Stack-based Buffer Overflow in Edimax EW-7478APC

A stack-based buffer overflow vulnerability has been identified in the Edimax EW-7478APC router, specifically within firmware version 1.04. The vulnerability resides in the formWanTcpipSetup function, accessible via the /goform/formWanTcpipSetup endpoint. An authenticated remote attacker can trigger this overflow by sending a specially crafted input to the pppUserName parameter. This flaw allows for the execution of arbitrary code on the affected device or can result in a denial-of-service condition. Publicly available exploit code exists, increasing the risk of exploitation. The vendor has not provided a patch or response to the disclosure. Defenders should note that this vulnerability requires authenticated access, but its remote nature and the availability of exploit material pose a significant risk to internal network segments where these devices are deployed.

Attack Chain

1. Attacker performs network reconnaissance to identify reachable Edimax EW-7478APC management interfaces.
2. Attacker obtains valid administrative or user credentials via secondary means (e.g., credential stuffing or default password exploitation).
3. Attacker authenticates to the web-based management interface.
4. Attacker crafts a malicious HTTP POST request targeting the /goform/formWanTcpipSetup endpoint.
5. Attacker injects a long string payload into the pppUserName parameter of the POST body.
6. The web server process fails to perform sufficient boundary checks on the pppUserName input before copying it into a stack-based buffer.
7. The overflow overwrites the return address, enabling redirection of execution flow to arbitrary attacker-supplied shellcode.
8. Final objective is achieved: arbitrary command execution or system crash.

Impact

Successful exploitation allows for complete compromise of the router, potentially providing an attacker with a pivot point into the local network. With a CVSS v3.1 score of 9.9, this vulnerability represents a critical risk to small office and home office (SOHO) deployments. If exploited, attackers could intercept traffic, perform man-in-the-middle attacks, or deploy further malicious payloads. Given the lack of a vendor patch, the only effective mitigation is to restrict management interface access to trusted networks or replace affected hardware.

Recommendation

• Restrict access to the management web interface of all Edimax EW-7478APC devices to a dedicated management VLAN or trusted IP addresses via firewall rules.
• Monitor internal network traffic for unauthorized HTTP POST requests directed at /goform/formWanTcpipSetup.
• Audit logs for failed authentication attempts preceding any interaction with management endpoints.
• Isolate affected devices from the internet until a firmware update is provided by the vendor.