CVE-2026-5204: Tenda CH22 Buffer Overflow Vulnerability

CVE-2026-5204 Overview

CVE-2026-5204 is a stack-based buffer overflow vulnerability in the Tenda CH22 router running firmware version 1.0.0.1. The flaw resides in the formWebTypeLibrary function within /goform/webtypelibrary, part of the Parameter Handler component. Attackers can trigger the overflow by manipulating the webSiteId parameter over the network. The exploit details have been publicly disclosed, increasing the likelihood of attempted exploitation against exposed devices.

Critical Impact
Remote attackers with low privileges can corrupt stack memory on Tenda CH22 routers, leading to arbitrary code execution or denial of service against the device.

Affected Products

Tenda CH22 hardware (all units running the affected firmware)
Tenda CH22 Firmware version 1.0.0.1
Parameter Handler component exposing /goform/webtypelibrary

Discovery Timeline

2026-03-31 - CVE-2026-5204 published to NVD
2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-5204

Vulnerability Analysis

The vulnerability is a stack-based buffer overflow [CWE-121] tracked under the broader categories of improper memory buffer restriction [CWE-119] and out-of-bounds write [CWE-787]. The formWebTypeLibrary handler processes the webSiteId query argument supplied to /goform/webtypelibrary without enforcing a length check before copying the value into a fixed-size stack buffer. An attacker who can reach the router's web management interface can submit an oversized webSiteId value to overwrite the saved return address on the stack.

Successful exploitation impacts confidentiality, integrity, and availability of the device. On MIPS- and ARM-based SOHO routers like the CH22, a controlled overflow typically results in process crash or remote code execution as the web daemon, which generally runs with elevated privileges. The attack requires network reachability to the device management interface and a low-privilege session, but no user interaction.

Root Cause

The root cause is missing input validation on the webSiteId parameter. The handler copies attacker-supplied data into a stack buffer using an unbounded string operation, allowing data beyond the buffer boundary to overwrite adjacent stack frames, including saved registers and the return address.

Attack Vector

Exploitation occurs over the network against the HTTP management interface. An attacker sends a crafted POST or GET request to /goform/webtypelibrary containing an oversized webSiteId argument. A public proof-of-concept is referenced in the GitHub PoC Repository and VulDB #354332. Devices with the management interface exposed to the WAN face the highest risk.

No verified exploitation code available - see the linked PoC repository for technical details.

Detection Methods for CVE-2026-5204

Indicators of Compromise

HTTP requests to /goform/webtypelibrary containing abnormally long webSiteId parameter values
Repeated crashes or reboots of the Tenda CH22 web management daemon
Unexpected outbound connections from the router following management-interface traffic
Configuration changes or new firewall rules added without administrator action

Detection Strategies

Inspect HTTP traffic destined for the router for webSiteId argument lengths exceeding typical bounds (a few dozen bytes)
Alert on POST requests to /goform/webtypelibrary originating from untrusted network segments
Correlate router process crashes with preceding HTTP requests to the affected endpoint

Monitoring Recommendations

Forward router syslog and management-plane logs to a centralized SIEM for anomaly review
Monitor for unexpected DNS, DHCP, or routing changes on devices running CH22 firmware 1.0.0.1
Track outbound traffic from router management VLANs to identify post-exploitation command-and-control activity

How to Mitigate CVE-2026-5204

Immediate Actions Required

Restrict access to the router's web management interface to trusted internal hosts only
Disable WAN-side remote management on all Tenda CH22 devices
Place affected devices behind a network segmentation boundary that blocks untrusted HTTP traffic to /goform/*
Audit administrative credentials and rotate any shared or default passwords

Patch Information

No vendor advisory or patch has been published at the time of writing. Refer to the Tenda Official Website for firmware updates and check VulDB #354332 for advisory tracking. Replace end-of-life CH22 hardware if the vendor does not issue a fixed firmware release.

Workarounds

Block external access to TCP ports used by the router web interface (typically 80/443) at the upstream firewall
Apply ACLs that permit /goform/webtypelibrary requests only from designated administrator IP addresses
Disable the affected web management feature where feasible until a patched firmware is available

bash

# Example iptables rule to restrict management interface access to a trusted admin subnet
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP