用户提问: EXTRACTVALUE(1, CONCAT((SELECT super_priv FROM mysql.user WH...
Ai回答: This is a MySQL error-based SQL injection payload that exploits the `EXTRACTVALUE()` function to extract the `super_priv` value of the current database user from the `mysql.user` table.
How It Works:
1. `EXTRACTVALUE(1, ...)`
- This function expects an XML string as input, but `1` is not valid XML, forcing an error.
- The second argument (`CONCAT(...)`) triggers an error that leaks data from the database.
2. `CONCAT((SELECT super_priv FROM mysql.user WHERE user=(SELECT user) LIMIT 1))`
- The subquery retrieves the `super_priv` value (`Y` or `N`) for the current MySQL user.
- `LIMIT 1` ensures only one row is returned (prevents syntax errors).
3. Error Output Example:
```
XPATH syntax error: ':Y'
```
- If the current user has super privileges, the error will contain `:Y`.
- If not, it will show `:N`.
Why Is This Dangerous?
- Privilege Escalation:
- Attackers can check if the current DB user has `SUPER` privileges, which allow dangerous operations like file access (`LOAD_FILE`), command execution (`sys_exec`), and bypassing restrictions.
- Database Enumeration:
- Similar techniques can extract passwords (`authentication_string`), other users, or database schemas.
How to Prevent This Attack
# 1. Use Parameterized Queries (Prepared Statements)
- Never concatenate user input directly into SQL.
- Example (Python + MySQL):
```python
cursor.execute("SELECT * FROM users WHERE id = %s", (user_input,))
```
- PHP (PDO):
```php
$stmt = $pdo->prepare("SELECT * FROM users WHERE id = ?");
$stmt->execute([$user_input]);
```
# 2. Restrict Database Permissions
- Application DB users should not have `SELECT` access to `mysql.user`.
- Use the Principle of Least Privilege (PoLP).
# 3. Input Validation & Sanitization
- Block queries containing `EXTRACTVALUE`, `UPDATEXML`, `CONCAT(0x`, `char(`, etc.
- Use a Web Application Firewall (WAF) to filter malicious payloads.
# 4. Disable Error Leakage
- Configure MySQL to suppress detailed errors in production (`log_error_verbosity = 1`).
- Use generic error messages like _"Database error occurred"_ instead of exposing SQL details.
Similar Exploits to Watch For
- `UPDATEXML()` Injection
```sql
UPDATEXML(1, CONCAT(0x7e, (SELECT @@version), 1)
```
- `LOAD_FILE()` for File Disclosure
```sql
SELECT LOAD_FILE('/etc/passwd');
```
- `INTO OUTFILE` for File Writing
```sql
SELECT 'malicious code' INTO OUTFILE '/var/www/shell.php';
```
Final Thoughts
This payload is a clear sign of SQL injection probing. If you see it in logs, your system may be vulnerable.
✅ Fix: Switch to parameterized queries and restrict DB permissions.
🔍 Test: Use tools like `sqlmap` (ethically) to check for vulnerabilities.
Need help securing your database? Let me know! 🔐
0
IP地址: 113.207.49.73
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提问时间: 2025-06-16 18:54:08
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