Security Audit

Conduct a comprehensive security audit for the following [PROGRAMMING LANGUAGE] code.

**Check for these vulnerability categories:**

1. **Injection Attacks:** SQL Injection, Command Injection, LDAP Injection, XPath Injection
2. **Cross-Site Scripting (XSS):** Reflected, Stored, and DOM-based XSS
3. **Authentication & Authorization:** Weak password handling, missing permission checks
4. **Data Leaks:** Sensitive data in logs, unencrypted transmission, missing masking
5. **Cryptography:** Outdated algorithms, weak keys, insecure random numbers
6. **Input Validation:** Missing or insufficient input checks
7. **Session Management:** Session fixation, insecure cookies
8. **Dependencies:** Known vulnerabilities in used libraries

**Output Format:**
For each vulnerability found: Severity (Critical/High/Medium/Low), affected line, description, concrete fix with code example.

Code:
```[PROGRAMMING LANGUAGE]
[INSERT CODE HERE]
```

Replace placeholders in [square brackets]: [PROGRAMMING LANGUAGE][INSERT CODE HERE]