CVE-2026-36819 Overview
CVE-2026-36819 is a stack-based buffer overflow [CWE-121] affecting Shenzhen Tenda Technology Co., Ltd Tenda W20E firmware version v15.11.0.6. The flaw resides in the fromSetDhcpRules function, where the bindMACAddr parameter is copied into a fixed-size stack buffer without proper bounds validation. A remote, unauthenticated attacker can send a crafted HTTP request to trigger memory corruption and cause a Denial of Service (DoS) condition on the affected router.
Critical Impact
Remote unauthenticated attackers can crash the Tenda W20E router by sending a single malformed HTTP request to the DHCP rules endpoint, disrupting network connectivity for all clients.
Affected Products
- Shenzhen Tenda Technology Co., Ltd Tenda W20E
- Firmware version v15.11.0.6
- fromSetDhcpRules HTTP request handler
Discovery Timeline
- 2026-06-09 - CVE-2026-36819 published to NVD
- 2026-06-09 - Last updated in NVD database
Technical Details for CVE-2026-36819
Vulnerability Analysis
The vulnerability is a stack-based buffer overflow in the fromSetDhcpRules function within the Tenda W20E web management interface. The function processes HTTP requests that configure DHCP binding rules. It reads the bindMACAddr parameter from user-supplied input and copies it into a fixed-size stack buffer using an unsafe string copy operation. The function does not validate the length of the input against the destination buffer size.
When an attacker submits an oversized bindMACAddr value, the copy operation writes past the buffer boundary and corrupts adjacent stack data, including the saved return address. On the W20E's MIPS-based architecture, this overflow reliably terminates the httpd process and forces a reboot of the device.
Root Cause
The root cause is missing input length validation in the fromSetDhcpRules handler. The function assumes the bindMACAddr parameter conforms to MAC address formatting constraints but performs no enforcement before copying data into a fixed stack buffer. This pattern is consistent with [CWE-121] Stack-based Buffer Overflow.
Attack Vector
The attack is network-reachable and requires no authentication or user interaction. An attacker sends a crafted HTTP POST request to the router's web management endpoint with an oversized bindMACAddr parameter value. The malformed request reaches the vulnerable function, overflows the stack buffer, and crashes the web server process. A proof-of-concept demonstrating the issue is published in the GitHub PoC Repository.
No verified exploitation code is reproduced here. Refer to the linked repository for technical details of the trigger payload.
Detection Methods for CVE-2026-36819
Indicators of Compromise
- Unexpected reboots or crashes of the Tenda W20E httpd process followed by loss of LAN connectivity.
- HTTP POST requests targeting the DHCP rules configuration endpoint containing abnormally long bindMACAddr parameter values.
- Inbound HTTP traffic to the router's management interface from untrusted networks or WAN-side sources.
Detection Strategies
- Inspect HTTP request bodies destined for the router management interface and alert on bindMACAddr values exceeding standard MAC address length (17 characters).
- Monitor for repeated TCP resets or connection failures to the router's web management port, which indicate httpd crashes.
- Correlate router unavailability events with preceding HTTP requests captured at the network perimeter.
Monitoring Recommendations
- Forward router syslog and crash events to a centralized log platform and alert on repeated service restarts.
- Capture network telemetry for traffic destined to embedded device management interfaces and flag malformed request patterns.
- Track availability of network infrastructure devices and trigger investigation when DoS-style outages recur.
How to Mitigate CVE-2026-36819
Immediate Actions Required
- Restrict access to the Tenda W20E web management interface to trusted administrative hosts only and disable WAN-side management.
- Place affected routers behind a network segment that filters untrusted HTTP traffic to the device.
- Monitor vendor channels for firmware updates that address the fromSetDhcpRules parameter handling.
Patch Information
At the time of publication, no vendor advisory or patched firmware release has been listed in the NVD entry for CVE-2026-36819. Operators should monitor Shenzhen Tenda Technology Co., Ltd. for an updated firmware release superseding v15.11.0.6 and apply it as soon as it becomes available.
Workarounds
- Disable remote HTTP administration on the router and require administration only from a wired LAN host.
- Apply firewall ACLs upstream of the router to block external HTTP and HTTPS traffic to the management interface.
- Replace end-of-support consumer routers with vendor-supported models if no firmware fix becomes available.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
