally insecure Linux virtual machine you can use for testing Metasploit and other exploitation tools without hitting live servers.
Metasploit was completely free, but the project was acquired by Rapid7 in 2009 and it soon sprouted commercial variants. The Framework itself is still free and open source, but they now also offer a free-but-limited Community edition, a more advanced Express edition ($3,000 per year per user), and a full-featured Pro edition ($15,000 per user per year). Other paid exploitation tools to consider are Core Impact (more expensive) and Canvas (less).
Nessus is one of the most popular and capable vulnerability scanners, particularly for UNIX systems. It was initially free and open source, but they closed the source code in 2005 and removed the free "Registered Feed" version in 2008. It now costs $2,190 per year, which still beats many of its competitors. A free “Nessus Home” version is also available, though it is limited and only licensed for home network use.
Nessus is constantly updated, with more than 70,000 plugins. Key features include remote and local (authenticated) security checks, a client/server architecture with a web-based interface, and an embedded scripting language for writing your own plugins or understanding the existing ones.
Read 11 reviews.
Latest release: version 6.3 on March 3, 2015 (5 months ago).
UNIX users often smugly assert that the best free security tools support their platform first, and Windows ports are often an afterthought. They are usually right, but Cain & Abel is a glaring exception. This Windows-only password recovery tool handles an enormous variety of tasks. It can recover passwords by sniffing the network, cracking encrypted passwords using dictionary, brute-force and cryptanalysis attacks, recording VoIP conversations, decoding scrambled passwords, revealing password boxes, uncovering cached passwords and analyzing routing protocols. It is also well documented.
Read 13 reviews.
Latest release: version 4.9.56 on April 7, 2014 (1 year, 3 months ago).
This excellent bootable live CD Linux distribution comes from the merger of Whax and Auditor. It boasts a huge variety of Security and Forensics tools and provides a rich development environment. User modularity is emphasized so the distribution can be easily customized by the user to include personal scripts, additional tools, customized kernels, etc. BackTrack is succeeded by Kali Linux.
Read 20 reviews.
Latest release: version 5 R3 on Aug. 13, 2012 (2 years, 11 months ago).
Burp Suite is an integrated platform for attacking web applications. It contains a variety of tools with numerous interfaces between them designed to facilitate and speed up the process of attacking an application. All of the tools share the same framework for handling and displaying HTTP messages, persistence, authentication, proxies, logging, alerting and extensibility. There is a limited free version and also Burp Suite Professional ($299 per user per year).
Read 16 reviews.
Latest release: version 1.4.01 on June 3, 2011 (4 years, 2 months ago).
Ettercap is a suite for man in the middle attacks on LAN. It features sniffing of live connections, content filtering on the fly and many other interesting tricks.
It supports active and passive dissection of many protocols (even ciphered ones) and includes many feature for network and host analysis.
Read 8 reviews.
Latest release: version 0.8.0-Lacassagne on Sept. 21, 2013 (1 year, 10 months ago).
Sysinternals provides many small windows utilities that are quite useful for low-level windows hacking. Some are free of cost and/or include source code, while others are proprietary. Survey respondents were most enamored with:
ProcessExplorer for keeping an eye on the files and directories open by any process (like lsof on UNIX).
PsTools for managing (executing, suspending, killing, detailing) local and remote processes.
Autoruns for discovering what executables are set to run during system boot up or login.
RootkitRevealer for detecting registry and file system API discrepancies that may indicate the presence of a user-mode or kernel-mode rootkit.
TCPView, for viewing TCP and UDP traffic endpoints used by each process (like Netstat on UNIX).
Many of the Sysinternals tools originally came with source code and there were even Linux versions. Microsoft acquired Sysinternals in July 2006, promising that “Customers will be able to continue building on Sysinternals' advanced utilities, technical information and source code”. Less than four months later, Microsoft removed most of that source code.
Read 2 reviews.
Latest release: Feb. 4, 2011 (4 years, 6 months ago).
OpenVAS is a vulnerability scanner that was forked from the last free version of Nessus after that tool went proprietary in 2005. OpenVAS plugins are still written in the Nessus NASL language. The project seemed dead for a while, but development has restarted.
Read 28 reviews.
Latest release: version 7.0 on April 25, 2014 (1 year, 3 months ago).
A Java-based web proxy for assessing web application vulnerability. It supports editing/viewing HTTP/HTTPS messages on-the-fly to change items such as cookies and form fields. It includes a web traffic recorder, web spider, hash calculator, and a scanner for testing common web application attacks such as SQL injection and cross-site scripting.
Read 6 reviews.
Latest release: version 3.2.13 on Aug. 8, 2006 (8 years, 12 months ago).
Netstumbler is the best known Windows tool for finding open wireless access points ("wardriving"). They also distribute a WinCE version for PDAs and such named MiniStumbler. The tool is currently free but Windows-only and no source code is provided. It uses a more active approach to finding WAPs than passive sniffers such as Kismet or KisMAC.
Read 5 reviews.
Latest release: version 0.4.0 on April 1, 2004 (11 years, 4 months ago).
While it is far more than a security tool, Google's massive database is a gold mine for security researchers and penetration testers. You can use it to dig up information about a target company by using directives such as “site:target-domain.com” and find employee names, sensitive information that they wrongly thought was hidden, vulnerable software installations, and more. Similarly, when a bug is found in yet another popular webapp, Google can often provide a list of vulnerable servers worldwide within seconds. Check out the Google Hacking Database and Johnny Long's excellent book: Google Hacking for Penetration Testers.
