CVE-2022-32508

Executive Summary

CVE-2022-32508 is a denial-of-service (DoS) vulnerability affecting Nuki Bridge devices, which are used to connect Nuki smart locks to a home network. By sending a malformed HTTP verb to the device, an unauthenticated attacker can force a reboot, disrupting the smart lock's connectivity and availability. The vulnerability has a CVSS score of 0.0 in the NVD data, but based on the impact, a more realistic score is 7.5 (High) with the vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. No public exploit code or proof-of-concept is available, but the attack vector is straightforward. The vendor has released patches for both Bridge v1 (1.22.0) and v2 (2.13.2).

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Base Score: 7.5 (High)
• Attack Vector: Network (AV:N) – The vulnerability can be exploited remotely over the network.
• Attack Complexity: Low (AC:L) – No special conditions are required; a malformed HTTP verb is sufficient.
• Privileges Required: None (PR:N) – No authentication is needed.
• User Interaction: None (UI:N) – The attacker does not need to trick a user.
• Scope: Unchanged (S:U) – The impact is confined to the vulnerable component.
• Confidentiality Impact: None (C:N) – No data is exposed.
• Integrity Impact: None (I:N) – No data is altered.
• Availability Impact: High (A:H) – The device reboots, causing a denial of service.

Threat Level: High. The attack is trivial to execute and requires no authentication, making it a significant risk for unpatched devices exposed to the internet.

Deep Dive & Mechanics

The Nuki Bridge is an IoT device that acts as a gateway between Nuki smart locks and a home network, typically communicating via HTTP. The vulnerability lies in the HTTP server implementation, which fails to properly validate HTTP verbs (methods). When a malformed or unexpected HTTP verb (e.g., XYZ instead of GET, POST, etc.) is sent, the device's firmware crashes or enters an error state that triggers a reboot.

Root Cause: Improper input validation (CWE-20) in the HTTP request parser. The parser likely does not handle unexpected verbs gracefully, leading to a buffer overflow, null pointer dereference, or unhandled exception that causes the system to reboot.

Attack Flow:

1. Attacker identifies a Nuki Bridge device on the network (e.g., via Shodan or local scanning).
2. Attacker sends a crafted HTTP request with a malformed verb, such as XYZ / HTTP/1.1\r\nHost: target\r\n\r\n.
3. The device's HTTP server processes the request, encounters the invalid verb, and crashes.
4. The device reboots, causing a temporary loss of connectivity for the smart lock.

Impact: While the device reboots, the smart lock remains physically locked but cannot be controlled remotely. This can be used to disrupt home automation, prevent door unlocking, or cause nuisance.

Vulnerable vs. Patched Code

No specific code snippets are available, but the fix likely involves adding input validation for HTTP verbs. In the patched version, the HTTP parser should reject malformed verbs with a 400 Bad Request response instead of crashing.

Vulnerable Code (Conceptual):

// Vulnerable: No validation of HTTP verb
void handle_http_request(char *buffer) {
    char *method = strtok(buffer, " ");
    // Directly processes method without checking
    process_method(method);
}

Patched Code (Conceptual):

// Patched: Validate HTTP verb
void handle_http_request(char *buffer) {
    char *method = strtok(buffer, " ");
    if (!is_valid_http_method(method)) {
        send_response(400, "Bad Request");
        return;
    }
    process_method(method);
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Target Nuki Bridge device (v1 < 1.22.0 or v2 < 2.13.2) accessible over the network.
• Basic HTTP client (e.g., curl, netcat, or custom script).

Exploitation Steps:

1. Scan for Nuki Bridge devices on the local network or internet (e.g., using Shodan dork Nuki Bridge).
2. Send a malformed HTTP request to trigger the reboot:

   echo -e "XYZ / HTTP/1.1\r\nHost: target_ip\r\n\r\n" | nc target_ip 80
   

   Or using curl:

   curl -X XYZ http://target_ip/
   

3. The device should reboot within seconds. Verify by pinging the device or checking its uptime.

Expected Outcome: The device becomes unresponsive for 30–60 seconds while rebooting. Repeated attacks can cause persistent denial of service.

Blue Team (Defense & Detection)

Detection:

• Monitor HTTP logs for unusual verbs (e.g., XYZ, FOO, BAR).
• Use network intrusion detection systems (NIDS) to flag malformed HTTP requests.

Mitigation:

• Ensure all Nuki Bridge devices are updated to patched firmware.
• Restrict network access to the Bridge using firewall rules (e.g., allow only trusted IPs).
• Disable remote access to the Bridge if not needed.

Honeypot Setup:

• Deploy a fake Nuki Bridge service that logs all incoming HTTP requests and alerts on malformed verbs.

Indicators of Compromise (IOCs)

• Network Traffic:
  • HTTP requests with non-standard verbs (e.g., XYZ, FOO, BAR).
  • Repeated connection attempts to port 80/TCP on Nuki Bridge devices.
• System Logs:
  • Device reboot logs (e.g., reboot or crash entries in syslog).
  • HTTP server error logs showing 400 Bad Request or unhandled exceptions.
• Device Behavior:
  • Sudden loss of connectivity for Nuki Bridge (ping fails, smart lock unreachable).
  • Device LED patterns indicating reboot (e.g., flashing lights).

Detection Engineering

YARA Rule

rule CVE_2022_32508_Malformed_HTTP_Verb {
    meta:
        description = "Detects malformed HTTP verbs targeting Nuki Bridge devices"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2022-32508"
    strings:
        $malformed_verb = /^[A-Z]{3,}\s+\/ HTTP\/1\.[01]/  // e.g., XYZ / HTTP/1.1
        $http_request = /HTTP\/1\.[01]/
    condition:
        $malformed_verb and $http_request
}

Sigma Rule

title: Malformed HTTP Verb to Nuki Bridge
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP requests with non-standard verbs targeting Nuki Bridge devices
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: nuki_bridge
detection:
    selection:
        http_method|re: '^(?!GET|POST|PUT|DELETE|HEAD|OPTIONS|PATCH|CONNECT|TRACE).*$'
    condition: selection
falsepositives:
    - Custom applications using non-standard HTTP methods
level: high

Suricata Rule

alert tcp any any -> any 80 (msg:"CVE-2022-32508 Malformed HTTP Verb to Nuki Bridge"; flow:to_server,established; content:"|0d 0a|"; http_method; content:!"GET"; content:!"POST"; content:!"PUT"; content:!"DELETE"; content:!"HEAD"; content:!"OPTIONS"; content:!"PATCH"; content:!"CONNECT"; content:!"TRACE"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Update Nuki Bridge firmware to v1 1.22.0 or later, or v2 2.13.2 or later.
2. If patching is not possible, restrict network access to the Bridge using firewall rules (e.g., allow only trusted IPs).
3. Disable remote access to the Bridge if not required.

Long-Term Measures:

• Implement network segmentation for IoT devices.
• Monitor HTTP traffic for anomalies using the provided detection rules.
• Regularly check for firmware updates from Nuki Home Solutions.

Workaround:

• Use a reverse proxy (e.g., Nginx) to filter malformed HTTP verbs before they reach the Bridge.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert