CVE-2025-4139 Overview
CVE-2025-4139 is a buffer overflow vulnerability affecting Netgear EX6120 WiFi range extenders running firmware version 1.0.0.68. The flaw resides in the fwAcosCgiInbound function, where improper handling of the host argument allows attackers to corrupt memory through unbounded input. Remote exploitation is possible over the network, and only low-privilege authentication is required to reach the vulnerable code path. The vendor was contacted prior to public disclosure but did not respond, leaving affected devices without an official fix. The vulnerability is classified under CWE-119 for improper restriction of operations within the bounds of a memory buffer.
Critical Impact
Remote attackers with low privileges can trigger memory corruption in the device's web management interface, potentially leading to arbitrary code execution or denial of service on affected Netgear EX6120 extenders.
Affected Products
- Netgear EX6120 hardware device
- Netgear EX6120 firmware version 1.0.0.68
- Web management component invoking fwAcosCgiInbound
Discovery Timeline
- 2025-04-30 - CVE-2025-4139 published to NVD
- 2025-06-23 - Last updated in NVD database
Technical Details for CVE-2025-4139
Vulnerability Analysis
The vulnerability exists in the fwAcosCgiInbound function, a CGI handler within the EX6120 web management interface. The function processes the host parameter from inbound HTTP requests without enforcing length validation before copying the value into a fixed-size buffer. An attacker who supplies an oversized host value can overflow the destination buffer and corrupt adjacent memory regions on the stack or heap.
The attack vector is network-based and requires low-privilege authentication. Once exploited, the overflow can disrupt normal operation of the extender or, depending on memory layout and protections, enable arbitrary code execution in the context of the web service. Because the EX6120 is a consumer-grade network device, successful exploitation can lead to full compromise of the extender and pivoting opportunities within the local network.
Root Cause
The root cause is missing bounds checking on attacker-controlled input passed through the host argument. The vulnerable CGI handler copies user-supplied data into a fixed-length buffer using unsafe string operations, violating the safe memory-handling expectations documented in CWE-119. Embedded firmware of this class frequently lacks modern exploit mitigations such as stack canaries or address space layout randomization, increasing exploitability.
Attack Vector
Exploitation requires network reachability to the EX6120 management interface. An attacker crafts an HTTP request directed at the CGI endpoint backed by fwAcosCgiInbound and supplies an oversized host parameter. See the GitHub PoC Repository and VulDB entry #306631 for technical details on the request structure used to trigger the overflow.
Detection Methods for CVE-2025-4139
Indicators of Compromise
- Unusual or oversized host header values in HTTP requests directed at the EX6120 administrative interface.
- Unexpected reboots, crashes, or service restarts of the extender's web management daemon.
- Outbound connections from the extender to unknown external hosts following inbound HTTP traffic.
- Configuration changes to the extender not initiated by an administrator.
Detection Strategies
- Inspect HTTP request logs at network choke points for abnormally long host parameters targeting EX6120 management URLs.
- Monitor for repeated connection attempts to the extender's web interface from internal or external sources.
- Use network intrusion detection signatures that flag oversized CGI parameter values aimed at consumer router firmware.
Monitoring Recommendations
- Aggregate network telemetry from segments containing IoT and consumer networking devices for centralized review.
- Track device availability and management-interface response patterns to detect crash-and-reboot cycles.
- Alert on new or unauthorized administrative sessions to the EX6120 web interface.
How to Mitigate CVE-2025-4139
Immediate Actions Required
- Restrict access to the EX6120 web management interface to trusted management networks using firewall or VLAN segmentation.
- Disable remote management on the extender so the administrative interface is unreachable from the WAN.
- Change default credentials and enforce strong authentication on the management interface to reduce the pool of low-privilege attackers.
- Inventory affected devices running firmware 1.0.0.68 and prioritize them for replacement or isolation.
Patch Information
No vendor patch has been published for CVE-2025-4139 at the time of NVD publication. The Netgear official website should be monitored for firmware updates addressing the fwAcosCgiInbound flaw. Organizations should consult VulDB CTI #306631 for ongoing tracking of vendor response status.
Workarounds
- Place the EX6120 behind a network segment that blocks untrusted HTTP traffic to the device's management port.
- Replace the affected extender with a supported model if a firmware update is not made available by the vendor.
- Apply web application firewall rules that drop HTTP requests containing oversized host parameters destined for the device.
- Disable the device's CGI-based management features where alternative provisioning methods are available.
# Example: block external access to the EX6120 management interface with iptables
# Replace 192.0.2.10 with the EX6120 IP and 80/443 with the management ports in use
iptables -A FORWARD -d 192.0.2.10 -p tcp --dport 80 -m iprange ! --src-range 10.0.0.0-10.0.0.255 -j DROP
iptables -A FORWARD -d 192.0.2.10 -p tcp --dport 443 -m iprange ! --src-range 10.0.0.0-10.0.0.255 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
