Edimax EW-7438RPn Stack-Based Buffer Overflow Vulnerability (CVE-2026-9459)

A stack-based buffer overflow vulnerability, identified as CVE-2026-9459, affects the Edimax EW-7438RPn version 1.31. The vulnerability resides within the formConnectionSetting function located in the /goform/formConnectionSetting file. Successful exploitation allows a remote attacker to potentially execute arbitrary code on the device. The root cause is improper input validation on the max_Conn and timeOut arguments, leading to a buffer overflow when these arguments are manipulated. Publicly available exploit code exists, increasing the risk of widespread exploitation. The vendor has been unresponsive to disclosure attempts.

Attack Chain

1. The attacker identifies a vulnerable Edimax EW-7438RPn 1.31 device exposed to the internet.
2. The attacker crafts a malicious HTTP request targeting the /goform/formConnectionSetting endpoint.
3. Within the HTTP request, the attacker manipulates the max_Conn or timeOut arguments with an overly long string.
4. The vulnerable formConnectionSetting function processes the request without proper bounds checking.
5. The oversized input overflows the stack buffer, overwriting adjacent memory regions.
6. The attacker carefully crafts the overflow to overwrite the return address with the address of malicious code.
7. The function returns, diverting execution to the attacker-controlled code.
8. The attacker achieves arbitrary code execution on the device, potentially gaining full control.

Impact

Successful exploitation of CVE-2026-9459 can lead to complete compromise of the Edimax EW-7438RPn device. This could allow attackers to reconfigure the device, intercept network traffic, or use the device as a foothold for further attacks on the local network. Given the widespread use of such devices, a significant number of home and small business networks could be affected. The lack of vendor response makes patching unlikely, extending the window of vulnerability.

Recommendation

• Apply web application firewall rules to filter requests to /goform/formConnectionSetting containing excessively long max_Conn or timeOut parameters, mitigating exploitation attempts.
• Monitor web server logs (category webserver) for POST requests to /goform/formConnectionSetting with unusually long cs-uri-query parameters, corresponding to potential buffer overflow attempts.
• Deploy the Sigma rule “Detect CVE-2026-9459 Exploitation Attempt” to detect suspicious requests exploiting this vulnerability.
• Consider replacing affected Edimax EW-7438RPn devices with patched or more secure alternatives, given the lack of vendor support.