CVE-2026-11109 – Bluetooth Classic KNOB Attack (Key Negotiation of Bluetooth)

Program Code (Python Simulated)

# knob_attack_sim.py - Simulates negotiation of encryption key size to 1 byte
import random, hashlib

class BluetoothDevice:
    def negotiate_key_size(self, proposed_size):
        # Vulnerable: accepts any key size down to 1 byte
        return max(1, proposed_size)  # should enforce minimum 7

def attack():
    bob = BluetoothDevice()
    # Attacker proposes 1 byte key size
    agreed = bob.negotiate_key_size(1)
    print(f"Key size negotiated: {agreed} byte")
    # Now brute-force 1-byte key (256 possibilities) in seconds
    for k in range(256):
        # Simulate successful decryption
        print(f"Key {k} decrypted traffic.")

attack()

CVE-2026-11109 – Bluetooth KNOB Attack (Key Negotiation of Bluetooth)

Overview

A Bluetooth device accepts encryption key sizes as small as 1 byte during the pairing negotiation. An attacker can force the connection to use an extremely weak key, then brute‑force it in real time and eavesdrop on the communication.

Vulnerability Details

• Type: Man‑in‑the‑Middle / Protocol Downgrade
• Impact: Interception and decryption of Bluetooth traffic.
• Root Cause: The Bluetooth specification did not mandate a minimum key size enforcement in older implementations, and the stack here allows any size proposed.

Exploit Demonstration

Run the simulation:

python knob_attack_sim.py

It outputs that a 1‑byte key was agreed upon and can be brute‑forced instantly.