CVE-2026-36806 Overview
CVE-2026-36806 is a stack-based buffer overflow [CWE-121] affecting Shenzhen Tenda Technology Co., Ltd Tenda W15E firmware version v15.11.0.10. The flaw resides in the formModifyWebAuthUser function, where the webAuthUserPwd parameter is copied into a fixed-size stack buffer without proper bounds checking. A remote, unauthenticated attacker can send a crafted HTTP request to trigger the overflow and cause a denial of service on the affected router.
Critical Impact
Remote unauthenticated attackers can crash the Tenda W15E router via a single malformed HTTP request, disrupting network connectivity for all downstream users.
Affected Products
- Shenzhen Tenda Technology Co., Ltd Tenda W15E
- Firmware version v15.11.0.10
- formModifyWebAuthUser web management function
Discovery Timeline
- 2026-06-09 - CVE-2026-36806 published to NVD
- 2026-06-10 - Last updated in NVD database
Technical Details for CVE-2026-36806
Vulnerability Analysis
The vulnerability is a stack-based buffer overflow in the formModifyWebAuthUser handler exposed by the Tenda W15E web administration interface. When the device processes an HTTP request targeting this endpoint, the handler reads the webAuthUserPwd parameter directly from the request and copies it into a fixed-size local buffer. The copy operation lacks length validation, so an attacker-controlled string longer than the destination buffer overwrites adjacent stack memory, including the saved return address.
On embedded MIPS or ARM router platforms, corrupting the stack typically causes the httpd process to crash. The crash terminates the web management interface and, depending on watchdog behavior, can cascade into a full device reboot or hang. The attack requires no authentication and no user interaction.
Root Cause
The root cause is missing input length validation on the webAuthUserPwd HTTP parameter before it is written to a stack buffer. This is a classic CWE-121 stack-based buffer overflow pattern frequently seen across Tenda consumer and small business router firmware, where strcpy-style operations are used without bounds enforcement.
Attack Vector
An attacker on the same network as the router web interface, or on the internet if the management interface is exposed, sends a crafted HTTP POST request to the URL handler bound to formModifyWebAuthUser. The request includes an oversized webAuthUserPwd field. Processing the request overwrites the saved return address on the stack, causing the httpd service to crash and denying administrative and routing services to legitimate users. Proof-of-concept details are available in the GitHub PoC Repository.
Detection Methods for CVE-2026-36806
Indicators of Compromise
- Unexpected reboots or crashes of the Tenda W15E httpd process and loss of web administration access.
- HTTP POST requests to endpoints invoking formModifyWebAuthUser containing abnormally long webAuthUserPwd parameter values.
- Source IPs sending repeated malformed authentication-modification requests to the router management interface.
Detection Strategies
- Inspect HTTP request bodies destined for the router management interface for webAuthUserPwd parameters exceeding typical password length boundaries.
- Deploy IDS/IPS signatures that match oversized parameter values in POST requests to Tenda formModifyWebAuthUser URIs.
- Correlate router availability loss with prior inbound HTTP traffic to the management interface to identify exploitation attempts.
Monitoring Recommendations
- Monitor uptime and reachability of Tenda W15E devices and alert on repeated unexpected restarts.
- Log all inbound connections to the router web management interface and review for unauthenticated external sources.
- Track HTTP request payload sizes targeting router admin endpoints and flag statistical outliers.
How to Mitigate CVE-2026-36806
Immediate Actions Required
- Restrict access to the Tenda W15E web management interface to trusted internal management VLANs only.
- Disable remote (WAN-side) administration on the device if it is currently enabled.
- Apply firewall rules upstream of the device to block untrusted sources from reaching TCP ports used by the router admin HTTP service.
Patch Information
No vendor advisory or firmware update for CVE-2026-36806 was referenced in the NVD entry at publication. Operators should monitor Shenzhen Tenda Technology for a firmware release addressing the formModifyWebAuthUser parameter handling and apply it as soon as it is available.
Workarounds
- Place the Tenda W15E behind a segmentation firewall and permit administrative HTTP traffic only from a dedicated management host.
- Change the device administrative port from defaults and limit it to allowlisted source addresses to reduce exposure to opportunistic scanning.
- If the device cannot be isolated, consider replacing it with a supported model until a fix is published, as the management interface is reachable without authentication for this attack.
# Example: restrict router admin interface to a single management host using iptables on an upstream gateway
iptables -A FORWARD -p tcp -d 192.0.2.10 --dport 80 -s 192.0.2.250 -j ACCEPT
iptables -A FORWARD -p tcp -d 192.0.2.10 --dport 80 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
