CVE-2026-36773 Overview
CVE-2026-36773 is a stack-based buffer overflow [CWE-121] in the Shenzhen Tenda Technology Co., Ltd Tenda W3 Wireless Router firmware version v1.0.0.3(2204). The flaw resides in the ask_to_reboot function, where the Go parameter is processed without proper bounds checking. An attacker on the adjacent network can submit a crafted input to corrupt the stack and crash the router process. Successful exploitation results in a Denial of Service (DoS) condition on the affected device. A proof-of-concept exists in a public GitHub repository, though no exploitation in the wild has been reported.
Critical Impact
Adjacent-network attackers can trigger a Denial of Service on Tenda W3 routers by sending a crafted Go parameter to the ask_to_reboot function, interrupting network connectivity for all downstream clients.
Affected Products
- Shenzhen Tenda Technology Co., Ltd Tenda W3 Wireless Router
- Firmware version v1.0.0.3(2204)
- Web management interface exposing the ask_to_reboot function
Discovery Timeline
- 2026-06-09 - CVE-2026-36773 published to NVD
- 2026-06-10 - Last updated in NVD database
Technical Details for CVE-2026-36773
Vulnerability Analysis
The vulnerability is a classic stack-based buffer overflow in the router's HTTP request handler. The ask_to_reboot function reads the Go parameter from a client-supplied request and copies it into a fixed-size stack buffer. The copy operation does not validate the length of the input before writing. When an attacker provides a Go value larger than the destination buffer, adjacent stack memory is overwritten. This corrupts saved registers and the return address, causing the process to crash.
The attack does not require authentication or user interaction. However, the attacker must be on the adjacent network, typically the same Wi-Fi segment or local LAN as the router. The impact is limited to availability — the device reboots or hangs until manually recovered. Confidentiality and integrity are not directly affected based on the published CVSS vector.
Root Cause
The root cause is missing input validation on the Go parameter inside the ask_to_reboot handler. The function relies on an unbounded string copy operation, consistent with the pattern described by [CWE-121: Stack-based Buffer Overflow]. Tenda routers commonly use strcpy or sprintf style routines on attacker-controlled HTTP parameters without enforcing a maximum length. This design pattern repeatedly produces overflow conditions across the vendor's product line.
Attack Vector
An attacker connected to the same wireless or wired network as the router sends an HTTP request to the device's management interface. The request invokes the ask_to_reboot endpoint with an oversized Go parameter. The malformed input overflows the stack buffer, corrupts control data, and crashes the HTTP server or the entire device. The router becomes unreachable until it is power-cycled or reboots automatically.
A proof-of-concept demonstrating the crash is published in the GitHub PoC repository. No verified exploit code is reproduced here.
Detection Methods for CVE-2026-36773
Indicators of Compromise
- Unexpected reboots or crashes of the Tenda W3 router without administrator action
- HTTP requests to the router management interface containing abnormally long Go parameter values targeting the ask_to_reboot endpoint
- Loss of LAN or Wi-Fi connectivity correlated with management-plane traffic from an internal host
Detection Strategies
- Inspect inbound HTTP traffic to the router's management interface for Go parameter values exceeding expected length thresholds.
- Monitor router syslog or remote logging for repeated watchdog reboots, segmentation faults, or HTTP daemon restarts.
- Correlate device unavailability events with adjacent-network host activity to identify a probable source client.
Monitoring Recommendations
- Forward router and network telemetry to a centralized analytics platform to correlate device crashes with suspicious management-plane requests.
- Alert on any host issuing requests to administrative endpoints such as ask_to_reboot from non-administrative network segments.
- Track the availability of consumer-grade network equipment as part of standard uptime monitoring to surface DoS conditions quickly.
How to Mitigate CVE-2026-36773
Immediate Actions Required
- Restrict access to the router's web management interface to a dedicated administrative VLAN or trusted host.
- Disable remote management and ensure the management interface is not exposed to guest Wi-Fi networks.
- Segment IoT and untrusted client devices away from the router's management subnet.
Patch Information
No vendor patch has been published in the available CVE references at the time of writing. Consult Shenzhen Tenda Technology Co., Ltd directly for firmware updates beyond v1.0.0.3(2204). If a fixed firmware version is not available, treat the device as end-of-support for production use and consider replacement with a vendor that actively maintains firmware.
Workarounds
- Place the Tenda W3 behind a separate firewall and block adjacent-network access to its management interface.
- Enforce strong network segmentation so only authorized administrative workstations can reach the router HTTP service.
- Disable any unused services on the router to reduce the attack surface exposed to adjacent clients.
- Replace the affected device with a supported router if the vendor does not release a firmware fix.
# Example: restrict management interface access on an upstream firewall
# Replace 192.0.2.10 with the administrative workstation IP
# Replace 192.0.2.1 with the router management IP
iptables -A FORWARD -s 192.0.2.10 -d 192.0.2.1 -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -d 192.0.2.1 -p tcp --dport 80 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