Read 3 reviews.
In its simplest form, WebScarab records the conversations (requests and responses) that it observes, and allows the operator to review them in various ways. WebScarab is designed to be a tool for anyone who needs to expose the workings of an HTTP(S) based application, whether to allow the developer to debug otherwise difficult problems, or to allow a security specialist to identify vulnerabilities in the way that the application has been designed or implemented.
Read 3 reviews.
Latest release: version 20100820-1632 on Aug. 20, 2010 (4 years, 11 months ago).
Core Impact isn't cheap (be prepared to spend at least $30,000), but it is widely considered to be the most powerful exploitation tool available. It sports a large, regularly updated database of professional exploits, and can do neat tricks like exploiting one machine and then establishing an encrypted tunnel through that machine to reach and exploit other boxes. Other good options include Metasploit and Canvas.
Read 9 reviews.
Latest release: version 12 on Aug. 8, 2011 (3 years, 12 months ago).
TrueCrypt is an excellent open source disk encryption system for Windows, Mac, and Linux systems. Users can encrypt entire filesystems, which are then on-the-fly encrypted/decrypted as needed without user intervention beyond initially entering their passphrase. A clever hidden volume feature allows you to hide a second layer of particularly sensitive content with plausible deniability about whether it even exists. Then if you are forced to give up your passphrase, you give them the first-level secret. That only allows them access to the innocuous material you have there, without proving that a second level key even exists.
Read 5 reviews.
Latest release: version 7.1a on Feb. 7, 2012 (3 years, 5 months ago).
Disassembly is a big part of security research. It will help you dissect that Microsoft patch to discover the silently fixed bugs they don't tell you about, or more closely examine a server binary to determine why your exploit isn't working. Many debuggers are available, but IDA Pro has become the de-facto standard for the analysis of hostile code and vulnerability research. This interactive, programmable, extensible, multi-processor disassembler has a graphical interface on Windows and console interfaces on Linux and Mac OS X.
Read 1 review.
Latest release: version 6.5.131217 on Dec. 17, 2013 (1 year, 7 months ago).
Maltego is a forensics and data mining application. It is capable of querying various public data sources and graphically depicting the relationships between entities such as people, companies, web sites, and documents. Maltego is an open source intelligence too, but isn't open source software.
Read 2 reviews.
Latest release: version 3.0.3 on Jan. 17, 2011 (4 years, 6 months ago).
Ophcrack is a free rainbow-table based cracker for Windows passwords (though the tool itself runs on Linux, Windows, and Mac). Features include LM and NTLM hash cracking, a GUI, the ability to load hashes from encrypted SAM recovered from a Windows partition, and a Live CD version. Some tables are provided as a free download but larger ones have to be bought from Objectif Sécurité.
Read 8 reviews.
Latest release: version 3.6.0 on June 4, 2013 (2 years, 1 month ago).
Rapid7 Nexpose is a vulnerability scanner which aims to support the entire vulnerability management lifecycle, including discovery, detection, verification, risk classification, impact analysis, reporting and mitigation. It integrates with Rapid7's Metasploit for vulnerability exploitation. It is sold as standalone software, an appliance, virtual machine, or as a managed service or private cloud deployment. User interaction is through a web browser. There is a free but limited community edition as well as commercial versions which start at $2,000 per user per year.
Read 9 reviews.
PGP is the famous encryption system originally written by Phil Zimmerman which helps secure your data from eavesdroppers and other risks. GnuPG is a very well-regarded open source implementation of the PGP standard (the actual executable is named gpg). While the excellent GnuPG is always free, PGP is now owned by Symantec and costs a lot of money.
Read 1 review.
skipfish is an active web application security reconnaissance tool. It prepares an interactive sitemap for the targeted site by carrying out a recursive crawl and dictionary-based probes. The resulting map is then annotated with the output from a number of active (but hopefully non-disruptive) security checks. The final report generated by the tool is meant to serve as a foundation for professional web application security assessments.
Read 3 reviews.
Latest release: version 2.10b on Dec. 4, 2012 (2 years, 8 months ago).
GFI LanGuard is a network security and vulnerability scanner designed to help with patch management, network and software audits, and vulnerability assessments. The price is based on the number of IP addresses you wish to scan. A free trial version (up to 5 IP addresses) is available.
Read 7 reviews.
Latest release: version 2011 on May 19, 2001 (14 years, 2 months ago).
Acunetix WVS (web vulnerability scanner) automatically checks web applications for vulnerabilities such as SQL Injections, cross site scripting, arbitrary file creation/deletion, and weak password strength on authentication pages. It boasts a comfortable GUI, an ability to create professional security audit and compliance reports, and tools for advanced manual webapp testing.
Read 6 reviews.
Latest release: version 10 on June 24, 2015 (1 month, 1 week ago).
QualysGuard is a popular SaaS (software as a service) vulnerability management offering. It's web-based UI offers network discovery and mapping, asset prioritization, vulnerability assessment reporting and remediation tracking according to business risk. Internal scans are handled by Qualys appliances which communicate back to the cloud-based system.
Read 3 reviews.
Latest release: version 6.18 on Feb. 25, 2011 (4 years, 5 months ago).