CVE-2026-36777 Overview
CVE-2026-36777 is a stack overflow vulnerability in the Tenda W3 Wireless Router firmware version v1.0.0.3(2204). The flaw resides in the formSetCfm function, where the param_1 parameter is processed without proper bounds checking. An attacker on an adjacent network can send a crafted HTTP request to trigger the overflow and cause a Denial of Service (DoS) condition. The vulnerability is classified under CWE-121: Stack-based Buffer Overflow.
Critical Impact
Adjacent network attackers can crash the router and disrupt wireless connectivity for all connected clients without authentication.
Affected Products
- Shenzhen Tenda Technology Co., Ltd Tenda W3 Wireless Router
- Firmware version v1.0.0.3(2204)
- Devices exposing the web management interface on the local network
Discovery Timeline
- 2026-06-09 - CVE-2026-36777 published to NVD
- 2026-06-10 - Last updated in NVD database
Technical Details for CVE-2026-36777
Vulnerability Analysis
The vulnerability exists in the formSetCfm handler within the Tenda W3 router's web management application. The function processes the param_1 HTTP request parameter and copies attacker-controlled data into a fixed-size stack buffer without validating the input length. When an oversized value is supplied, the copy operation writes past the buffer boundary and corrupts adjacent stack memory, including the saved return address.
Exploitation requires network adjacency, meaning the attacker must be on the same wireless or local network segment as the target router. No authentication or user interaction is required. The current impact is limited to availability — the device crashes and reboots — but stack-based buffer overflows of this class can sometimes be escalated to code execution depending on memory layout and mitigations present in the firmware.
Root Cause
The root cause is missing length validation on the param_1 HTTP parameter before it is written into a stack-allocated buffer inside formSetCfm. The function relies on unsafe string copy semantics rather than bounded copy primitives, allowing a long input to overflow the destination buffer.
Attack Vector
An attacker connected to the same network as the Tenda W3 sends a crafted HTTP POST request to the router's web administration endpoint that invokes formSetCfm. The request includes an oversized param_1 value designed to exceed the stack buffer capacity. Processing the request corrupts the stack and forces the HTTP service or the device to crash, resulting in denial of service. A public proof of concept is available in the GitHub PoC Repository.
The vulnerability manifests when the formSetCfm handler reads param_1 from the incoming HTTP request and copies it into a local stack buffer. See the referenced PoC repository for request structure and payload details.
Detection Methods for CVE-2026-36777
Indicators of Compromise
- Unexpected reboots or service restarts of the Tenda W3 router
- HTTP POST requests to administrative endpoints invoking formSetCfm with abnormally long parameter values
- Loss of wireless connectivity for clients followed by router DHCP renegotiation events
Detection Strategies
- Inspect inbound HTTP traffic to the router management interface for requests containing oversized param_1 values targeting formSetCfm
- Monitor router uptime and crash logs for repeated unexplained restarts correlated with management-interface traffic
- Deploy network intrusion detection signatures that flag HTTP requests exceeding reasonable length thresholds for known Tenda form handlers
Monitoring Recommendations
- Log all HTTP requests reaching the router administration interface and alert on requests originating from non-administrative hosts
- Track wireless client disconnect storms as a potential signal of router DoS activity
- Restrict management-interface access to a dedicated VLAN and monitor that segment for anomalous traffic patterns
How to Mitigate CVE-2026-36777
Immediate Actions Required
- Disable remote management on the WAN interface and restrict administration access to trusted hosts only
- Segment the router management interface onto an isolated VLAN inaccessible to general wireless clients
- Audit the network for unauthorized devices that could be used to reach the adjacent network
Patch Information
No vendor patch is referenced in the NVD entry for CVE-2026-36777 at the time of publication. Monitor the Tenda official website for firmware updates addressing the formSetCfm stack overflow. If the device is end-of-life or no patch is released, plan for replacement with a currently supported model.
Workarounds
- Place the Tenda W3 behind a network firewall that restricts access to its HTTP management interface
- Disable the web administration service when not actively configuring the device, if the firmware supports doing so
- Replace affected devices with hardware that receives active security maintenance from the vendor
# Example: restrict access to the router management interface using iptables on an upstream gateway
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -s <admin_workstation_ip> -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
