# 2479 Vulnerability Patterns 2d771fb2

> Security Vulnerability Patterns

- Skill: `tools-only/2479-vulnerability-patterns-2d771fb2` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds@latest add tools-only/2479-vulnerability-patterns-2d771fb2`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tools-only/2479-vulnerability-patterns-2d771fb2/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Security
- Author: tools-only (https://skillmd.com/u/tools-only)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/tools-only/2479-vulnerability-patterns-2d771fb2

---

# Security Vulnerability Patterns

This reference catalogs common security vulnerability patterns, insecure coding idioms, and historical CVE-style patterns with detection techniques and exploitability assessment.

## Table of Contents

1. [Injection Vulnerabilities](#injection-vulnerabilities)
2. [Authentication and Session Management](#authentication-and-session-management)
3. [Cross-Site Scripting (XSS)](#cross-site-scripting-xss)
4. [Insecure Deserialization](#insecure-deserialization)
5. [Path Traversal](#path-traversal)
6. [Buffer Overflow](#buffer-overflow)
7. [Cryptographic Failures](#cryptographic-failures)
8. [Access Control Issues](#access-control-issues)
9. [Server-Side Request Forgery (SSRF)](#server-side-request-forgery-ssrf)
10. [XML External Entity (XXE)](#xml-external-entity-xxe)
11. [Race Conditions](#race-conditions)
12. [Command Injection](#command-injection)
13. [Exploitability Assessment](#exploitability-assessment)

## Injection Vulnerabilities

### Pattern 1: SQL Injection

**Detection:**
- String concatenation in SQL queries
- User input directly embedded in queries
- No parameterized queries or prepared statements

**Example (Python):**
```python
# VULNERABLE
def get_user(username):
    query = "SELECT * FROM users WHERE username = '" + username + "'"
    cursor.execute(query)
```

**Why Risky:**
Attacker can inject SQL code to:
- Bypass authentication
- Extract sensitive data
- Modify or delete data
- Execute administrative operations

**Exploitation Conditions:**
- User input reaches SQL query
- No input validation or sanitization
- Database errors exposed to user

**Safe Pattern:**
```python
# SAFE
def get_user(username):
    query = "SELECT * FROM users WHERE username = ?"
    cursor.execute(query, (username,))
```

### Pattern 2: NoSQL Injection

**Detection:**
- Direct object construction from user input
- No input validation for MongoDB/NoSQL queries
- User input in query operators ($where, $regex, etc.)

**Example (JavaScript):**
```javascript
// VULNERABLE
app.post('/login', (req, res) => {
    db.users.findOne({ username: req.body.username, password: req.body.password });
});
```

**Why Risky:**
Attacker can inject query operators like `{$ne: null}` to bypass authentication.

**Exploitation Conditions:**
- User input directly used in NoSQL queries
- No type validation
- Query operators not sanitized

### Pattern 3: LDAP Injection

**Detection:**
- String concatenation in LDAP filters
- User input in LDAP queries without escaping

**Example (Java):**
```java
// VULNERABLE
String filter = "(uid=" + username + ")";
NamingEnumeration results = ctx.search("ou=users", filter, controls);
```

**Why Risky:**
Attacker can modify LDAP queries to access unauthorized data.

**Exploitation Conditions:**
- User input in LDAP filter
- No special character escaping
- LDAP errors exposed

## Authentication and Session Management

### Pattern 4: Hardcoded Credentials

**Detection:**
- Passwords, API keys, tokens in source code
- Credentials in configuration files committed to version control
- Secrets in environment variable defaults

**Example (Python):**
```python
# VULNERABLE
API_KEY = "sk-1234567890abcdef"
DATABASE_PASSWORD = "admin123"
```

**Why Risky:**
- Credentials exposed in version control history
- Anyone with code access can authenticate
- Difficult to rotate compromised credentials

**Exploitation Conditions:**
- Code repository is public or leaked
- Credentials still valid
- No additional authentication factors

### Pattern 5: Weak Session Management

**Detection:**
- Predictable session IDs
- Session IDs in URLs
- No session expiration
- Session fixation vulnerabilities

**Example (PHP):**
```php
// VULNERABLE
session_id($_GET['sessionid']); // Session fixation
session_start();
```

**Why Risky:**
Attacker can hijack user sessions or fix session IDs.

**Exploitation Conditions:**
- Session ID predictable or exposed
- No session regeneration after login
- Long or infinite session lifetime

