Tenda F456 Stack-Based Buffer Overflow Vulnerability

A critical stack-based buffer overflow vulnerability, identified as CVE-2026-6196, affects Tenda F456 routers running firmware version 1.0.0.5. The vulnerability resides within the 'fromexeCommand' function of the '/goform/exeCommand' file. A remote attacker can exploit this vulnerability by sending a specially crafted request that manipulates the 'cmdinput' argument, leading to arbitrary code execution on the device. Publicly available exploits exist, increasing the risk of widespread exploitation and potential compromise of vulnerable Tenda F456 routers. This poses a significant threat to home and small business networks relying on these devices.

Attack Chain

1. The attacker identifies a Tenda F456 router running firmware version 1.0.0.5 exposed to the internet.
2. The attacker crafts a malicious HTTP request targeting the /goform/exeCommand endpoint.
3. The crafted request includes the cmdinput argument with a payload exceeding the buffer size allocated for it.
4. The router's web server processes the request and passes the oversized cmdinput to the fromexeCommand function.
5. The fromexeCommand function attempts to write the oversized input to a fixed-size buffer on the stack.
6. This write operation overflows the buffer, overwriting adjacent memory locations on the stack, including the return address.
7. The attacker controls the overwritten return address to point to malicious code injected as part of the overflowed payload.
8. When the fromexeCommand function returns, execution jumps to the attacker-controlled code, resulting in arbitrary code execution on the router.

Impact

Successful exploitation of this vulnerability allows a remote attacker to execute arbitrary code on the affected Tenda F456 router. This can lead to complete compromise of the device, allowing the attacker to control its functionality, potentially including intercepting network traffic, modifying router settings, and using the router as a pivot point to attack other devices on the network. Given the prevalence of Tenda routers in home and small business environments, a large number of devices are potentially vulnerable.

Recommendation

• Apply any available patches or firmware updates released by Tenda for the F456 router to address CVE-2026-6196.
• If a patch is unavailable, consider replacing the vulnerable device with a more secure alternative.
• Monitor network traffic for suspicious requests targeting the /goform/exeCommand endpoint on Tenda F456 routers. Deploy the Sigma rule "Detect Tenda F456 Buffer Overflow Attempt" to identify potential exploitation attempts.
• Implement network segmentation to limit the impact of a compromised router on other devices on the network.
• Enable logging on the Tenda router to aid in incident investigation and analysis.