htcap is a web application scanner able to crawl single page application (SPA) in a recursive manner by intercepting ajax calls and DOM changes.
Htcap is not just another vulnerability scanner since it's focused on the crawling process and uses external tools to discover vulnerabilities. It's designed to be a tool for both manual and automated penetration test of modern web applications.

The scan process is divided in two parts, first htcap crawls the target and collects as many requests as possible (urls, forms, ajax ecc..) and saves them to a sql-lite database. When the crawling is done it is possible to launch several security scanners against the saved requests and save the scan results to the same database.
When the database is populated (at least with crawing data), it's possible to explore it with ready-available tools such as sqlite3 or DBEaver or export the results in various formats using the built-in utilities.


Let's assume that we have to perform a penetration test against target.local, first we crawl the site:

$ htcap/ crawl target.local target.db

Once the crawl is done, the database (target.db) will contain all the requests discovered by the crawler. To explore/export the database we can use the htcap utilities or ready available tools. For example, to list all discovered ajax calls we can use a single shell command:

$ echo "SELECT method,url,data FROM request WHERE type = 'xhr';" | sqlite3 target.db


$ htcap/ util lsajax target.db

Now that the site is crawled it's possible to launch several vulnerability scanners against the requests saved to the database. A scanner is an external program that can fuzz requests to spot security flaws.

Htcap uses a modular architecture to handle different scanners and execute them in a multi-threaded environment. For example we can run ten parallel instances of sqlmap against saved ajax requests with the following command:

$ htcap/ scan -r xhr -n 10 sqlmap target.db

Htcap comes with sqlmap and arachni modules built-in.
Sqlmap is used to discover SQL-Injection vulnerabilities and arachni is used to discover XSS, XXE, Code Executions, File Inclusions ecc.
Since scanner modules extend the BaseScanner class, they can be easly created or modified (see the section "Writing Scanner Modules" of this manual).

Htcap comes with several tools to export the crawl and scan results.
For example we can generate an interactive report containing the relevant informations about website/webapp with the command below.
Relevant informations will include, for example, the list of all pages that trigger ajax calls or websockets and the ones that contain vulnerabilities.

$ htcap/ util report target.db target.html

For a list of discovered vulnerabilities use the "lsvuln" utility

$ htcap/ util lsvuln target.db



  1. Python 2.7
  2. PhantomJS v2
  3. Sqlmap (for sqlmap scanner module)
  4. Arachni (for arachni scanner module)

Download and Run

$ git clone htcap
$ htcap/

Alternatively you can download the latest zip here.

PhantomJs can be downloaded here. It comes as a self-contained executable with all libraries linked statically, so there is no need to install or compile anything else.
Htcap will search for phantomjs executable in the locations listed below and in the paths listed in $PATH environment varailbe:

  1. ./
  2. /usr/bin/
  3. /usr/local/bin/
  4. /usr/share/bin/

To install htcap system-wide:

# mv htcap /usr/share/
# ln -s /usr/share/htcap/ /usr/local/bin/htcap

Quick Scan Script

To perform a vulnerability assessment with htcap you have to execute at last three commands: one to execute the crawler, one to run a scanner and one to generate the report. To speed up this process, htcap comes with a bash script that automates this process. It can also be installed system-wide by creating a link to /usr/local/bin.

# ln -s /usr/share/htcap/scripts/ /usr/local/bin/htcapquick
$ htcapquick target.local


You can find an online demo of the html report here and a screenshot of the database view here
You can also explore the test pages here to see from what the report has been generated. They also include a page to test ajax recursion.


In order to read the database it's possible to use the built-in utilities or any ready-available sqlite3 client.


