CVE-2025-50610

Executive Summary

CVE-2025-50610 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_00476598 function within the cgitest.cgi binary. An attacker can trigger a Denial of Service (DoS) by controlling the wl_base_set_5g parameter in the HTTP payload, causing the program to crash. No patch is currently available from the vendor, 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).

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating that no official CVSS vector has been assigned by NVD. However, based on the nature of the vulnerability (buffer overflow leading to DoS), a reasonable estimated vector would be:

• Attack Vector (AV): Network (AV:N) – The vulnerability is exploitable over the network via HTTP requests to the cgitest.cgi endpoint.
• Attack Complexity (AC): Low (AC:L) – No special conditions are required; the attacker simply sends a crafted payload.
• Privileges Required (PR): None (PR:N) – No authentication is needed to access the vulnerable CGI endpoint.
• User Interaction (UI): None (UI:N) – The attack does not require any user action.
• Scope (S): Unchanged (S:U) – The vulnerability affects only the router's availability.
• Confidentiality (C): None (C:N) – No data exposure.
• Integrity (I): None (I:N) – No data modification.
• Availability (A): High (A:H) – The crash leads to 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 – The vulnerability is easily exploitable remotely without authentication, and while it only causes a DoS, it can disrupt network operations for all users behind the affected router.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the FUN_00476598 function of the cgitest.cgi CGI binary. This function is responsible for processing the wl_base_set_5g parameter from HTTP POST requests. The parameter is copied into a fixed-size stack buffer without proper bounds checking. By providing an overly long value for wl_base_set_5g, an attacker can overflow the buffer, overwriting the return address and other critical stack data. This causes the program to crash, resulting in a Denial of Service.

The cgitest.cgi endpoint is typically used for diagnostic or configuration purposes and is accessible without authentication on the Netis WF2880 router. The overflow occurs during the strcpy or similar unsafe string copy operation within the function. Since no exploit code has been published, the exact offset to control the instruction pointer is unknown, but the crash is reliably triggered by a long string.

Vulnerable vs. Patched Code

Vulnerable Code (Netis WF2880 v2.1.40207): The vulnerable function FUN_00476598 uses an unsafe string copy (likely strcpy or sprintf) to copy the wl_base_set_5g parameter into a stack buffer of limited size. No length validation is performed.

// Pseudocode of vulnerable function
void FUN_00476598(char *input) {
    char buffer[256];
    strcpy(buffer, input); // Unsafe: no bounds check
    // ... further processing
}

Patched Code (Hypothetical): A patched version would use safe string copy functions with length limits, such as strncpy or snprintf, and validate the input length before copying.

// Pseudocode of patched function
void FUN_00476598(char *input) {
    char buffer[256];
    strncpy(buffer, input, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... further processing
}

Since no official patch has been released, users are advised to apply workarounds such as disabling the cgitest.cgi endpoint or restricting network access to the router's management interface.

Exploitation & Lab Setup

Red Team (Exploitation)

Lab Setup:

• Target: Netis WF2880 router with firmware v2.1.40207
• Attacker: Kali Linux machine on the same network
• Tool: curl or custom Python script

Exploitation Steps:

1. Identify the router's IP address (e.g., 192.168.1.1).
2. Send a crafted HTTP POST request with an overly long wl_base_set_5g parameter.

curl -X POST http://192.168.1.1/cgitest.cgi \
  -d "wl_base_set_5g=$(python3 -c 'print("A"*1000)')"

3. The router's CGI process crashes, causing the web interface to become unresponsive. The router may reboot or require a power cycle to recover.

Expected Outcome: The router becomes unavailable for legitimate users, achieving a Denial of Service.

Blue Team (Defense & Detection)

Detection:

• Monitor HTTP POST requests to /cgitest.cgi with unusually long parameter values.
• Use network intrusion detection systems (NIDS) to alert on oversized payloads.

Mitigation:

• Block access to the router's management interface from untrusted networks.
• Disable the cgitest.cgi endpoint if not required.
• Apply vendor firmware updates when available.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP POST requests to /cgitest.cgi with wl_base_set_5g parameter length exceeding 256 bytes.
  • Source IP addresses repeatedly sending large payloads to the router's management interface.
• System IOCs:
  • Router web interface becomes unresponsive.
  • Router logs (if accessible) showing crashes in the cgitest.cgi process.
  • Unexpected reboots of the router.

Detection Engineering

YARA Rule

rule CVE_2025_50610_Netis_WF2880_BufferOverflow {
    meta:
        description = "Detects exploit attempts for CVE-2025-50610 targeting Netis WF2880"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-50610"
    strings:
        $payload = /wl_base_set_5g=[A-Za-z0-9%]{257,}/ nocase
    condition:
        $payload
}

Sigma Rule

title: CVE-2025-50610 Netis WF2880 Buffer Overflow Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP POST requests with an overly long wl_base_set_5g parameter targeting cgitest.cgi
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/cgitest.cgi'
        cs-uri-query|contains: 'wl_base_set_5g='
        cs-uri-query|length: >= 300
    condition: selection
falsepositives:
    - Legitimate long configuration values (unlikely)
level: high

Suricata Rule

alert http any any -> $HOME_NET any (msg:"CVE-2025-50610 Netis WF2880 Buffer Overflow Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/cgitest.cgi"; http_uri; content:"wl_base_set_5g="; http_client_body; pcre:"/wl_base_set_5g=[A-Za-z0-9%]{257,}/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Remote Management: Ensure the router's web interface is not accessible from the internet. Use firewall rules to restrict access to trusted local IPs only.
2. Disable cgitest.cgi: If possible, block or remove the cgitest.cgi endpoint. This can be done by modifying the router's configuration or using a reverse proxy to filter requests.
3. Monitor Logs: Enable logging on the router and monitor for unusual HTTP requests to /cgitest.cgi.

Long-Term Actions:

1. Vendor Patch: Contact Netis support and request a firmware update that fixes the buffer overflow. Check the vendor's website periodically for updates.
2. Replace Router: If no patch is forthcoming, consider replacing the Netis WF2880 with a more secure router model that receives regular security updates.
3. Network Segmentation: Place the router in a separate VLAN and limit its exposure to critical network segments.

Workarounds:

• Use a web application firewall (WAF) to block requests with overly long wl_base_set_5g parameters.
• Implement rate limiting on the router's management interface to slow down brute-force or DoS attempts.

Valters IT
Securing Digital Frontiers