CVE-2025-10933

Executive Summary

CVE-2025-10933 is an integer underflow vulnerability in the Silicon Labs Z-Wave Protocol Controller. This flaw can lead to out-of-bounds memory reads, potentially allowing an attacker to leak sensitive information or cause a denial of service. The vulnerability resides in the core protocol handling logic of the Z-Wave stack, which is used in smart home and IoT devices. No public exploit code or patch details are currently available, and the CVSS score is listed as 0.0, indicating incomplete assessment. The EPSS score is 0.0%, suggesting low exploitation activity at this time.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Unassigned)
• Attack Vector: Network (likely, based on Z-Wave protocol)
• Attack Complexity: Low (integer underflow is typically easy to trigger)
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: High (memory read can leak data)
• Integrity Impact: None
• Availability Impact: Low (potential crash)
• Threat Level: Medium (due to potential for information disclosure and lack of patch)

Deep Dive & Mechanics

The vulnerability is an integer underflow (CWE-191) in the Z-Wave Protocol Controller. Integer underflow occurs when a calculation produces a value smaller than the minimum representable integer, often leading to unexpected behavior. In this context, the underflow likely happens during packet length or offset calculations. When the controller processes a specially crafted Z-Wave frame, it may compute a negative length or offset, which is then used in a memory read operation. This results in reading memory outside the intended buffer, potentially exposing sensitive data such as encryption keys, device credentials, or other protocol state information.

The Z-Wave protocol operates in the sub-GHz ISM band and uses a mesh network topology. The Protocol Controller is a critical component that manages network formation, routing, and security. An attacker within radio range of a Z-Wave network could send a malicious frame to trigger the underflow. The impact is limited to memory reads, but repeated exploitation could lead to information leakage that aids further attacks.

Vulnerable vs. Patched Code

No patched code is available. The vulnerable code likely involves a subtraction operation on an unsigned integer without proper bounds checking. For example:

// Vulnerable pseudo-code
uint16_t length = packet_header.length - offset;
if (length > MAX_BUFFER_SIZE) {
    // error handling
}
memcpy(buffer, packet_data + offset, length); // underflow if offset > length

A patched version would include a check to ensure offset is less than or equal to length before subtraction, or use signed integers with proper validation.

Exploitation & Lab Setup

Red Team

1. Setup: Use a Z-Wave development kit (e.g., Silicon Labs Z-Wave 800 Series) and a software-defined radio (SDR) like the HackRF One to transmit raw Z-Wave frames.
2. Craft Payload: Create a Z-Wave frame with a manipulated length field that causes an integer underflow. For example, set the offset field to a value larger than the total packet length.
3. Transmit: Use a tool like libzwave or custom Python scripts with pyZwave to send the malicious frame to a target Z-Wave Protocol Controller.
4. Observe: Monitor the target device's memory output or crash logs to confirm out-of-bounds reads.

Blue Team

1. Detection: Monitor Z-Wave network traffic for anomalous frames with inconsistent length fields. Use a Z-Wave sniffer (e.g., Z-Wave PC Controller) to capture and analyze packets.
2. Mitigation: Apply input validation on all Z-Wave frame length fields. Ensure that offset values are always less than or equal to the total length before use.
3. Harden: Disable unnecessary Z-Wave services and segment IoT devices on a separate VLAN to limit exposure.

Indicators of Compromise (IOCs)

• Network: Z-Wave frames with length field values that cause underflow (e.g., offset > length)
• Host: Unexpected memory read errors or crashes in the Z-Wave Protocol Controller process
• Logs: Entries indicating "integer underflow" or "out-of-bounds read" in system logs
• File: Modified Z-Wave firmware binaries with patched length validation

Detection Engineering

YARA Rule

rule CVE_2025_10933_Z_Wave_Underflow {
    meta:
        description = "Detects potential integer underflow in Z-Wave Protocol Controller"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-10933"
    strings:
        $s1 = { 0F B7 45 ?? 66 2B 45 ?? } // movzx eax, word [ebp+var_X]; sub ax, word [ebp+var_Y]
        $s2 = { 66 2B C0 66 89 45 ?? } // sub ax, ax; mov word [ebp+var_X], ax
    condition:
        any of them
}

Sigma Rule

title: Z-Wave Protocol Controller Integer Underflow
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential exploitation of CVE-2025-10933 via anomalous Z-Wave frames
author: Valters IT
logsource:
    product: zeek
    service: zwave
detection:
    selection:
        zwave.frame.length|lt: 0
        zwave.frame.offset|gt: zwave.frame.length
    condition: selection
falsepositives:
    - Legitimate malformed frames from faulty devices
level: high

Suricata Rule

alert zwave any any -> any any (msg:"CVE-2025-10933 Z-Wave Integer Underflow Attempt"; content:"|00 00|"; offset:0; depth:2; byte_test:1,<,0,2; byte_test:1,>,2,3; sid:1000001; rev:1;)

Remediation & Mitigation

1. Patch: Apply firmware updates from Silicon Labs as soon as they become available. Monitor the Silicon Labs security advisory page for CVE-2025-10933.
2. Workaround: If patching is not possible, implement network-level filtering to drop Z-Wave frames with inconsistent length fields. Use a Z-Wave gateway with built-in anomaly detection.
3. Compensating Controls: Segment Z-Wave devices on a separate network and restrict physical access to the radio range. Use encryption and authentication features of Z-Wave S2 security.
4. Monitoring: Enable logging on Z-Wave Protocol Controllers and review logs for signs of exploitation. Deploy the provided detection rules.

Valters IT
DevSecOps & Cyber Threat Intelligence