Attack Chain

1. The attacker identifies a Tenda F1202 router running firmware version 1.2.0.20(408).
2. The attacker crafts a malicious HTTP request targeting the /goform/WrlExtraSet endpoint.
3. Within the HTTP request, the attacker includes the delno argument with a value exceeding the buffer’s capacity in the formWrlExtraSet function.
4. The vulnerable formWrlExtraSet function processes the delno argument without proper bounds checking.
5. The excessive data provided in the delno argument overwrites the stack.
6. The attacker injects malicious code into the overflowed buffer.
7. The injected code is executed, granting the attacker control over the device.
8. The attacker can then perform actions such as modifying router settings, intercepting network traffic, or establishing a backdoor for persistent access.

Impact

Successful exploitation of CVE-2026-9429 allows an attacker to gain complete control over the Tenda F1202 router. This can lead to a variety of malicious activities, including data theft, denial of service, and the establishment of a persistent foothold on the network. Given the availability of a public exploit, organizations and individuals using the affected Tenda F1202 router are at significant risk.

Recommendation

• Apply available patches or firmware updates from Tenda to address CVE-2026-9429.
• Monitor web server logs for suspicious POST requests to /goform/WrlExtraSet with abnormally long delno arguments, using the Sigma rule Detect Suspiciously Long delno Parameter in Tenda Routers.
• Implement network intrusion detection systems (IDS) rules to detect and block exploitation attempts targeting CVE-2026-9429.
• Review and restrict access to the router’s management interface to trusted IP addresses only.
• Enable logging on the Tenda router and forward logs to a SIEM for centralized monitoring and analysis.