CVE-2026-90689 Overview
CVE-2026-90689 is a stack-based buffer overflow affecting Tenda W20E firmware version 15.11.0.61068_1546_841_CN_TDC. The flaw resides in the formDelWebAuthWhiteUser function, which processes the webAuthWhiteUserIndex argument without proper boundary validation. An attacker can manipulate this argument to overwrite adjacent stack memory. The vulnerability is exploitable remotely over the network and requires only low privileges. Successful exploitation can lead to arbitrary code execution or denial of service on the affected router. The weakness is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer).
Critical Impact
Remote attackers with low privileges can trigger a stack-based buffer overflow in the Tenda W20E web management interface, potentially achieving arbitrary code execution on the router.
Affected Products
- Tenda W20E router firmware 15.11.0.61068_1546_841_CN_TDC
- The vulnerable formDelWebAuthWhiteUser handler in the router web management interface
- Deployments exposing the router administration interface to untrusted networks
Discovery Timeline
- 2026-09-14 - CVE-2026-90689 published to the National Vulnerability Database
- 2026-09-14 - Last updated in NVD database
Technical Details for CVE-2026-90689
Vulnerability Analysis
The vulnerability exists in the formDelWebAuthWhiteUser function within the Tenda W20E router web management interface. This function handles the deletion of web authentication whitelist entries and accepts a user-supplied webAuthWhiteUserIndex parameter. The function copies the parameter into a fixed-size stack buffer without validating its length. When the input exceeds the buffer boundary, adjacent stack memory is overwritten, including the saved return address and stack frame pointers. This memory corruption can result in denial of service or, if the attacker crafts input carefully, arbitrary code execution in the context of the router process. Because the router web interface typically runs with elevated privileges, successful exploitation can grant full control of the device.
Root Cause
The root cause is the absence of bounds checking on the webAuthWhiteUserIndex argument before it is copied into a stack-allocated buffer. Tenda's firmware uses unsafe string handling routines that do not enforce destination buffer size limits. This pattern is common across the Tenda W-series and is characteristic of [CWE-119] memory boundary violations.
Attack Vector
An attacker delivers a crafted HTTP request to the router's web management endpoint that invokes formDelWebAuthWhiteUser with an oversized webAuthWhiteUserIndex value. The attacker requires authenticated access with low privileges, but no user interaction is needed. If the management interface is reachable from the WAN or from a compromised LAN host, the request can be sent remotely. See the GitHub Security Advisory and the VulDB Vulnerability Details for additional context.
No verified proof-of-concept code is available. Refer to the linked advisories for technical reproduction details.
Detection Methods for CVE-2026-90689
Indicators of Compromise
- Unusually long or malformed webAuthWhiteUserIndex parameter values in HTTP POST requests directed at the router administration interface
- Router reboots, watchdog resets, or web service crashes correlated with inbound administrative requests
- Unexpected outbound connections originating from the router following administrative access
- Modifications to router configuration or new administrative sessions from unfamiliar source addresses
Detection Strategies
- Inspect HTTP traffic to router management endpoints for oversized parameter values targeting formDelWebAuthWhiteUser
- Deploy network intrusion detection signatures that match long strings in the webAuthWhiteUserIndex field
- Correlate router availability events with recent inbound requests to identify potential exploitation attempts
- Monitor for authentication events on the router admin interface from atypical geolocations or IP ranges
Monitoring Recommendations
- Forward router syslog and web server access logs to a centralized log platform for review and retention
- Alert on repeated failed authentication attempts followed by successful login to the router management interface
- Track configuration change events on network edge devices as part of routine security monitoring
- Baseline normal administrative traffic patterns and alert on deviations in request size or frequency
How to Mitigate CVE-2026-90689
Immediate Actions Required
- Restrict access to the Tenda W20E web management interface to trusted internal management networks only
- Disable remote WAN-side administration if it is currently enabled on the router
- Rotate administrative credentials and enforce strong, unique passwords for all router accounts
- Segment the affected router from sensitive internal systems until a vendor patch is available
Patch Information
No vendor patch has been published in the referenced advisories at the time of NVD publication. Monitor the Tenda Official Website for firmware updates addressing CVE-2026-90689. Review the VulDB CVE Report for status updates on remediation.
Workarounds
- Place the router administration interface behind a firewall access control list that permits only specific management workstations
- Use a VPN or jump host for any remote administration rather than exposing the web interface directly
- Disable unused router services and features that expand the attack surface
- Consider replacing end-of-support router models with actively maintained hardware if no firmware fix is released
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
