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The Generate Phase

Scope of the phase

This phase is used in a modifying extension and is optional for its operation (the generate section may be either absent or present in the YAML file).

This phase should be absent from the non-modifying extension's YAML file.

Read about the extension types in detail here.

Request element description syntax

When creating a FAST extension, you need to understand the structure of the HTTP request sent to the application and that of the HTTP response received from the application in order to correctly describe the request elements that you need to work with using the points.

To see detailed information, proceed to this link.

This phase specifies a payload to be inserted in the particular parameters of a baseline request to create a test requests that are based on this request.

The generate section has the following structure:

  - into:
    - parameter 1
    - parameter 2
    - …
    - parameter N
  - method:
    - postfix
    - prefix
    - random
    - replace
  - payload:
    - payload 1
    - payload 2
    - …
    - payload N
  • The into parameter allows the specification of single or multiple request elements that the payload should be inserted into. This parameter's value can be a string or an array of strings. You can use a Ruby-formatted regular expression as the into parameter's value.

    This parameter is optional and it may be absent in the section. If the into parameter is omitted, the payload is inserted into the request element that is allowed to be modified according to the given test policy.

    Let us suppose that the following mutable request elements were extracted from the baseline request according to the test policy:

    • GET_uid_value
    • HEADER_COOKIE_value

    The extension will sequentially process all of the mutable elements (also known as insertion points).

    If the into parameter is absent, then the payloads will be sequentially pasted into the GET_uid_value parameter and the produced test requests will be used to check the target application for vulnerabilities. Then, after the test request results are processed, the extension processes the HEADER_COOKIE_value parameter and similarly inserts the payloads into this parameter.

    If the into parameter contains the GET_uid_value request parameter, as shown in the following example, then the payload will be inserted into the GET_uid_value parameter but not the HEADER_COOKIE_value parameter.

      - 'GET_uid_value'

    Because the following example contains only one parameter, the into parameter value may be written in one line:

    into: 'GET_uid_value'

  • method — this optional parameter specifies the list of the methods that will be used to insert the payload into the baseline request element.

    • prefix — insert the payload before the baseline request element value.
    • postfix — insert the payload after the baseline request element value.
    • random — insert the payload into a random place in the baseline request element value.
    • replace — replace the baseline request element value with the payload.

    Payload insertion methods

    If the method parameter is absent, the replace method will be used by default.

    The number of test requests created depends on the number of specified methods: one test request per insertion method.

    For example, if the following insertion methods are specified:

      - prefix
      - replace

    then for a single payload, two test requests are created; for two payloads, four test requests are created (two test requests for each payload), and so on.

  • The payload parameter specifies the list of payloads to be inserted into the request parameter to create a test request that will then test the target application for vulnerabilities.

    This parameter is obligatory, and it should always be present in the section. The list should contain at least one payload. If there are multiple payloads, the FAST node sequentially inserts payloads into the request parameter and tests the target application for vulnerabilities using each of the test requests created.

    Payload generation

    The payload is a string that is inserted into one of the parameters during the request processing.

    Example of multiple payloads
      - "') or 1=('1"
      - "/%5c../%5c../%5c../%5c../%5c../%5c../%5c../etc/passwd/"

    You can use special markers as a part of the payload to further expand the possibilities of vulnerability detection:

    • STR_MARKER — insert a random string into the payload exactly in the position where the STR_MARKER is specified.

      For example, the STR_MARKER can be used to check the application for an XXS vulnerability.



    • CALC_MARKER — insert a string containing a random arithmetic expression (for example, 1234*100) into the payload exactly in the position where the CALC_MARKER is specified.

      For example, the CALC_MARKER can be used to check the application for an RCE vulnerability.


      '; bc <<< CALC_MARKER'

    • DNS_MARKER — insert a string containing a random domain (for example, into the payload exactly in the position where the DNS_MARKER is specified.

      For example, the DNS_MARKER can be used to check the application for DNS Out-of-Bound vulnerabilities.


      '; ping DNS_MARKER'

    Markers operation logic

    If the Detect phase detects a marker from any payload in the server's response, then the attack is successful, meaning that the vulnerability was successfully exploited. To see detailed information about the Detect phase operating with markers, proceed to this link.