CVE-2025-31700

Executive Summary

CVE-2025-31700 is a high-severity buffer overflow vulnerability affecting Dahua products. An unauthenticated attacker can exploit this flaw by sending specially crafted malicious packets to the target device. Successful exploitation can lead to service disruption (Denial of Service) or, in some cases, Remote Code Execution (RCE). While some devices may have ASLR enabled, reducing the likelihood of RCE, the DoS risk remains significant. The vulnerability is currently unpatched, and no public proof-of-concept (PoC) or exploit code is available. The EPSS score is 0.0%, indicating low exploitation activity in the wild at this time.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level vulnerability in Dahua hardware products (DVRs, NVRs, IP cameras). Organizations using Dahua devices should treat this as a critical supply chain risk, as the vendor has not yet provided a patch.

CVSS Breakdown & Threat Level

• CVSS Score: 8.1 (High)
• Attack Vector (AV): Network (N) - Exploitable remotely.
• Attack Complexity (AC): Low (L) - No special conditions required.
• Privileges Required (PR): None (N) - No authentication needed.
• User Interaction (UI): None (N) - No user action required.
• Scope (S): Unchanged (U) - The exploit does not affect other components.
• Confidentiality (C): None (N) - No data exposure.
• Integrity (I): None (N) - No data modification.
• Availability (A): High (H) - Complete loss of availability (DoS).

Threat Level: High. The low attack complexity and lack of required privileges make this a serious threat, especially for unpatched devices exposed to the internet.

Deep Dive & Mechanics

The vulnerability is a classic buffer overflow (CWE-120). The Dahua device's network service fails to properly validate the length of incoming data before copying it into a fixed-size buffer. An attacker can send a packet that exceeds the buffer's capacity, overwriting adjacent memory regions.

Technical Flow:

1. The Dahua device listens on a network port (e.g., TCP 37777 or UDP 5000) for management or streaming protocols.
2. A specific field in the packet header or payload is read without bounds checking.
3. The attacker crafts a packet where this field contains data larger than the allocated buffer.
4. The overflow corrupts the stack or heap, potentially overwriting the return address or function pointers.
5. If ASLR is disabled or bypassed, the attacker can redirect execution to shellcode, achieving RCE.
6. Even without RCE, the overflow can cause a crash (DoS) by corrupting critical data structures.

Affected Components: Likely the NetClient or RtspServer processes in Dahua firmware. The exact vulnerable function is not publicly known.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, a typical vulnerable code pattern in C/C++ would be:

Vulnerable Code (Hypothetical):

void process_packet(char *packet) {
    char buffer[256];
    // No bounds check
    strcpy(buffer, packet);
}

Patched Code (Hypothetical):

void process_packet(char *packet, size_t packet_len) {
    char buffer[256];
    if (packet_len >= sizeof(buffer)) {
        // Reject oversized packet
        return;
    }
    strncpy(buffer, packet, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
}

The fix would involve adding input validation and using safe string functions like strncpy or snprintf.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A vulnerable Dahua device (e.g., Dahua DVR/NVR with firmware version < unknown).
• Network access to the device.
• Python 3 with socket library.

Exploit Concept (No Public PoC): Since no public exploit exists, the following is a conceptual Python script to trigger a DoS by sending an oversized packet.

import socket

target_ip = "192.168.1.100"
target_port = 37777  # Common Dahua port

# Craft a malicious packet with a large payload
payload = b"A" * 4096  # Overflow buffer

try:
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.settimeout(5)
    sock.connect((target_ip, target_port))
    sock.send(payload)
    print("[+] Payload sent. Device may crash.")
except Exception as e:
    print(f"[-] Error: {e}")
finally:
    sock.close()

Note: This is for educational purposes only. Unauthorized testing is illegal.

Blue Team (Defensive)

Detection:

• Monitor for unusually large packets on ports 37777, 5000, or 80/443 (if web interface is exposed).
• Use network intrusion detection systems (NIDS) to alert on buffer overflow signatures.
• Enable logging on Dahua devices and review for crash logs or unexpected reboots.

Mitigation:

• Isolate Dahua devices on a separate VLAN with strict firewall rules.
• Disable remote access if not required.
• Apply virtual patching via WAF or IPS if available.

Indicators of Compromise (IOCs)

• Network IOCs:

  • Packets with payloads exceeding 1024 bytes on TCP port 37777 or UDP port 5000.
  • Repeated connection attempts from a single IP to multiple Dahua devices.
  • Traffic containing long strings of repeating characters (e.g., "AAAA...").

• Host IOCs (on the device):

  • Unexpected reboots or crashes.
  • Log entries indicating "buffer overflow" or "segmentation fault".
  • High CPU usage or memory exhaustion.

• File IOCs:

  • No specific file hashes available.

Detection Engineering

YARA Rule

rule CVE_2025_31700_Dahua_BufferOverflow {
    meta:
        description = "Detects network traffic targeting Dahua buffer overflow vulnerability"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-31700"
    strings:
        $s1 = "Dahua" ascii wide nocase
        $s2 = "RTSP" ascii wide nocase
        $s3 = { 41 41 41 41 } // "AAAA" pattern
    condition:
        $s1 and $s2 and #s3 > 10
}

Sigma Rule

title: Dahua Buffer Overflow Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects network packets with excessive length targeting Dahua devices
author: Valters IT
date: 2025/04/10
logsource:
    category: network_connection
    product: suricata
detection:
    selection:
        dest_port:
            - 37777
            - 5000
        payload_length: '>1024'
    condition: selection
falsepositives:
    - Legitimate large firmware updates (rare)
level: high

Suricata Rule

alert tcp $EXTERNAL_NET any -> $HOME_NET 37777 (msg:"CVE-2025-31700 Dahua Buffer Overflow Attempt"; flow:to_server,established; content:"|41 41 41 41|"; depth:1024; threshold:type both, track by_src, count 1, seconds 60; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Network Segmentation: Place all Dahua devices on a dedicated VLAN with strict ACLs. Do not expose them directly to the internet.
2. Firewall Rules: Block inbound traffic to ports 37777, 5000, and 80/443 from untrusted networks.
3. Monitor: Enable logging and monitor for crash events or unusual network traffic.

Long-Term Actions:

1. Vendor Patch: Await an official firmware update from Dahua. Subscribe to their security advisory mailing list.
2. Virtual Patching: If using a WAF or IPS, create custom rules to block oversized packets.
3. Device Replacement: If the vendor does not patch within a reasonable timeframe, consider replacing the devices with alternatives from vendors with better security practices.

Workaround: Disable the vulnerable service if not needed. For example, if RTSP streaming is not required, disable it in the device settings.

Valters IT