Attack Chain

1. Attacker performs network reconnaissance to identify Tenda W20E devices exposed to the internet.
2. Attacker establishes an authenticated session with the target device.
3. Attacker crafts an HTTP POST request targeting the /goform/editQos endpoint.
4. Attacker inserts a specially crafted, oversized value into the qosListConnecttedNum parameter.
5. The application passes the input to the vulnerable lstAdd function without proper bounds checking.
6. The excessive data overflows the allocated buffer on the stack.
7. The attacker overwrites return addresses or other critical stack data to hijack the control flow.
8. Execution of arbitrary code or denial of service is achieved on the affected device.

Impact

Successful exploitation of this vulnerability allows for remote code execution on the Tenda W20E router. Given the position of these devices as network gateways, an attacker gaining code execution could facilitate lateral movement into the protected network, intercept traffic, or perform man-in-the-middle attacks. As of the time of reporting, the vulnerability is public and exploit material is accessible, increasing the likelihood of opportunistic exploitation against vulnerable firmware versions.

Recommendation

Prioritized actions for security operations and IT teams:

• Check internal inventory for Tenda W20E devices running the affected firmware version 15.11.0.6(1068_1546_841)_CN_TDC.
• Apply the latest security patches provided by Tenda if available for this model.
• Restrict access to the device web administration interface (/goform/editQos) to trusted management subnets only.
• Deploy web application firewall (WAF) or intrusion detection system (IDS) rules to inspect and block HTTP requests containing abnormally long strings in the qosListConnecttedNum argument.