Generate the html report. (demo report available here)

$ htcap/ util report target.db target.html

List all pages that trigger ajax requests:

$ htcap/ util lsajax target.db
    Request ID: 6
    Page URL:   http://target.local/dashboard
    Referer:    http://target.local/
    Ajax requests:
      [BUTTON txt=Statistics].click() -> GET http://target.local/api/get_stats

List all discovered SQL-Injection vulnerabilities:

$ htcap/ util lsvuln target.db "type='sqli'"
    C O M M A N D
    python /usr/local/bin/sqlmap --batch -u http://target.local/api/[...]

    D E T A I L S
    Parameter: name (POST)
        Type: error-based
        Title: PostgreSQL AND error-based - WHERE or HAVING clause
        Payload: id=1' AND 4163=CAST [...]


Search for login forms

SELECT referer, method, url, data FROM request WHERE type='form' AND (url LIKE '%login%' OR data LIKE '%password%')

Search inside the pages html

SELECT url FROM request WHERE html LIKE '%upload%' COLLATE NOCASE


Htcap features an algorithm able to crawl ajax-based pages in a recursive manner.
The algorithm works by capturing ajax calls, mapping DOM changes to them and repeat the process recursively against the newly added elements.
When a page is loaded htcap starts by triggering all events and filling input values in the aim to to trigger ajax calls. When an ajax call is detected, htcap waits until it is completed and the relative callback is called; if, after that, the DOM is modified, htcap runs the same algorithm against the added elements and repeats it until all the ajax calls have been fired.

|                 |
|load page content|
|  interact with  |
|  new content    |<-----------------------------------------+
'--------,--------'                                          |
         |                                                   |
         |                                                   |
         |                                                   | YES
   ______V______             ________________          ______l_____
 /     AJAX      \ YES      |                |       /    CONTENT   \
{    TRIGGERED?   }-------->|   wait ajax    |----->{    MODIFIED?   }
 \ ______ ______ /          '----------------'       \ ______ _____ /
         | NO                                                | NO
         |                                                   |
         |                                                   |
 ________V________                                           |
|                 |                                          |
|     return      |<-----------------------------------------+


$ htcap crawl -h
usage: htcap [options] url outfile
  -h               this help
  -w               overwrite output file
  -q               do not display progress informations
  -v               be verbose
  -m MODE          set crawl mode:
                      - passive: do not intract with the page
                      - active: trigger events
                      - aggressive: also fill input values and crawl forms (default)
  -s SCOPE         set crawl scope
                      - domain: limit crawling to current domain (default)
                      - directory: limit crawling to current directory (and subdirecotries)
                      - url: do not crawl, just analyze a single page
  -D               maximum crawl depth (default: 100)
  -P               maximum crawl depth for consecutive forms (default: 10)
  -F               even if in aggressive mode, do not crawl forms
  -H               save HTML generated by the page
  -d DOMAINS       comma separated list of allowed domains (ex *
  -c COOKIES       cookies as json or name=value pairs separaded by semicolon
  -C COOKIE_FILE   path to file containing COOKIES
  -r REFERER       set initial referer
  -x EXCLUDED      comma separated list of urls to exclude (regex) - ie logout urls
  -p PROXY         proxy string protocol:host:port -  protocol can be 'http' or 'socks5'
  -n THREADS       number of parallel threads (default: 10)
  -A CREDENTIALS   username and password used for HTTP authentication separated by a colon
  -U USERAGENT     set user agent
  -t TIMEOUT       maximum seconds spent to analyze a page (default 300)
  -u USER_SCRIPT   inject USER_SCRIPT into any loaded page
  -S               skip initial checks
  -G               group query_string parameters with the same name ('[]' ending excluded)
  -N               don't normalize URL path (keep ../../)
  -R               maximum number of redirects to follow (default 10)
  -I               ignore robots.txt
  -O               dont't override timeout functions (setTimeout, setInterval)

Crawl Modes

Htcap supports three scan modes: passive, active and aggressive.
When in passive mode, htcap do not interacts with the page, this means that no events are triggered and only links are followed. In this mode htcap acts as a very basic web crawler that collects only the links found in the page (A tags). This simulates a user that just clicks on links.
The active mode behaves like the passive mode but it also triggers all discovered events. This simulates a user that interact with the page without filling input values.
The aggressive mode makes htcap to also fill input values and post forms. This simulates a user that performs as many actions as possible on the page.


