CVE-2026-9426 - Edimax EW-7438RPn Stack-Based Buffer Overflow

A stack-based buffer overflow vulnerability, identified as CVE-2026-9426, affects Edimax EW-7438RPn version 1.31. This flaw resides within the formHwSet function of the /goform/formHwSet file. The vulnerability is triggered through the manipulation of several arguments including Anntena, Mcs, regDomain, nic0Addr, nic1Addr, wlanAddr, wanAddr, wlanSSID, wlanChan, initgain, txcck, txofdm, and submit-url. A remote attacker can exploit this vulnerability to potentially execute arbitrary code on the affected device. Public exploits are available, increasing the risk of exploitation. The vendor was notified but has not responded.

Attack Chain

1. The attacker identifies an Edimax EW-7438RPn device running firmware version 1.31 accessible over the network.
2. The attacker crafts a malicious HTTP request targeting the /goform/formHwSet endpoint.
3. Within the HTTP request, the attacker includes a long string in one or more of the vulnerable parameters: Anntena, Mcs, regDomain, nic0Addr, nic1Addr, wlanAddr, wanAddr, wlanSSID, wlanChan, initgain, txcck, txofdm, or submit-url.
4. The device processes the HTTP request, passing the attacker-controlled input to the formHwSet function without proper bounds checking.
5. The oversized input overflows the stack buffer allocated for the affected parameter(s).
6. The stack overflow overwrites critical data, including the return address, on the stack.
7. The attacker redirects control to an attacker-controlled address.
8. The attacker executes arbitrary code on the device, potentially gaining full control.

Impact

Successful exploitation of this vulnerability allows a remote attacker to execute arbitrary code on the Edimax EW-7438RPn device. This could lead to complete compromise of the device, allowing the attacker to eavesdrop on network traffic, modify device settings, or use the device as a launchpad for further attacks on the internal network. Given the nature of the vulnerability and the lack of vendor response, many devices may be vulnerable.

Recommendation

• Deploy the Sigma rule Detect CVE-2026-9426 Exploitation Attempt via Long URI to detect potential exploitation attempts by identifying abnormally long request parameters (cs-uri-query) targeting the vulnerable endpoint.
• Implement rate limiting on requests to the /goform/formHwSet endpoint to mitigate brute-force exploitation attempts (log source: webserver).
• Monitor web server logs for POST requests with unusually long parameters related to Anntena, Mcs, regDomain, nic0Addr, nic1Addr, wlanAddr, wanAddr, wlanSSID, wlanChan, initgain, txcck, txofdm, or submit-url in the URI (log source: webserver).