### Pattern 6: Insecure Password Storage

**Detection:**
- Plain text password storage
- Weak hashing algorithms (MD5, SHA1)
- No salt or weak salt
- Insufficient iteration count

**Example (Java):**
```java
// VULNERABLE
String hashedPassword = MessageDigest.getInstance("MD5").digest(password.getBytes());
```

**Why Risky:**
Passwords can be recovered through rainbow tables or brute force.

**Exploitation Conditions:**
- Database breach
- Weak hashing algorithm
- No or predictable salt

## Cross-Site Scripting (XSS)

### Pattern 7: Reflected XSS

**Detection:**
- User input directly rendered in HTML
- No output encoding/escaping
- innerHTML or similar DOM manipulation with user data

**Example (JavaScript):**
```javascript
// VULNERABLE
document.getElementById('result').innerHTML = "Hello " + req.query.name;
```

**Why Risky:**
Attacker can inject JavaScript to steal cookies, session tokens, or perform actions as the victim.

**Exploitation Conditions:**
- User input reflected in response
- No Content-Security-Policy
- Sensitive data in cookies/localStorage

### Pattern 8: Stored XSS

**Detection:**
- User input stored and displayed without sanitization
- Rich text editors without proper filtering
- User-generated content rendered as HTML

**Example (Python/Flask):**
```python
# VULNERABLE
@app.route('/comment', methods=['POST'])
def add_comment():
    comment = request.form['comment']
    db.save_comment(comment)
    return render_template('comments.html', comment=comment)
```

**Why Risky:**
Persistent attack affecting all users viewing the content.

**Exploitation Conditions:**
- Stored data rendered without encoding
- Multiple users access the content
- No input validation or output encoding

### Pattern 9: DOM-based XSS

**Detection:**
- Client-side JavaScript using unsafe sinks (innerHTML, eval, document.write)
- User-controlled data from URL fragments, postMessage
- No sanitization before DOM manipulation

**Example (JavaScript):**
```javascript
// VULNERABLE
let userInput = location.hash.substring(1);
eval(userInput);
```

**Why Risky:**
Entirely client-side attack, bypassing server-side protections.

**Exploitation Conditions:**
- Unsafe sink with user-controlled source
- No client-side validation
- Sensitive operations in JavaScript

## Insecure Deserialization

### Pattern 10: Unsafe Deserialization

**Detection:**
- Deserializing untrusted data
- pickle, yaml.load, unserialize without validation
- Java ObjectInputStream with untrusted data

**Example (Python):**
```python
# VULNERABLE
import pickle
user_data = pickle.loads(request.data)
```

**Why Risky:**
Attacker can execute arbitrary code during deserialization.

**Exploitation Conditions:**
- Application deserializes user input
- Gadget chains available in classpath
- No integrity checks on serialized data

**Safe Pattern:**
```python
# SAFE
import json
user_data = json.loads(request.data)
```

## Path Traversal

### Pattern 11: Directory Traversal

**Detection:**
- File paths constructed from user input
- No path validation or sanitization
- Direct file access with user-controlled names

**Example (Node.js):**
```javascript
// VULNERABLE
app.get('/download', (req, res) => {
    let filename = req.query.file;
    res.sendFile('/uploads/' + filename);
});
```

**Why Risky:**
Attacker can access files outside intended directory using `../` sequences.

**Exploitation Conditions:**
- User controls file path
- No path canonicalization
- Sensitive files accessible

## Buffer Overflow

### Pattern 12: Stack Buffer Overflow

**Detection:**
- Unsafe C functions (strcpy, sprintf, gets)
- No bounds checking on buffer writes
- Fixed-size buffers with variable-length input

**Example (C):**
```c
// VULNERABLE
void process_input(char *user_input) {
    char buffer[64];
    strcpy(buffer, user_input);  // No bounds check
}
```

**Why Risky:**
Attacker can overwrite return addresses, execute arbitrary code.

**Exploitation Conditions:**
- No stack canaries or ASLR
- Executable stack
- Attacker controls input length

### Pattern 13: Heap Buffer Overflow

**Detection:**
- malloc/new without size validation
- Off-by-one errors in loops
- Integer overflow in size calculations

**Example (C++):**
```cpp
// VULNERABLE
int size = user_size;
char *buffer = new char[size];
memcpy(buffer, user_data, user_length);  // user_length > size
```

