CVE-2022-32502

Executive Summary

CVE-2022-32502 is a critical buffer overflow vulnerability discovered in Nuki Home Solutions smart lock bridge devices. The flaw resides in the encrypted token parsing logic of the HTTP service, allowing an unauthenticated, remote attacker to trigger a buffer overflow and achieve remote code execution (RCE). This affects Nuki Bridge v1 (before 1.22.0) and v2 (before 2.13.2). The vulnerability is particularly dangerous as it can be exploited over the network without authentication, potentially granting full control of the bridge device. No public proof-of-concept (PoC) or exploit code has been released at this time, and the EPSS score is 0.0%, indicating low exploitation activity in the wild. However, given the nature of the vulnerability and the device's role in home security, immediate patching is strongly recommended.

Supply Chain & Package Security

This vulnerability is not related to any open-source package manager (NPM, PyPI, Go, Ruby). It is a firmware-level issue in proprietary Nuki hardware. The supply chain risk is limited to the physical device and its firmware update mechanism.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0 in the NVD data, which is likely a placeholder. Based on the description (unauthenticated remote code execution), a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N)
• Attack Complexity (AC): Low (L)
• Privileges Required (PR): None (N)
• User Interaction (UI): None (N)
• Scope (S): Unchanged (U)
• Confidentiality (C): High (H)
• Integrity (I): High (H)
• Availability (A): High (H)

Estimated CVSS Score: 9.8 (Critical)

Threat Level: Critical. The vulnerability allows complete compromise of the bridge device, which can be used to control smart locks, exfiltrate data, or pivot to other devices on the local network.

Deep Dive & Mechanics

The vulnerability is a classic buffer overflow in the encrypted token parsing logic of the HTTP service running on Nuki Bridge devices. The HTTP service likely handles encrypted tokens for authentication or command validation. When parsing these tokens, the software fails to properly validate the length of the input before copying it into a fixed-size buffer. An attacker can send a specially crafted HTTP request containing an overly long encrypted token, causing the buffer to overflow and overwrite adjacent memory regions. This can corrupt the program's state and, with careful crafting, allow the attacker to redirect execution flow to arbitrary code (shellcode).

The attack is performed over the network, typically on the local network where the bridge is connected, but could also be exploited from the internet if the device is exposed. The encrypted nature of the token may require the attacker to understand the encryption scheme or simply send a long string that triggers the overflow before decryption is fully validated.

Vulnerable vs. Patched Code

Since no source code is publicly available, the following is a hypothetical representation of the vulnerable and patched code.

Vulnerable Code (C-like pseudocode):

void parse_token(char *encrypted_token) {
    char buffer[256];
    // Vulnerable: no bounds checking
    strcpy(buffer, encrypted_token);
    // ... further processing
}

Patched Code (C-like pseudocode):

void parse_token(char *encrypted_token) {
    char buffer[256];
    // Patched: use strncpy with length limit
    strncpy(buffer, encrypted_token, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... further processing
}

The fix involves replacing strcpy with strncpy (or similar safe functions) to ensure the input does not exceed the buffer size.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Obtain a Nuki Bridge v1 or v2 device (firmware version < 1.22.0 or < 2.13.2).
2. Connect the bridge to a local network with a controlled attacker machine (e.g., Kali Linux).
3. Identify the bridge's IP address (e.g., via Nmap scan).

Exploitation Steps:

1. Craft a malicious HTTP request with an overly long encrypted token in the appropriate header or parameter.
2. Use a tool like curl or a custom Python script to send the request.
3. The buffer overflow will overwrite the return address or function pointer.
4. Redirect execution to shellcode (e.g., a reverse shell payload).
5. Gain a shell on the bridge device.

Example Python exploit skeleton:

import socket

target_ip = "192.168.1.100"
target_port = 80

# Craft payload: overflow buffer + overwrite return address + shellcode
payload = b"A" * 256  # Fill buffer
payload += b"BBBB"    # Overwrite saved EBP
payload += b"CCCC"    # Overwrite return address (to be replaced with shellcode address)
payload += b"\x90" * 100  # NOP sled
payload += shellcode  # Reverse shell shellcode

http_request = f"POST / HTTP/1.1\r\nHost: {target_ip}\r\nContent-Length: {len(payload)}\r\n\r\n".encode() + payload

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, target_port))
sock.send(http_request)
sock.close()

Note: No public exploit code is available. The above is a generic example.

Blue Team (Defensive)

Detection & Response:

1. Monitor for unusually long HTTP requests to the bridge, especially those with large token fields.
2. Implement network segmentation to isolate IoT devices like the bridge from critical systems.
3. Enable logging on the bridge (if supported) and forward logs to a SIEM.
4. Use intrusion detection systems (IDS) to alert on buffer overflow patterns.
5. Apply the vendor patch immediately.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests with Content-Length exceeding normal token sizes (e.g., > 1024 bytes).
  • Repeated connection attempts to the bridge from unknown IPs.
  • Outbound connections from the bridge to unusual IPs/ports (e.g., reverse shell).
• Host IOCs:
  • Unexpected processes running on the bridge (e.g., /bin/sh).
  • Modified firmware or configuration files.
  • High CPU or memory usage due to exploitation.
• File IOCs:
  • Presence of shellcode or malicious binaries in /tmp or other writable directories.

Detection Engineering

YARA Rule

rule CVE_2022_32502_Nuki_Bridge_Buffer_Overflow {
    meta:
        description = "Detects exploit attempts for CVE-2022-32502 targeting Nuki Bridge"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2022-32502"
    strings:
        $http_method = "POST" ascii wide nocase
        $token_field = "token" ascii wide nocase
        $long_string = /[A-Za-z0-9+\/=]{512,}/  // Base64-like long token
    condition:
        $http_method and $token_field and $long_string
}

Sigma Rule

title: CVE-2022-32502 Nuki Bridge Buffer Overflow Attempt
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP requests with abnormally long token fields targeting Nuki Bridge devices
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: nuki_bridge
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'token'
        sc-bytes|>=: 1024
    condition: selection
falsepositives:
    - Legitimate large tokens (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2022-32502 Nuki Bridge Buffer Overflow Attempt"; flow:to_server; content:"POST"; http_method; content:"token"; http_client_body; byte_test:1,>,1024,0,relative; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Patch: Update Nuki Bridge v1 to firmware version 1.22.0 or later, and v2 to 2.13.2 or later. This is the only definitive fix.
2. Network Segmentation: Place the bridge on a separate VLAN with restricted access to the internet and other internal networks.
3. Firewall Rules: Block inbound HTTP traffic to the bridge from untrusted networks (e.g., the internet). Only allow necessary traffic from trusted management hosts.
4. Monitor: Enable logging and monitor for suspicious HTTP requests as described in the Detection Engineering section.

Long-Term Measures:

• Implement a vulnerability management program for IoT devices.
• Regularly check for firmware updates from Nuki.
• Consider using a web application firewall (WAF) to filter malicious requests.

Valters IT
Securing Your Digital Frontier