CVE-2024-6352

Executive Summary

CVE-2024-6352 is a buffer overflow vulnerability in the Application Support (APS) layer of the Ember ZNet stack, a widely used Zigbee protocol stack for IoT devices. A malformed packet can trigger a buffer overflow, leading to an assertion failure and subsequent denial of service (DoS). The vulnerability has a CVSS score of 4.3 (Medium) and an EPSS score of 0.0%, indicating low exploitation likelihood in the wild. No public exploit code or patch is currently available. The affected component is the APS layer, which handles message fragmentation and reassembly in Zigbee networks.

Note: This vulnerability is not related to WordPress, Apache, or Nginx. It is a firmware-level issue in the Ember ZNet stack used in embedded Zigbee devices.

Supply Chain & Package Security

This vulnerability is not in a typical software package manager (NPM, PyPI, Go, Ruby). It affects a proprietary firmware stack (Ember ZNet) used in IoT/embedded devices. Supply chain risk is elevated because:

• No patch is available from the vendor.
• Devices using this stack may be deployed in critical infrastructure (smart buildings, industrial IoT).
• Firmware updates for embedded devices are often delayed or not applied.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
• Base Score: 4.3 (Medium)
• Attack Vector: Network (AV:N) – The vulnerability can be triggered remotely over a Zigbee network.
• Attack Complexity: Low (AC:L) – No special conditions required; a malformed packet is sufficient.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – The exploit does not affect other components.
• Confidentiality Impact: None (C:N) – No data leakage.
• Integrity Impact: None (I:N) – No data modification.
• Availability Impact: Low (A:L) – The device may crash or restart, causing temporary DoS.

Threat Level: Medium. While the CVSS score is moderate, the lack of a patch and the potential for widespread IoT disruption elevate the risk for organizations using Ember ZNet-based devices.

Deep Dive & Mechanics

The Ember ZNet stack implements the Zigbee protocol, where the APS layer is responsible for message fragmentation, reassembly, and end-to-end acknowledgment. The vulnerability lies in how the APS layer processes incoming packets. A malformed packet—specifically one with an invalid length field or fragmented data—can cause a buffer overflow when the stack attempts to copy data into a fixed-size buffer without proper bounds checking.

Technical Flow:

1. An attacker sends a crafted Zigbee APS packet to a vulnerable device.
2. The APS layer receives the packet and attempts to parse it.
3. Due to insufficient validation of packet length or fragment offsets, the stack copies data beyond the allocated buffer.
4. The overflow corrupts adjacent memory, eventually triggering an assertion (assert) in the stack.
5. The assertion causes the device to crash or enter an infinite loop, resulting in denial of service.

Root Cause: Lack of input validation in the APS layer’s packet parsing routine. The buffer size is fixed, but the packet length is not checked against it before copying.

Vulnerable vs. Patched Code

Since no patch is available, a hypothetical fix would involve adding bounds checking before memory copy operations. Below is a simplified example of the vulnerable pattern and a patched version.

Vulnerable Code (C-like pseudocode):

void aps_process_packet(uint8_t *packet, uint16_t length) {
    uint8_t buffer[256];
    // No length check
    memcpy(buffer, packet, length);
    // ... further processing
}

Patched Code (Hypothetical):

void aps_process_packet(uint8_t *packet, uint16_t length) {
    uint8_t buffer[256];
    if (length > sizeof(buffer)) {
        // Reject malformed packet
        return;
    }
    memcpy(buffer, packet, length);
    // ... further processing
}

Exploitation & Lab Setup

Red Team (Exploitation)

No public exploit code is available. However, a proof-of-concept can be developed using a Zigbee sniffer and a custom packet injector (e.g., using a CC2531 dongle and KillerBee framework).

Lab Setup:

• Hardware: TI CC2531 USB dongle, vulnerable Ember ZNet device (e.g., a smart plug).
• Software: KillerBee, Scapy, or a custom Python script using zboss library.

Steps:

1. Capture a legitimate APS packet using a sniffer.
2. Modify the packet to have an oversized length field or invalid fragment offset.
3. Transmit the malformed packet to the target device.
4. Observe device crash or reset.

Example Python script (conceptual):

from killerbee import *
import struct

# Craft malformed APS packet
aps_payload = b'\x00' * 300  # Exceeds buffer size
packet = struct.pack('<H', len(aps_payload)) + aps_payload

# Send over Zigbee
kb = KillerBee()
kb.set_channel(11)
kb.inject(packet)

Blue Team (Defense)

Detection:

• Monitor Zigbee network for anomalous packets with excessive length or invalid fragment sequences.
• Use network intrusion detection systems (NIDS) that support Zigbee protocol analysis (e.g., Wireshark with Zigbee dissector).

Mitigation:

• Isolate vulnerable devices on a separate Zigbee network.
• Apply firmware updates if/when available.
• Use Zigbee firewalls or gateways that validate APS layer packets.

Indicators of Compromise (IOCs)

• Network IOCs:

  • Zigbee packets with APS payload length > 256 bytes.
  • Repeated APS fragment packets with invalid offset values.
  • Device logs showing assert failures in APS layer.

• Host IOCs:

  • Unexpected device reboots or crashes.
  • Firmware crash dumps referencing APS buffer overflow.

• File IOCs:

  • None (firmware-level vulnerability).

Detection Engineering

YARA Rule

rule CVE_2024_6352_Ember_ZNet_APS_Overflow {
    meta:
        description = "Detects malformed APS packets targeting Ember ZNet stack"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2024-6352"
    strings:
        $aps_header = { 00 00 00 00 }  // Example APS header pattern
        $overflow_len = { FF 00 }      // Length field > 256
    condition:
        $aps_header and $overflow_len
}

Sigma Rule

title: CVE-2024-6352 Ember ZNet APS Buffer Overflow
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects malformed Zigbee APS packets that may trigger buffer overflow
author: Valters IT
date: 2025-04-10
logsource:
    category: network
    product: zigbee
detection:
    selection:
        aps_payload_length: >256
    condition: selection
falsepositives:
    - Legitimate large firmware updates (rare)
level: high

Suricata Rule

alert zigbee any any -> any any (msg:"CVE-2024-6352 Ember ZNet APS Buffer Overflow Attempt"; flow:to_server; content:"|00 00 00 00|"; offset:0; depth:4; byte_test:2,>,256,4,relative; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate vulnerable devices on a separate Zigbee network or VLAN.
2. Monitor network traffic for anomalous APS packets using the provided detection rules.
3. Contact vendor (Ember/Silicon Labs) for patch status and workarounds.

Long-term Fixes:

• Apply firmware updates when released by the vendor.
• Implement input validation in custom Zigbee applications using the Ember stack.
• Consider replacing devices with those using a patched stack.

Workarounds:

• Disable APS fragmentation if not required (may impact functionality).
• Use Zigbee gateways that perform deep packet inspection.

Valters IT Signature This report was generated by Valters IT Cyber Threat Intelligence Division. For questions, contact cti@valters-it.com.