**Why Risky:**
Heap metadata corruption, arbitrary code execution.

**Exploitation Conditions:**
- Heap exploitation techniques available
- Attacker controls size or data
- No heap protections

## Cryptographic Failures

### Pattern 14: Weak Encryption

**Detection:**
- DES, RC4, or other deprecated algorithms
- ECB mode for block ciphers
- Small key sizes (< 128 bits)

**Example (Java):**
```java
// VULNERABLE
Cipher cipher = Cipher.getInstance("DES/ECB/PKCS5Padding");
```

**Why Risky:**
Encrypted data can be decrypted through cryptanalysis.

**Exploitation Conditions:**
- Sufficient ciphertext available
- Known plaintext attacks possible
- Weak algorithm or mode

### Pattern 15: Insecure Random Number Generation

**Detection:**
- Using non-cryptographic RNGs for security (rand(), Math.random())
- Predictable seeds
- Insufficient entropy

**Example (Python):**
```python
# VULNERABLE
import random
session_token = ''.join(random.choices(string.ascii_letters, k=32))
```

**Why Risky:**
Predictable tokens can be guessed or brute-forced.

**Exploitation Conditions:**
- Attacker can observe multiple tokens
- Seed is predictable
- Used for security-critical operations

**Safe Pattern:**
```python
# SAFE
import secrets
session_token = secrets.token_urlsafe(32)
```

### Pattern 16: Missing Certificate Validation

**Detection:**
- SSL/TLS certificate validation disabled
- Accepting self-signed certificates
- No hostname verification

**Example (Python):**
```python
# VULNERABLE
import ssl
context = ssl._create_unverified_context()
urllib.request.urlopen(url, context=context)
```

**Why Risky:**
Man-in-the-middle attacks possible.

**Exploitation Conditions:**
- Network traffic interceptable
- Attacker can present fake certificate
- Sensitive data transmitted

## Access Control Issues

### Pattern 17: Insecure Direct Object Reference (IDOR)

**Detection:**
- User IDs or object IDs in URLs/parameters
- No authorization check before data access
- Predictable or sequential identifiers

**Example (Python/Flask):**
```python
# VULNERABLE
@app.route('/user/<user_id>')
def get_user(user_id):
    return db.get_user(user_id)  # No auth check
```

**Why Risky:**
Attacker can access other users' data by changing IDs.

**Exploitation Conditions:**
- No authorization checks
- Predictable identifiers
- Sensitive data accessible

### Pattern 18: Missing Function-Level Access Control

**Detection:**
- Admin functions accessible without role check
- Client-side access control only
- No server-side authorization

**Example (JavaScript/Express):**
```javascript
// VULNERABLE
app.post('/admin/delete-user', (req, res) => {
    deleteUser(req.body.userId);  // No admin check
});
```

**Why Risky:**
Privilege escalation, unauthorized administrative actions.

**Exploitation Conditions:**
- Attacker knows endpoint
- No authentication or authorization
- Sensitive operations exposed

## Server-Side Request Forgery (SSRF)

### Pattern 19: SSRF via URL Parameter

**Detection:**
- User-controlled URLs in HTTP requests
- No URL validation or allowlist
- Internal network accessible

**Example (Python):**
```python
# VULNERABLE
@app.route('/fetch')
def fetch_url():
    url = request.args.get('url')
    response = requests.get(url)
    return response.content
```

**Why Risky:**
Attacker can access internal services, cloud metadata endpoints.

**Exploitation Conditions:**
- Application makes requests to user URLs
- Internal network accessible
- Cloud metadata available (169.254.169.254)

### Pattern 20: SSRF via File Upload

**Detection:**
- Processing URLs in uploaded files (XML, SVG, PDF)
- No validation of external references
- XXE combined with SSRF

**Why Risky:**
Bypass network restrictions, access internal resources.

**Exploitation Conditions:**
- File processing follows external references
- Internal network accessible
- No URL filtering

## XML External Entity (XXE)

### Pattern 21: XXE Injection

**Detection:**
- XML parsing with external entities enabled
- No DTD validation disabled
- User-controlled XML input

**Example (Java):**
```java
// VULNERABLE
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(userXmlInput);
```

**Why Risky:**
File disclosure, SSRF, denial of service.

**Exploitation Conditions:**
- External entities not disabled
- File system accessible
- XML parser processes DTDs

**Safe Pattern:**
```java
// SAFE
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
factory.setFeature("http://xml.org/sax/features/external-general-entities", false);
factory.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
DocumentBuilder builder = factory.newDocumentBuilder();
```

