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Recog: A Recognition Framework

Recog is a framework for identifying products, services, operating systems, and hardware by matching fingerprints against data returned from various network probes. Recog makes it simple to extract useful information from web server banners, snmp system description fields, and a whole lot more. Recog is open source, please see the LICENSE file for more information.

Gem Version Build Status


Recog consists of both XML fingerprint files and an assortment of code, mostly in Ruby, that makes it easy to develop, test, and use the contained fingerprints. In order to use the included ruby code, a recent version of Ruby (2.1+) is required, along with Rubygems and the bundler gem. Once these dependencies are in place, use the following commands to grab the latest source code and install any additional dependencies.

$ git clone
$ cd recog
$ bundle install


Please note that while the XML fingerprints themselves are quite stable and well-tested, the Ruby codebase in Recog is still fairly new and subject to change quickly. Please contact us (research[at] before leveraging the Recog code within any production projects.


The fingerprints within Recog are stored in XML files, each of which is designed to match a specific protocol response string or field. For example, the file ssh_banners.xml can determine the os, vendor, and sometimes hardware product by matching the initial SSH daemon banner string.

A fingerprint file consists of an XML document like the following:

<fingerprints matches="ssh.banner">
  <fingerprint pattern="^RomSShell_([\d\.]+)$">
    <description>Allegro RomSShell SSH</description>
    <example service.version="4.62">RomSShell_4.62</example>
    <param pos="0" name="service.vendor" value="Allegro"/>
    <param pos="0" name="service.product" value="RomSShell"/>
    <param pos="1" name="service.version"/>

The first line should always consist of the XML version declaration. The first element should always be a fingerpints block with a matches attribute indicating what data this fingerprint file is supposed to match. The matches attribute is normally in the form of protocol.field.

Inside of the fingerprints element there should be one or more fingerprint elements. Every fingerprint must contain a pattern attribute, which contains the regular expression to be used to match against the data. An optional flags attribute can be specified to control how the regular expression is to be interpreted. See the Recog documentation for FLAG_MAP for more information.

Inside of the fingerprint, a description element should contain a human-readable string describing this fingerprint.

At least one example element should be present, however multiple example elements are preferred. These elements are used as part of the test coverage present in rspec which validates that the provided data matches the specified regular expression. Additionally, if the fingerprint is using the param elements to extract field values from the data (described next), you can add these expected extractions as attributes for the example elements. In the example above, this:

<example service.version="4.62">RomSShell_4.62</example>

tests that RomSShell_4.62 matches the provided regular expression and that the value of service.version is 4.62.

The param elements contain a pos attribute, which indicates what capture field from the pattern should be extracted, or 0 for a static string. The name attribute is the key that will be reported in the case of a successful match and the value will either be a static string for pos values of 0 or missing and taken from the captured field.

The example string can be base64 encoded to permit the use of unprintable characters. To signal this to Recog an _encoding attribute with the value of base64 is added to the example element. Based64 encoded text that is longer than 80 characters may be wrapped with newlines as shown below to aid in readability.

<example _encoding="base64">


Once a fingerprint has been added, the example entries can be tested by executing bin/recog_verify against the fingerprint file:

    $ bin/recog_verify xml/ssh_banners.xml

Matches can be tested on the command-line in a similar fashion:

    $ echo 'OpenSSH_6.6p1 Ubuntu-2ubuntu1' | bin/recog_match xml/ssh_banners.xml -
    MATCH: {"matched"=>"OpenSSH running on Ubuntu 14.04", "service.version"=>"6.6p1", "openssh.comment"=>"Ubuntu-2ubuntu1", "service.vendor"=>"OpenBSD", ""=>"OpenSSH", "service.product"=>"OpenSSH", "os.vendor"=>"Ubuntu", "os.device"=>"General", ""=>"Linux", "os.product"=>"Linux", "os.version"=>"14.04", "service.protocol"=>"ssh", "fingerprint_db"=>"ssh.banner", "data"=>"OpenSSH_6.6p1 Ubuntu-2ubuntu1"}

Best Practices

  • Create a single fingerprint for each product as long as the pattern remains clear and readable. If that is not possible, the pattern should be logically decomposed into additional fingerprints.
  • Create regular expressions that allow for flexible version number matching. This ensures greater probability of matching a product. For example, all known public releases of a product report either major.minor or format version numbers. If the fingerprint strictly matches this version number format, it would fail to match a modified build of the product that reports only a major version number format.
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