Tenda CH22 Stack-Based Buffer Overflow Vulnerability (CVE-2026-5204)

CVE-2026-5204 describes a critical stack-based buffer overflow vulnerability affecting Tenda CH22 router version 1.0.0.1. The vulnerability resides within the formWebTypeLibrary function in the /goform/webtypelibrary file, which handles web-based parameter input. An attacker can exploit this vulnerability by sending a specially crafted HTTP request to the router, manipulating the webSiteId argument to overwrite the stack buffer. This allows for arbitrary code execution on the device. Given the router’s role as a network gateway, successful exploitation can lead to complete compromise of the device and potentially the entire network behind it. The availability of a public exploit increases the risk of widespread exploitation.

Attack Chain

1. The attacker identifies a vulnerable Tenda CH22 router running firmware version 1.0.0.1.
2. The attacker crafts a malicious HTTP POST request targeting the /goform/webtypelibrary endpoint.
3. The crafted request includes the webSiteId parameter with a payload exceeding the expected buffer size, triggering the stack-based buffer overflow in the formWebTypeLibrary function.
4. The overflow overwrites critical data on the stack, including the return address.
5. The overwritten return address is replaced with the address of malicious code injected into the payload or a pre-existing code location within the router’s firmware (Return-Oriented Programming - ROP).
6. The formWebTypeLibrary function returns, transferring control to the attacker-controlled code.
7. The attacker’s code executes, granting the attacker control over the device.
8. The attacker can then use this control to further compromise the network or disrupt services.

Impact

Successful exploitation of CVE-2026-5204 allows a remote attacker to execute arbitrary code on the vulnerable Tenda CH22 router. This can lead to complete control of the device, enabling the attacker to intercept network traffic, modify DNS settings, create VPNs, or launch further attacks on devices within the network. Given that routers are essential network devices, a successful attack can have a significant impact, affecting all connected devices and potentially exposing sensitive data.

Recommendation

• Apply available firmware updates for Tenda CH22 routers immediately to patch CVE-2026-5204.
• Deploy the Sigma rule Tenda-CH22-WebSiteId-Buffer-Overflow to detect exploitation attempts targeting the vulnerable endpoint.
• Monitor web server logs for suspicious POST requests to /goform/webtypelibrary with unusually long webSiteId parameters, as indicated by WebSiteId_Length_Detection Sigma rule.
• Implement network segmentation to limit the impact of a potential router compromise.