CVE-2026-36771 Overview
CVE-2026-36771 is a stack overflow vulnerability in the Shenzhen Tenda Technology Co., Ltd Tenda W3 Wireless Router firmware version v1.0.0.3(2204). The flaw resides in the wl_radio parameter of the formwrlSSIDset function. Attackers can send a crafted input over the network to trigger the overflow. Successful exploitation causes a Denial of Service (DoS) condition on the affected device. The vulnerability is classified under [CWE-121] Stack-based Buffer Overflow.
Critical Impact
Unauthenticated network attackers can crash the Tenda W3 router, disrupting wireless connectivity for all connected clients.
Affected Products
- Tenda W3 Wireless Router firmware v1.0.0.3(2204)
- Shenzhen Tenda Technology Co., Ltd consumer networking equipment
- Devices exposing the formwrlSSIDset web management endpoint
Discovery Timeline
- 2026-06-09 - CVE-2026-36771 published to the National Vulnerability Database (NVD)
- 2026-06-09 - Last updated in NVD database
Technical Details for CVE-2026-36771
Vulnerability Analysis
The vulnerability exists in the formwrlSSIDset function within the Tenda W3 router's web management interface. This function handles requests to configure wireless SSID parameters. The wl_radio parameter accepts user-supplied input without proper length validation before copying it into a fixed-size stack buffer. An attacker who submits an oversized value for wl_radio overflows the buffer and corrupts adjacent stack memory, including the saved return address. The router process crashes, terminating wireless service availability until the device is restarted.
Root Cause
The root cause is missing bounds checking on the wl_radio parameter inside formwrlSSIDset. The function uses an unsafe memory copy operation against a stack-allocated buffer of fixed size. Because the input length is attacker-controlled, the copy writes beyond the buffer boundary. This pattern matches [CWE-121] Stack-based Buffer Overflow and is common across consumer router firmware that reuses legacy C string handling without length-aware alternatives.
Attack Vector
The attack vector is network-based and requires no authentication or user interaction. An attacker reaches the management interface and submits a crafted HTTP request with an oversized wl_radio value to the formwrlSSIDset endpoint. The request triggers the overflow and crashes the service. Exposure of the router management interface to untrusted networks materially increases risk. A public proof-of-concept exists in the SemVulLLM GitHub Repository.
Detection Methods for CVE-2026-36771
Indicators of Compromise
- Unexpected reboots or crashes of the Tenda W3 router coinciding with HTTP POST requests to the formwrlSSIDset endpoint
- HTTP requests containing abnormally long wl_radio parameter values directed at the router management interface
- Loss of wireless connectivity for all clients without administrator-initiated configuration changes
Detection Strategies
- Inspect HTTP traffic to the router management interface for wl_radio parameter lengths exceeding expected boundaries (typically a handful of bytes for a boolean radio toggle)
- Correlate router availability loss events with preceding inbound HTTP requests to /goform/formwrlSSIDset
- Deploy network intrusion detection signatures matching oversized POST bodies targeting Tenda management endpoints
Monitoring Recommendations
- Monitor wireless infrastructure uptime and alert on repeated unscheduled reboots
- Log all administrative access to the router web interface and review for anomalous source addresses
- Track LAN/WAN exposure of the router management port and alert on changes
How to Mitigate CVE-2026-36771
Immediate Actions Required
- Restrict access to the Tenda W3 web management interface to trusted internal management hosts only
- Disable remote WAN-side management on the affected router
- Replace devices with vendor-supported alternatives if no firmware update is available
Patch Information
No vendor patch has been published in the available CVE data at the time of NVD publication on 2026-06-09. Administrators should monitor Shenzhen Tenda Technology for firmware updates addressing the formwrlSSIDset stack overflow.
Workarounds
- Place the router behind a perimeter firewall that filters inbound HTTP requests to the management interface
- Segment IoT and management traffic onto a dedicated VLAN with access control lists restricting reachability
- Apply network-layer rate limiting to inbound requests targeting the router administrative endpoints
# Example firewall rule to restrict router admin access to a trusted host
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.10 -j ACCEPT
iptables -A INPUT -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.
