CVE-2024-39947

Executive Summary

CVE-2024-39947 is a denial-of-service (DoS) vulnerability affecting Dahua products. An attacker who has obtained valid low-privileged credentials (username and password) can send a specially crafted data packet to a vulnerable interface, causing the target device to crash. The vulnerability has a CVSS score of 6.5 (Medium) and is currently unpatched. No public proof-of-concept (PoC) code or exploit is available at this time. The attack requires prior authentication, reducing the attack surface but still posing a significant risk to exposed devices.

Supply Chain & Package Security

This vulnerability is not related to any open-source package ecosystem (NPM, PyPI, Go, Ruby). It affects proprietary Dahua firmware and hardware.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Attack Vector (AV): Network (N)
• Attack Complexity (AC): Low (L)
• Privileges Required (PR): Low (L) – attacker needs a valid user account.
• User Interaction (UI): None (N)
• Scope (S): Unchanged (U)
• Confidentiality (C): None (N)
• Integrity (I): None (N)
• Availability (A): High (H)

Threat Level: Medium. The requirement for valid credentials reduces the likelihood of widespread exploitation, but the impact on availability is high. Once an attacker has a foothold, they can easily disrupt operations.

Deep Dive & Mechanics

The vulnerability lies in an unspecified interface within Dahua devices. The exact endpoint or protocol is not publicly documented. The attack works as follows:

1. Authentication: The attacker first obtains valid credentials for a low-privileged user (e.g., via phishing, credential stuffing, or default credentials).
2. Crafted Packet: The attacker sends a maliciously crafted data packet to the vulnerable interface. The packet likely contains malformed data, an unexpected data type, or an out-of-bounds value that the device's input validation fails to handle.
3. Crash: The device's firmware processes the packet, leading to a memory corruption, buffer overflow, or null pointer dereference, causing the device to crash and become unresponsive.

The vulnerability is classified as CWE-20 (Improper Input Validation), indicating that the device does not properly validate the structure or content of incoming data before processing it.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, the vulnerability likely exists in a function that parses network packets. A vulnerable implementation might look like:

// Vulnerable pseudo-code
void process_packet(char *data, int len) {
    char buffer[1024];
    // No bounds checking
    memcpy(buffer, data, len);
    // Process buffer...
}

A patched version would include proper input validation and bounds checking:

// Patched pseudo-code
void process_packet(char *data, int len) {
    char buffer[1024];
    if (len > sizeof(buffer)) {
        // Reject oversized packet
        return;
    }
    memcpy(buffer, data, len);
    // Process buffer...
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• A Dahua device (e.g., DVR, NVR, IP camera) with a known vulnerable firmware version.
• Valid credentials for a low-privileged user (e.g., user / pass).

Steps:

1. Identify the target: Use Shodan or a network scan to find Dahua devices.
2. Authenticate: Log in to the device's web interface or API using the obtained credentials.
3. Craft the payload: Since no public PoC exists, you would need to reverse-engineer the device's firmware to identify the vulnerable interface and craft a malformed packet. This typically involves:
   • Analyzing the firmware binary (e.g., using binwalk, Ghidra).
   • Identifying network service handlers.
   • Fuzzing the interface with malformed data.
4. Send the packet: Use a tool like netcat, Python, or Burp Suite to send the crafted packet to the vulnerable endpoint.
5. Observe the crash: The device should become unresponsive. A physical reboot may be required to restore functionality.

Example Python script (hypothetical):

import socket

target_ip = "192.168.1.100"
target_port = 80  # Example port
username = "user"
password = "pass"

# Craft a malformed packet (hypothetical)
payload = b"\x00" * 1000  # Oversized data

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, target_port))
# Authenticate and send payload
sock.send(payload)
sock.close()

Blue Team

Detection:

• Monitor for unusual network traffic to Dahua devices, especially malformed or oversized packets.
• Look for repeated authentication attempts followed by a sudden spike in traffic to a single endpoint.
• Use the Sigma and Suricata rules provided in the Detection Engineering section.

Response:

• Isolate affected devices from the network.
• Reboot the device to restore functionality.
• Change all credentials immediately.
• Apply network segmentation to limit exposure.
• Monitor for any signs of persistence or lateral movement.

Indicators of Compromise (IOCs)

• Network:
  • Unusually large or malformed packets sent to Dahua device ports (e.g., 80, 443, 37777, 554).
  • Repeated failed login attempts followed by a crash event.
• Host:
  • Device logs showing unexpected crashes or reboots.
  • Memory dumps or core files on the device (if accessible).
• File:
  • No specific file-based IOCs are known.

Detection Engineering

YARA Rule

rule CVE_2024_39947_Dahua_DoS {
    meta:
        description = "Detects potential exploit attempts for CVE-2024-39947 targeting Dahua devices"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-39947"
    strings:
        $s1 = "Dahua" ascii wide nocase
        $s2 = "DVR" ascii wide nocase
        $s3 = "NVR" ascii wide nocase
        $s4 = "IPC" ascii wide nocase
        $malformed1 = { 00 00 00 00 00 00 00 00 } // Example pattern
    condition:
        any of ($s*) and #malformed1 > 10
}

Sigma Rule

title: CVE-2024-39947 Dahua DoS Exploit Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects network traffic patterns indicative of an exploit attempt for CVE-2024-39947
author: Valters IT
date: 2024/01/01
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-39947
logsource:
    category: network
    product: suricata
detection:
    selection:
        dest_port:
            - 80
            - 443
            - 37777
            - 554
        payload_length: '> 1024'
    condition: selection
falsepositives:
    - Legitimate large data transfers (e.g., video streaming)
level: high

Suricata Rule

alert tcp $EXTERNAL_NET any -> $HOME_NET [80,443,37777,554] (msg:"CVE-2024-39947 Dahua DoS Exploit Attempt"; flow:to_server,established; content:"|00 00 00 00|"; depth:4; byte_test:4,>,1024,0,relative; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Change Default Credentials: Ensure all Dahua devices use strong, unique passwords.
2. Network Segmentation: Place Dahua devices on a separate VLAN with strict firewall rules. Do not expose them directly to the internet.
3. Monitor Logs: Enable and monitor device logs for signs of crashes or unusual activity.
4. Disable Unused Services: Turn off any unnecessary network services on the device.

Long-Term Actions:

1. Vendor Patch: Monitor Dahua's official website for a firmware update that addresses this vulnerability. Apply it as soon as it becomes available.
2. Replace Devices: If a patch is not released, consider replacing affected devices with alternatives from vendors with a better security track record.
3. Implement IDS/IPS: Deploy the Suricata rule provided above to detect and block exploit attempts.

Workaround:

• If the vulnerable interface is known, block access to it via firewall rules. However, since the exact interface is unknown, this may not be feasible.

Valters IT