Crawl trying to be as stealth as possible

$ htcap/ crawl -m passive target.db

Crawl Scope

Htcap limits the crawling process to a specific scope. Available scopes are: domain, directory and url.
When scope is set to domain, htcap will crawl the domain of the taget only, plus the allowed_domains (-d option).
If scope is directory, htcap will crawl only the target directory and its subdirectories and if the scope is url, htcap will not crawl anything, it just analyzes a single page.
The excluded urls (-x option) are considered out of scope, so they get saved to database but not crawled.


Crawl all discovered subdomains of http://target.local plus http://www.target1.local starting from

$ htcap/ crawl -d '*.target.local,www.target1.local' target.db

Crawl the directory admin and never go to the upper directory level

$ htcap/ crawl -s directory target.db

Excluded Urls

It's possible to exclude some urls from crawling by providing a comma separated list of regular expression. Excluded urls are considered out of scope.

$ htcap/ crawl -x '.*logout.*,.*session.*' target.db

Crawl depth

htcap is designed to limit the crawl depth to a specific threshold.
By default there are two depth limits, one for general crawling (-D) and the other for sequential post request (-P).


Cookies can be specified both as json and as string and can be passed as commandline option or inside a file.
The json must be set as follow, and only the 'name' and 'value' properties are mandatory.


The string format is the classic list of name=value pairs separated by a semicolon:

session=eyJpdiI6IkZXV1J; version=1.1

A quick note about encoding: if cookies are passed as string their value gets url-decoded. This means that to put, for example, a semicolon into the cookie value it must be urlencoded.


$ htcap/ crawl -c 'session=someBetter%3BToken; version=1' target.db'
$ htcap/ crawl -c '[{name:"session",value:"someGood;Token"}]' target.db'
$ htcap/ crawl -C cookies.json target.db'


Htcap's database is composed by the tables listed below

CRAWL_INFOCrawl informations
REQUESTContains the requests discovered by the crawler
REQUEST_CHILDRelations between requests
ASSESSMENTEach scanner run generates a new assessment
VULNERABILITYVulnerabilities discovered by an assessment


The CRAWL_INFO table contains the informations about the crawl and, since each crawl has its own database, it contains one row only. It's composed by the following fields:

HTCAP_VERSIONVersion of htcap
START_DATECrawl start date
END_DATECrawl end date
COMMANDLINECrawler commandline options
USER_AGENTUser-agent set by the crawler


The REQUEST table contains all the requests discovered by the crawler.
It's composed by the following fields:

ID Id of the request
ID_PARENT Id of the parent request
TYPE The type of the request
METHOD Request method
URL Request URL
REDIRECTS Number of redirects ahead of this page
COOKIES Cookies as json
HTTP_AUTH Username:password used for basic http authentication
OUT_OF_SCOPE Equal to 1 if the URL is out of crawler scope
TRIGGER The html element and event that triggered the request
CRAWLED Equal to 1 if the request has been crawled
CRAWLER_ERRORS Array of crawler errors as json
HTML HTML generated by the page
USER_OUTPUT Array of user messages as Json - see ui.print() of User Script

The parent request is the request from wich the main request has been generated. For example, each request inherits the cookies from the parent.
Consider that the crawler follows just one path, this means that if page A is linked from page B and page C, the crawler will load page A as if the navigation comes from page B but not from page C. To save all the connections between pages, the crawler uses a separate table.
This table, called REQUEST_CHILD, contains the following fields:

ID_REQUEST Id of the parent request
ID_CHILD Id of the child request

By combining these two tables it's possible to rebuild the whole site structure.


