ThreatFactor NSIA

h1. ThreatScript Definitions

ThreatScript Definitions are written in ECMAScript (basically the same as JavaScript). The ThreatScript definitions return a Result object which indicates whether a match was observed.

h2. ThreatScript Example

Below is an example of a ThreatScript that triggers if the web-page has a form element.

<pre><code class="javascript">

/*

 * Name: Example.General.Has_Form_Tag

 * Version: 1

 * ID: 1000000

 * Message: Indicates if the page has as a form tag

 * Severity: Low

 */

importPackage(Packages.ThreatScript);

importPackage(Packages.HTTP);

function analyze( httpResponse, variables, environment ){

	var parser = httpResponse.getDocumentParser();

	var location = new URL( httpResponse.getLocation() );

	//Get a list of all script tags

	var tagNameFilter = new TagNameFilter("form");

	var nodesList = parser.extractAllNodesThatMatch(tagNameFilter); 

        if( nodesList.size() > 0 ){

	     return new Result( true, "A form was detected" );

	}

	return new Result( false, "No forms detected" );

}

</code>

</pre>

h2. Analysis Function

ThreatScripts must provide an analyze function that takes 5 arguments:

| *Name*       | *Type*            | *Note*                                                                           |

| httpResponse | HttpResponseData  | See source:trunk/src/net/lukemurphey/nsia/scan/HttpResponseData.java             |

| variables    | Variables         | See source:trunk/src/net/lukemurphey/nsia/scan/scriptenvironment/Variables.java  |

| environment  | Environment       | See source:trunk/src/net/lukemurphey/nsia/scan/ScriptDefinition.java#L605        |

h2. Baseline Function

ThreatScripts may declare a baseline function that will allow the definition to be configured to baseline itself against the previous set of scan results. The baseline function is called by NSIA when a user presses the baseline method for a rule. The objective of the baseline function is to view the provided scan results and ignore the particular finding for the given resource in the future. For example, a definition that triggers when the hash of the web-page changes may define a baseline function that causes it to not trigger unless the web-page hashes changes to yet another value.

Below is an example:

<pre>

<code class="javascript">

function baseline( environment ){

	var previousValue = environment.get("LastObservedHash");

	if( previousValue != null && previousValue.getValue() != null ){

		environment.set("Hash", previousValue.getValue() );

	}

	return true;

}

</code>

</pre>

h2. Meta-Data

ThreatScripts must provide a meta-data that indicates the following information:

| *Name*  | *Valid Input*                                      | *Notes* |

| Name    | <category>.<sub_category>.<definition_name>        |         |

| Version | integer                                            | Should be incremented each time the definition is updated |

| ID      | integer                                            | Must be 1000000 or greater (only official definitions can be less than 1000000)        |

| Message | message to be displayed when definition matches    |         |

| Severity| Either: Low, Medium or High                        |         |

| Invasive| Either: True or False (this argument is optional)  |         |

This meta-data is provided in a comment as name-value pairs (see above ThreatScript example).

h3. Definition Name

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h3. Definition Severity

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h3. Definition References

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h2. Available Packages

A series of packages are available to ThreatScripts in order to perform analysis.

| *Package*            | *Class*            | *Description*                                     |

|/2.HTTP               | URL                | Same as java.net.URL                              |

                       | TagNameFilter      | See http://htmlparser.sourceforge.net/javadoc/org/htmlparser/filters/TagNameFilter.html |

|/2.<default>             | StringUtils        | Provides a trim function for Strings, see source:/trunk/src/net/lukemurphey/nsia/scan/scriptenvironment/StringUtils.java              |

| Debug        | Provides method that allows scripts to create log messages, see source:/trunk/src/net/lukemurphey/nsia/scan/scriptenvironment/Debug.java              |

|/2.ThreatScript       | Result             | Indicates the results of analysis, see source:/trunk/src/net/lukemurphey/nsia/scan/scriptenvironment.Result.java                 |

                       | DataAnalysis       | Provides functions useful for analysis, see source:/trunk/src/net/lukemurphey/nsia/scan/ScriptSignatureUtils.java            |

h2. Debugging ThreatScripts

ThreatScripts can create event log messages by using the sendMessage() function in the Debug class. Simply call _Debug.sendMessage_ with a string as an argument to create an event log message. The event log messages can be viewed in the event log for NSIA.

Generally, script created log messages are used only for debugging and should be disabled on rules you want to use in production.

h2. General Notes When Writing Definitions

h3. ThreatScript Maximum Runtime

ThreatScript  definitions are forceably terminated by the scan engine if the script runs for longer than 10 seconds. Thus, it is important to write definitions that can complete within the timeframe alloted; otherwise, the definition will be flagged as having an error.

h3. Maximum Data Size

The scan engine only provides the first 1 MB of the data observed to the scan engine. Therefore, do not design ThreatScripts that won't work if only the first 1 MB of a larger file is provided.