## Race Conditions

### Pattern 22: Time-of-Check Time-of-Use (TOCTOU)

**Detection:**
- File operations with check-then-use pattern
- Shared resource access without locking
- Non-atomic operations on critical data

**Example (C):**
```c
// VULNERABLE
if (access(filename, W_OK) == 0) {
    // File is writable
    fd = open(filename, O_WRONLY);  // Race window here
    write(fd, data, size);
}
```

**Why Risky:**
Attacker can modify file between check and use.

**Exploitation Conditions:**
- Shared file system
- Predictable timing
- Privileged process

### Pattern 23: Race Condition in Web Applications

**Detection:**
- Non-atomic database operations
- No transaction isolation
- Concurrent access to shared state

**Example (Python):**
```python
# VULNERABLE
balance = db.get_balance(user_id)
if balance >= amount:
    db.set_balance(user_id, balance - amount)  # Race here
```

**Why Risky:**
Double-spending, inconsistent state.

**Exploitation Conditions:**
- Concurrent requests possible
- No locking or transactions
- Financial or critical operations

## Command Injection

### Pattern 24: OS Command Injection

**Detection:**
- User input in system(), exec(), shell commands
- No input validation or escaping
- Shell metacharacters not filtered

**Example (PHP):**
```php
// VULNERABLE
$filename = $_GET['file'];
system("cat /var/log/" . $filename);
```

**Why Risky:**
Arbitrary command execution on server.

**Exploitation Conditions:**
- User input reaches shell command
- Shell metacharacters not escaped
- Sufficient privileges

**Safe Pattern:**
```python
# SAFE
import subprocess
subprocess.run(['cat', '/var/log/' + filename], shell=False)
```

### Pattern 25: Code Injection

**Detection:**
- eval(), exec() with user input
- Dynamic code generation from user data
- Template injection

**Example (Python):**
```python
# VULNERABLE
user_code = request.form['code']
eval(user_code)
```

**Why Risky:**
Complete application compromise, arbitrary code execution.

**Exploitation Conditions:**
- User input in eval/exec
- No sandboxing
- Application privileges

## Exploitability Assessment

### Severity Levels

**Critical:**
- Remote code execution
- Authentication bypass
- Complete data breach
- System compromise

**High:**
- Privilege escalation
- Sensitive data exposure
- SQL injection with data access
- SSRF to internal services

**Medium:**
- XSS with session theft
- IDOR to user data
- Information disclosure
- Weak cryptography

**Low:**
- Information leakage
- Minor configuration issues
- Low-impact XSS
- Verbose error messages

### Exploitability Factors

**Attack Complexity:**
- Low: Simple exploit, no special conditions
- Medium: Requires specific conditions or timing
- High: Complex exploit chain, rare conditions

**Privileges Required:**
- None: Unauthenticated attack
- Low: Basic user account needed
- High: Administrative access required

**User Interaction:**
- None: Fully automated exploit
- Required: Victim must take action (click link, etc.)

**Impact:**
- Confidentiality: Data exposure
- Integrity: Data modification
- Availability: Service disruption

### CVE-Style Pattern Examples

**CVE-2021-44228 (Log4Shell):**
- Pattern: JNDI lookup in log messages
- Detection: `${jndi:ldap://` in user input reaching logger
- Exploitability: Critical, no authentication, remote code execution

**CVE-2017-5638 (Struts2):**
- Pattern: OGNL injection in Content-Type header
- Detection: Struts2 file upload with malformed Content-Type
- Exploitability: Critical, remote code execution

**CVE-2014-0160 (Heartbleed):**
- Pattern: Buffer over-read in TLS heartbeat
- Detection: OpenSSL 1.0.1 through 1.0.1f
- Exploitability: High, memory disclosure, no authentication

### Detection Confidence Levels

**High Confidence (90-100%):**
- Exact pattern match with known vulnerability
- Clear exploit path
- No mitigating controls

**Medium Confidence (60-89%):**
- Pattern resembles vulnerability
- Exploitation requires specific conditions
- Some mitigating controls present

**Low Confidence (30-59%):**
- Potential vulnerability
- Unclear exploit path
- Multiple mitigating factors
- Requires manual verification