Each scaner run generates a new record in this table to save the scanning informations, so basically an assessment is considered the execution of a scanner module.
It contains the following fields:

IDId of the assessment
SCANNERThe name of the scanner
START_DATEScan start date
END_DATEScan end date


The VULNERABILITY table contains all the vulnerabilities discovered by the various assessments. It contains the following fields:

IDId of the vulnerability
ID_ASSESSMENTId of the assessment to which it belongs to
ID_REQUESTId of the request that has been scanned
TYPEvulnerability type (see vulntypes)
DESCRIPTIONDescription of the vulnerability


Each scanner module is a python class that extends the BaseScanner class and overrides the following methods:

  • init
  • get_settings
  • get_cmd
  • scanner_executed

Basically the execution process of a scanner is as follow:

  1. Scanner is initalized by the parent class by calling the get_settings and init methods
  2. The parent class calls the get_cmd method to get the command to execute for the given request
  3. Once the command returns, the parent class passes the the output to the scanner module by calling the scanner_executed method.
  4. The scanner_executed method parses the command output and saves the result to the database by calling the save_vulnerability method.

Basic Module Example

from core.scan.base_scanner import BaseScanner

class Curl(BaseScanner):
  def init(self, argv):

  def get_settings(self):
    return dict(
      request_types = "link,redirect",
      num_threads = 10,
      process_timeout = 20,
      scanner_exe = "/usr/bin/env curl"

  def get_cmd(self, request, tmp_dir):
    cmd = ["-I", request.url]
    return cmd

  def scanner_executed(self, request, out, err, tmp_dir, cmd):
    if not"^X-XSS-Protection\:", out, re.M):
      type  = "xss-portection-missing"
      descr = "X-XSS-Protection header is not set"
      self.save_vulnerability(request, type, descr)

Adding A Module

To add a scanner module called, for example, myscanner follow these steps:

  1. Create a file named inside core/scan/scanners/
  2. Inside that file create Myscanner class that overrides BaseScanner
  3. Override methods and adjust settings

To execute myscanner run the following command:

$ htcap/ scan myscanner target.db

URL Uniqueness

One of the biggest problem when scanning a webapplication is how to determine the uniqueness of a page. Modern web applications usually use the same page to generate different contents based to the url parameters or patterns. A vulnerability scanner don't need to analyze the same page just because its content has changed.
In the aim to solve this problem, or at least reduce its impact, htcap implements an algorithm for url comparision that can let scanner modules skip "duplicated" urls.
Inside the get_cmd method it's possbile to implement this feature using the code below.

if self.is_request_duplicated(request):
    return False

The algorithm is extreamely simple, it just removes the values from parameters and it sorts them alphabetically; for example http://www.test.local/a/?c=1&a=2&b=3 becames http://www.test.local/a/?a=&b=&c= .
A good idea would be the use of the SimHash algorithm but lots of tests are needed.
In case of POST requests the same algorithm is also applied to the following payloads:

  1. URL-Encoded
  2. XML
  3. JSON

Detailed Module Example:

from core.scan.base_scanner import BaseScanner

class CustomScanner(BaseScanner):

  def init(self, argv):
    custom initializer
    the first argument is an array of command line arguments (if any) passed to the scanner
    if argv[0] == "-h":
      print "usage: ...."

  def get_settings(self):
    scanner settings

    return dict(
      request_types = "xhr,link,redirect,form,jsonp", # request types to analyze
      num_threads = 10, # number of parallel commands to execute
      process_timeout = 180, # command execution timeout
      scanner_exe = "/usr/bin/customscanner"

  def get_cmd(self, request, tmp_dir):
    this method is called by the parent class to get the command to execute
    the first argument is the Request object containing the url, the cookies ecc
    the second argument is the path to the temporary dir used to store output files ecc

    if self.is_request_duplicated(request):
        return False

    out_file = tmp_dir + "/output"
    cmd = [
      "--url", request.url,
      "--out", out_file

