CVE-2026-31773

#!/usr/bin/env python3 # # PoC for CVE-2026-31773: Linux Kernel Bluetooth SMP Authentication Bypass # This script demonstrates the logic flaw where STK is marked as authenticated # even during a "Just Works" pairing (No MITM). # # Note: This is a conceptual simulation to verify the vulnerability logic. import bluetooth import time def simulate_vulnerable_pairing(): print("[*] Starting Bluetooth pairing simulation...") # Simulate the vulnerability condition in smp_random() # Vulnerable Logic: Check pending_sec_level instead of SMP_FLAG_MITM_AUTH pending_sec_level = "BT_SECURITY_HIGH" # Local device requests High Security smp_flag_mitm_auth = False # Actual pairing is Just Works (No MITM) print(f"[*] Local requested level: {pending_sec_level}") print(f"[*] Actual MITM protection status: {smp_flag_mitm_auth}") # --- Vulnerable Code Path --- if pending_sec_level == "BT_SECURITY_HIGH": stk_authenticated = True print("[!] VULNERABLE: STK marked as AUTHENTICATED based on pending_sec_level.") else: stk_authenticated = False # --- Secure Code Path (Patch) --- # if smp_flag_mitm_auth: # stk_authenticated_secure = True # else: # stk_authenticated_secure = False if stk_authenticated and not smp_flag_mitm_auth: print("[+] Exploit Successful: Key is marked authenticated without MITM protection.") print("[+] Impact: Attacker can access services requiring High Security.") return True else: print("[-] System behaves correctly.") return False if __name__ == "__main__": try: result = simulate_vulnerable_pairing() if result: print("\n[!] System is vulnerable to CVE-2026-31773") except Exception as e: print(f"Error: {e}")

{"cve": {"id": "CVE-2026-31773", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-05-01T15:16:40.587", "lastModified": "2026-05-11T20:38:06.777", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nBluetooth: SMP: derive legacy responder STK authentication from MITM state\n\nThe legacy responder path in smp_random() currently labels the stored\nSTK as authenticated whenever pending_sec_level is BT_SECURITY_HIGH.\nThat reflects what the local service requested, not what the pairing\nflow actually achieved.\n\nFor Just Works/Confirm legacy pairing, SMP_FLAG_MITM_AUTH stays clear\nand the resulting STK should remain unauthenticated even if the local\nside requested HIGH security. Use the established MITM state when\nstoring the responder STK so the key metadata matches the pairing result.\n\nThis also keeps the legacy path aligned with the Secure Connections code,\nwhich already treats JUST_WORKS/JUST_CFM as unauthenticated."}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 8.8, "baseSeverity": "HIGH", "attackVector": "ADJACENT_NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.8, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "NVD-CWE-noinfo"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.15.5", "versionEndExcluding": "3.16", "matchCriteriaId": "7AB7F235-CA17-4469-8F49-E61F880EF22E"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.16.1", "versionEndExcluding": "5.10.253", "matchCriteriaId": "0D5B310C-1F2B-40A6-BD8F-4AD7CA6B8B1D"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.11", "versionEndExcluding": "5.15.203", "matchCriteriaId": "20DDB3E9-AABF-4107-ADB0-5362AA067045"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.1.168", "matchCriteriaId": "E2DDDCA1-6DAB-4018-B920-8F045DDD8D3B"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.134", "matchCriteriaId": "F56F925B-BAF8-4F4B-B62F-1496AF19A307"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.81", "matchCriteriaId": "6EF80433-B33B-43C5-8E64-0FA7B8DCE1BC"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.22", "matchCriteriaId": "C9DF8BCE-36D3-475D-9D21-19E4F02F9029"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.12", "matchCriteriaId": "0A2B9540-02D5-41B4-B16A-82AF66FD4F36"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:3.16:-:*:*:*:*:*:*", "matchCriteriaId": "18374217-75DB-4E06-8293-8AAC0FD9D6C2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*", "matchCriteriaId": "F253B622-8837-4245-BCE5-A7BF8FC76A16"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*", "matchCriteriaId": "4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*", "matchCriteriaId": "F666C8D8-6538-46D4-B318-87610DE64C34"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*", "matchCriteriaId": "02259FDA-961B-47BC-AE7F-93D7EC6E90C2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*", "matchCriteriaId": "58A9FEFF-C040-420D-8F0A-BFDAAA1DF258"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*", "matchCriteriaId": "1D2315C0-D46F-4F85-9754-F9E5E11374A6"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/061ee71ac6b03c9f8432fe49538c3682bfcf4cf3", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/0afc846bd80073ffcd2b8040f2b2fafaea3d9f72", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/20756fec2f0108cb88e815941f1ffff88dc286fe", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/6 ... 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