Edimax EW-7438RPn webs formWirelessTbl buffer overflow

Vulnerability

A stack buffer overflow vulnerability exists in the Edimax EW-7438RPn wireless extender firmware version 1.31 and earlier. The flaw resides in the formWirelessTbl function within the webs binary, accessible via the /goform/formWirelessTbl endpoint. The submit-url parameter is copied directly into a stack-based buffer without any length validation, allowing an attacker to overflow the buffer and overwrite the return address [1].

Exploitation

An attacker with network access to the device's web interface and valid administrative credentials can exploit this vulnerability. By sending a crafted POST request to /goform/formWirelessTbl with an excessively long submit-url value (e.g., a string of 'a' characters), the stack is overflowed, causing a crash or potentially redirecting execution flow [1]. The provided proof-of-concept demonstrates a request with a 1648-byte payload that triggers the overflow.

Impact

Successful exploitation can result in denial of service (device crash) or arbitrary code execution at the privilege level of the webs process, which typically runs with root privileges on such embedded devices. This would allow an attacker to fully compromise the extender, potentially gaining persistent access and using it as a pivot point within the network [1].

Mitigation

As of the publication date, the vendor has not responded to the disclosure and no official patch has been released. Users of the Edimax EW-7438RPn with firmware version 1.31 or earlier are advised to restrict network access to the web administration interface, change default credentials, and consider replacing the device if a fix becomes unavailable. No workaround is provided by the vendor [1].