    # return False to skip current request
    #return False

    return cmd

  def scanner_executed(self, request, out, err, tmp_dir, cmd):
    this method is called when the execution of a command is completed
    the first argument is the Request object used to generate the command
    the second and the third are the output and the error returned by the command
    the forth argumnt is the path to the temporary dir used by the command
    the fifth argument is the command executed

    out_file = tmp_dir + "/output"

    with open(out_file,'r') as file:
      output =

    # parse output

    for vulnerability in report:
      # request, type, description
      self.save_vulnerability(request, "sqli", vulnerability)

Scan scope

Scanner modules analyze only in-scope requests. If the crawler scope is set to "url", any discovered request will be considered out of scope, including ajax requests, jsonp ecc.
For example if target.local/foo/bar.php has been crawled with scope set to "url" and it contains ajax request to target.local/foo/ajax.php, they won't be scanned. With a simple query it's possible to make those request visible to scanners.

UPDATE request set out_of_scope=0 where type in ('xhr','websocket','jsonp')

User Script (experimental)

Htcap allows the user to script the page analysis by using the so called User Script (-u option).
When htcap analyzes a page it triggers some hooks to let the user customize the analysis behaviour. For example an hook is called before any XHR request and the user can deceide if it must be performed or cancelled.

A reference to the UI object is passed to all hooks, the purposes of this object are:

  • Let the user store variables inside the ui.vars object
  • Let the user access the request id via
  • Let the user call some methods to interact with the page.
    Actually the available methods are:
    • ui.pageEval(function) - evaluate function in the context of the webpage (no scope chain available)
    • ui.print(message) - save a per-request user message into the request table
    • ui.fread(path_to_file) - read from file
    • ui.fwrite(path_to_file, content, [mode='w']) - write to file
    • ui.render(path_to_file) - save a screenshot of the page current state

Available hooks are:

  • onInit - called when the page is initialized
  • onStart - called before the analysis starts
  • onTriggerEvent - called before triggering an avent
  • onEventTriggered - called afted event has been fired
  • onFillInput - called before filling an input element
  • onXhr - called before XHR requests
  • onAllXhrsCompleted - called when all XHRs are completed
  • onDomModified - called when the DOM is modified
  • onEnd - called before exit

User Script Example:

ui Methods:
    ui.pageEval(function) - evaluate function in the context of the webpage (no scope chain available)
    ui.print(message) - save a per-request user message into the request table
    ui.fread(path_to_file) - read from file
    ui.fwrite(path_to_file, content, mode) - write to file
    ui.render(path_to_file) - save a screenshot of the page current state

 US = {
  onInit: function(ui){
    // init local variables
    ui.vars.cnt = 0;

    // override native methods
        window.prompt = function(){ return "AAA" };

  onStart: function(ui){

  onTriggerEvent: function(ui){
    var ok = ui.pageEval(function(element, event){
        if(event == "click" && element.className == 'kill'){
            return false;
        return true;
    // cancel triggering of event
    if(!ok) return false;

  onEventTriggered: function(ui){
    ui.pageEval(function(element, event){});

  onXhr: function(ui){
    var url = ui.pageEval(function(request){
        return request.url;
    // cancel XHR request if url matches XXX
        ui.print("Skipped XHR to " + url)
        return false;
  onFillInput: function(ui){
    // here it's possible to force a value or prevent it to be filled
    // WARNING: do NOT set dynamic values! for instance something like
    //  element.value = Math.random()
    // will lead to INFINITE CRAWLING if you crawl forms
    return ui.pageEval(function(element){
        if( == "car_vendor"){
            element.value = "Ferrari";
            // prevent element value to be set
            return false;
  onAllXhrsCompleted: function(ui){

  onDomModified: function(ui){
    ui.pageEval(function(rootElements, allElements){});
    // save a screenshot on every DOM change
    ui.render( + "-screen-" + ui.vars.cnt + ".png");

  onEnd: function(ui){


Htcap has been written by Filippo Cavallarin.
Please report bugs, comments ecc to filippo.cavallarin[]


This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or(at your option) any later version.