Acunetix - Cross-site Scripting

[goestin820]

Target URL	http://testphp.vulnweb.com
Target Description	test
Severity	High

Affects

http://testphp.vulnweb.com/guestbook.php

Attack Details

URL encoded POST input name was set to anonymous user'"()&%<zzz><ScRiPt >5zAJ(9108)</ScRiPt>

HTTP Request

POST /guestbook.php HTTP/1.1
Acunetix-Aspect: enabled
Acunetix-Aspect-Password: 082119f75623eb7abd7bf357698ff66c
Acunetix-Aspect-ScanID: 8869956492605776042
Content-Type: application/x-www-form-urlencoded
Referer: http://testphp.vulnweb.com/
Content-Length: 96
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Encoding: gzip,deflate,br
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/119.0.0.0 Safari/537.36
Host: testphp.vulnweb.com
Connection: Keep-alive
name=anonymous%20user'"()%26%255zAJ(9108)</ScRiPt>&submit=add%20message&text=555

Vulnerability Description

Cross-site Scripting (XSS) refers to client-side code injection attack wherein an attacker can execute malicious scripts into a legitimate website or web application. XSS occurs when a web application makes use of unvalidated or unencoded user input within the output it generates.

Impact

Malicious JavaScript has access to all the same objects as the rest of the web page, including access to cookies and local storage, which are often used to store session tokens. If an attacker can obtain a user's session cookie, they can then impersonate that user.

Furthermore, JavaScript can read and make arbitrary modifications to the contents of a page being displayed to a user. Therefore, XSS in conjunction with some clever social engineering opens up a lot of possibilities for an attacker.

Remediation

Apply context-dependent encoding and/or validation to user input rendered on a page

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References:

• Cross-site Scripting (XSS) Attack - Acunetix
• Types of XSS - Acunetix
• XSS Filter Evasion Cheat Sheet
• Excess XSS, a comprehensive tutorial on cross-site scripting
• Cross site scripting