CVE-2026-36813 Overview
CVE-2026-36813 is a stack-based buffer overflow [CWE-121] in the Tenda W15E router running firmware version v15.11.0.10. The flaw resides in the formCropAndSetWewifiPic function, where the picCropName parameter is copied into a fixed-size stack buffer without bounds checking. An unauthenticated remote attacker can submit a crafted HTTP request to trigger memory corruption and crash the device, producing a Denial of Service (DoS) condition.
Critical Impact
Unauthenticated attackers on the network can crash the Tenda W15E router by sending a single malformed HTTP request, disrupting connectivity for all downstream users.
Affected Products
- Shenzhen Tenda Technology Co., Ltd Tenda W15E
- Firmware version v15.11.0.10
- formCropAndSetWewifiPic web management handler
Discovery Timeline
- 2026-06-09 - CVE-2026-36813 published to NVD
- 2026-06-10 - Last updated in NVD database
Technical Details for CVE-2026-36813
Vulnerability Analysis
The vulnerability exists in the formCropAndSetWewifiPic function of the Tenda W15E web management interface. This handler processes HTTP requests related to cropping and setting the Wi-Fi picture asset. It reads the picCropName parameter from user-supplied HTTP input and writes it into a fixed-size buffer on the stack without validating the input length.
When the supplied value exceeds the destination buffer size, adjacent stack memory is overwritten. This corrupts saved registers and the function return address, causing the httpd process to crash. Because the device's web service is a single-process daemon, a crash interrupts router management and, depending on watchdog behavior, can disrupt LAN/WAN services until the device restarts.
The vulnerability is reachable over the network without authentication or user interaction, making it suitable for opportunistic DoS attacks against exposed management interfaces.
Root Cause
The root cause is missing length validation on the picCropName HTTP parameter before it is copied into a stack buffer. The function relies on unbounded string operations rather than length-checked alternatives, classifying the flaw as a stack-based buffer overflow [CWE-121].
Attack Vector
The attack vector is network-based. An attacker sends a crafted HTTP POST request to the vulnerable endpoint with an oversized picCropName parameter. No credentials are required. The result is a crash of the web management daemon and denial of service. See the GitHub PoC Repository for technical reproduction details.
Detection Methods for CVE-2026-36813
Indicators of Compromise
- HTTP requests to the Tenda W15E web interface containing abnormally long picCropName parameter values.
- Unexpected reboots or httpd process restarts on the affected router.
- Loss of web management availability following inbound HTTP traffic from untrusted sources.
Detection Strategies
- Inspect HTTP request bodies destined for the router management interface for picCropName values exceeding expected length thresholds.
- Deploy network IDS/IPS signatures that flag oversized POST parameters targeting Tenda form* endpoints.
- Correlate router availability dips with inbound HTTP traffic patterns from external or untrusted segments.
Monitoring Recommendations
- Forward router syslog and crash logs to a centralized logging platform for review of repeated httpd restarts.
- Monitor management interface uptime and alert on repeated availability loss.
- Track inbound HTTP traffic volume to router management ports from non-administrative source addresses.
How to Mitigate CVE-2026-36813
Immediate Actions Required
- Restrict access to the Tenda W15E web management interface to trusted internal administrative networks only.
- Disable remote (WAN-side) management on the affected device until a vendor patch is available.
- Place the router behind a network filter that drops oversized or malformed HTTP parameters targeting form* handlers.
Patch Information
No vendor patch is referenced in the NVD record at the time of publication. Administrators should monitor the Tenda support site for firmware updates addressing the formCropAndSetWewifiPic handler in W15E firmware v15.11.0.10. Until a patch is released, apply the workarounds below.
Workarounds
- Block external access to the router's HTTP management port at the network perimeter.
- Enforce ACLs allowing only known administrator IP addresses to reach the management interface.
- Replace end-of-life or unpatched Tenda W15E devices in high-availability environments where DoS resilience is required.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
