Multiple Linksys range extenders are vulnerable to a critical stack-based buffer overflow that could allow remote attackers to achieve arbitrary code execution.

This is a stack-based buffer overflow (CWE-121) occurring in the portRangeForwardAdd function within the /goform/portRangeForwardAdd endpoint. An attacker with low-level privileges can supply oversized inputs to parameters including ruleName, schedule, inboundFilter, TCPPorts, or UDPPorts to overwrite the return address on the stack.

Successful exploitation of this vulnerability allows an attacker to execute arbitrary code with system-level privileges or cause a persistent denial-of-service by crashing the router. Given the CVSS score of 8.8, this poses a severe risk to network integrity and confidentiality. Compromise of network infrastructure devices can facilitate lateral movement, traffic interception, and total loss of administrative control over the local network segment.

Immediate Action: As there is currently no official patch from the vendor, users should restrict administrative access to these devices to trusted management IP addresses only and disable remote management features.

Proactive Monitoring: Monitor network logs for unusual POST requests directed at the /goform/portRangeForwardAdd endpoint and watch for frequent device reboots or service outages that may indicate crash attempts.

Compensating Controls: Deploy a Web Application Firewall (WAF) or an Intrusion Prevention System (IPS) capable of inspecting HTTP POST traffic to drop requests containing abnormally long strings in the specified parameters.

Public Exploit Available: Yes, a proof-of-concept is publicly available via a researcher write-up on GitHub.

Given the absence of a vendor-provided patch and the availability of a functional proof-of-concept, this vulnerability represents a significant risk. Administrators should immediately isolate these devices from external access and implement strict firewall rules to limit interaction with the administrative web interface until official firmware updates are released.