CVE-2025-4140: Netgear Ex6120 Buffer Overflow Vulnerability

CVE-2025-4140 Overview

CVE-2025-4140 is a buffer overflow vulnerability in the Netgear EX6120 WiFi range extender running firmware version 1.0.3.94. The flaw resides in the sub_30394 function, where manipulation of the host argument triggers memory corruption. Attackers can exploit this issue remotely over the network without user interaction.

The vulnerability is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer) and [CWE-120] (Classic Buffer Overflow). Netgear was contacted regarding this disclosure but did not respond, leaving affected devices without an official vendor patch at the time of publication.

Critical Impact
Remote attackers with low privileges can corrupt memory on affected Netgear EX6120 devices, potentially leading to arbitrary code execution or denial of service on the extender.

Affected Products

Netgear EX6120 (hardware)
Netgear EX6120 firmware version 1.0.3.94
Deployments using the WiFi 2.4GHz on/off scheduling functionality

Discovery Timeline

2025-04-30 - CVE-2025-4140 published to NVD
2025-05-12 - Last updated in NVD database

Technical Details for CVE-2025-4140

Vulnerability Analysis

The vulnerability resides in the sub_30394 function within the Netgear EX6120 firmware. This function handles request parameters tied to the WiFi 2.4GHz on/off scheduling feature. When the host argument is processed, the function fails to validate the input length before copying data into a fixed-size buffer.

This classic buffer overflow condition allows an attacker to write data beyond the allocated buffer boundaries. The overflow can overwrite adjacent stack or heap memory, including return addresses and function pointers. Successful exploitation can lead to control flow hijacking on the embedded MIPS or ARM processor used by the extender.

Because the EX6120 operates as a network-attached device, exploitation does not require physical access. An attacker on the same network segment, or one able to reach the device's management interface, can deliver the malicious host value through crafted HTTP requests.

Root Cause

The root cause is insufficient bounds checking on user-supplied input in the sub_30394 function. The function copies the attacker-controlled host parameter into a destination buffer without verifying its length, violating safe memory handling practices common in resource-constrained embedded firmware.

Attack Vector

The attack vector is network-based and requires low privileges. An attacker sends a crafted HTTP request containing an oversized host parameter to the vulnerable endpoint exposed by the EX6120 web management interface. No user interaction is required to trigger the overflow.

A public proof-of-concept describing the overflow location and trigger conditions has been published in the GitHub PoC Repository, increasing the likelihood of exploitation attempts against exposed devices.

Detection Methods for CVE-2025-4140

Indicators of Compromise

Unusual HTTP POST requests targeting the WiFi 2.4GHz scheduling endpoint on EX6120 devices
Requests containing abnormally long host parameter values exceeding typical hostname lengths
Unexpected reboots, crashes, or service interruptions on the EX6120 management interface
Outbound connections from the extender to unknown external IP addresses

Detection Strategies

Inspect HTTP traffic to EX6120 management interfaces for parameter values that exceed RFC 1035 hostname length limits (253 characters)
Deploy network intrusion detection signatures matching oversized host argument patterns directed at Netgear extender endpoints
Monitor administrative interfaces of consumer-grade network devices for anomalous request patterns and authentication failures

Monitoring Recommendations

Log all administrative access to EX6120 devices and forward logs to a centralized SIEM for correlation
Track device uptime and configuration changes to detect crash-and-restart patterns indicative of exploitation attempts
Enable alerts when network devices initiate unexpected outbound traffic, which may indicate post-exploitation activity

How to Mitigate CVE-2025-4140

Immediate Actions Required

Restrict access to the EX6120 web management interface to trusted internal networks only and block external access
Disable remote management features if not actively required for operations
Place EX6120 devices behind a firewall and segment them from sensitive corporate assets
Audit Netgear EX6120 inventory and identify any devices running firmware 1.0.3.94

Patch Information

At the time of publication, Netgear had not responded to the disclosure and no official patch is available. Monitor the Netgear Official Website for security advisories and firmware updates addressing this issue. Organizations should evaluate whether to retire affected EX6120 units in favor of supported hardware if no fix is released.

Workarounds

Change default administrative credentials on all EX6120 devices to strong, unique passwords
Disable the WiFi 2.4GHz scheduling feature if it is not in active use
Isolate WiFi extenders on a dedicated VLAN with strict access control lists
Consider replacing unsupported consumer extenders with enterprise-grade access points that receive timely security updates

bash

# Example firewall rule to restrict EX6120 management access
# Allow only the admin workstation to reach the extender web UI
iptables -A FORWARD -s 192.168.10.50 -d 192.168.1.100 -p tcp --dport 80 -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 -j DROP