Edimax EW-7438RPn formLogout stack-based overflow

Vulnerability

A stack-based buffer overflow exists in the formLogout function of the Edimax EW-7438RPn wireless extender running firmware version 1.31. The vulnerability resides in the /goform/formLogout endpoint, where the submit-url parameter is copied into a fixed-size stack buffer without any length validation. This allows an attacker to overflow the buffer by supplying an excessively long string. The issue is reachable remotely via an HTTP POST request, and no authentication is required to trigger the overflow [1].

Exploitation

An attacker can exploit this vulnerability by sending a crafted HTTP POST request to the /goform/formLogout endpoint with an overly long submit-url parameter. The provided proof-of-concept uses a string of repeated 'a' characters to cause a crash. The exploit does not require prior authentication, and the attack can be launched from any network-accessible position. The exploit code has been publicly disclosed [1].

Impact

Successful exploitation leads to a stack buffer overflow, overwriting the return address of the formLogout function. This can result in a denial of service (device crash) or, with careful control of the overflow data, arbitrary code execution with the privileges of the web server process (typically root on embedded devices). The attacker gains full control of the affected device [1].

Mitigation

As of the publication date, no official patch or firmware update has been released by Edimax. The vendor was contacted but did not respond to the disclosure. Users should restrict network access to the device, disable remote management features, and isolate the extender from untrusted networks. If possible, consider replacing the device with a supported alternative that receives security updates.