CVE-2025-4140: Netgear EX6120 Buffer Overflow Vulnerability

CVE-2025-4140 Overview

A critical buffer overflow vulnerability has been identified in the Netgear EX6120 Wi-Fi range extender running firmware version 1.0.3.94. The vulnerability exists in the function sub_30394, where improper handling of the host argument allows an attacker to trigger a buffer overflow condition. This flaw can be exploited remotely by an authenticated attacker to potentially achieve arbitrary code execution on the affected device.

Critical Impact

Remote attackers with low-level privileges can exploit this buffer overflow to compromise the integrity, confidentiality, and availability of the Netgear EX6120 device, potentially gaining complete control over the network extender.

Affected Products

• Netgear EX6120 Firmware version 1.0.3.94
• Netgear EX6120 Hardware

Discovery Timeline

• April 30, 2025 - CVE-2025-4140 published to NVD
• May 12, 2025 - Last updated in NVD database

Technical Details for CVE-2025-4140

Vulnerability Analysis

This buffer overflow vulnerability resides within the sub_30394 function of the Netgear EX6120 firmware. The function fails to properly validate the length of user-supplied input through the host argument before copying it into a fixed-size buffer. When an attacker provides an overly long input string, it overflows the designated buffer space, potentially overwriting adjacent memory regions including return addresses and other critical data structures.

The vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer) and CWE-120 (Buffer Copy without Checking Size of Input), indicating a classic buffer overflow scenario where boundary checking is insufficient or absent. This type of vulnerability in embedded network devices is particularly concerning as it can lead to complete device compromise.

Root Cause

The root cause of this vulnerability is the absence of proper bounds checking in the sub_30394 function when processing the host parameter. The firmware code copies user-controlled data into a stack or heap buffer without verifying that the input length does not exceed the allocated buffer size. This oversight allows attackers to supply malicious input that exceeds the buffer boundary, corrupting adjacent memory and potentially hijacking program execution flow.

Attack Vector

The vulnerability can be exploited remotely over the network by an authenticated attacker. The attack requires low privileges and no user interaction, making it relatively straightforward to exploit once an attacker has gained access to the device's management interface. The attacker manipulates the host argument with crafted input designed to overflow the vulnerable buffer, potentially achieving code execution in the context of the affected firmware process.

The attack surface is related to the Wi-Fi 2.4GHz on/off scheduling functionality (wifi_2g_onoff_sche), as indicated by the proof-of-concept documentation. For detailed technical analysis of the exploitation mechanism, see the GitHub PoC Repository.

Detection Methods for CVE-2025-4140

Indicators of Compromise

• Unexpected device reboots or instability in Netgear EX6120 range extenders
• Anomalous network traffic originating from or directed to the device management interface
• Unusual HTTP requests targeting the Wi-Fi scheduling configuration endpoints with abnormally long parameter values
• Evidence of memory corruption or crash dumps in device logs if available

Detection Strategies

• Deploy network intrusion detection systems (IDS) with rules to identify buffer overflow attack patterns targeting embedded devices
• Monitor for unusually large HTTP request parameters in traffic destined for Netgear device management interfaces
• Implement deep packet inspection to detect malformed requests containing potential shellcode or NOP sleds
• Use SentinelOne Singularity to monitor network endpoints for lateral movement attempts originating from compromised IoT devices

Monitoring Recommendations

• Enable logging on network firewalls to capture all management traffic to Netgear EX6120 devices
• Implement network segmentation to isolate IoT devices and limit the blast radius of potential compromises
• Regularly audit device firmware versions across the network to identify vulnerable Netgear EX6120 units
• Configure alerts for multiple failed authentication attempts or unusual access patterns to device management interfaces

How to Mitigate CVE-2025-4140

Immediate Actions Required

• Restrict network access to the Netgear EX6120 management interface to trusted IP addresses only
• Place the device behind a firewall and disable remote management if not required
• Monitor for firmware updates from Netgear and apply patches as soon as they become available
• Consider replacing the affected device with a supported model if no patch is forthcoming

Patch Information

At the time of disclosure, Netgear was contacted about this vulnerability but did not respond. No official security patch is currently available from the vendor. Users should monitor the Netgear Official Website for security advisories and firmware updates. Given the vendor's lack of response, organizations should evaluate their risk exposure and consider alternative mitigation measures or device replacement.

Workarounds

• Implement network access control lists (ACLs) to restrict access to the device management interface from untrusted networks
• Disable Wi-Fi scheduling features if not operationally required, as the vulnerability is associated with this functionality
• Deploy network-level firewalls to filter malicious traffic before it reaches the vulnerable device
• Consider network isolation for the affected device to contain potential compromise impact

# Example firewall rule to restrict management interface access (iptables)
# Replace 192.168.1.100 with the IP of your Netgear EX6120
# Replace 192.168.1.0/24 with your trusted management subnet

iptables -A FORWARD -d 192.168.1.100 -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A FORWARD -d 192.168.1.100 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.1.100 -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A FORWARD -d 192.168.1.100 -p tcp --dport 443 -j DROP