Stack-Based Buffer Overflow in Tenda W20E Router

Executive Summary

CVE-2026-90689 is a stack-based buffer overflow vulnerability in the Tenda W20E router firmware version 15.11.0.61068. The flaw exists in the formDelWebAuthWhiteUser function where the webAuthWhiteUserIndex argument is manipulated to trigger an overflow. The issue arises because the function uses unbounded strncpy operations to copy attacker-controlled IPMacBindRule values into fixed 32-byte stack buffers without proper length validation.

This leads to memory corruption and crashes in the web management process when oversized data is provided. The vulnerability can be exploited remotely by sending specially crafted requests to the affected device.

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Detection Guidance

To detect this vulnerability, monitor network traffic for requests targeting the Tenda W20E router's formDelWebAuthWhiteUser handler. Look for unusually large values in the webAuthWhiteUserIndex parameter that could trigger a stack-based buffer overflow. Check router logs for crashes or memory corruption events in the web management process.

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Impact Analysis

This vulnerability allows remote attackers to execute arbitrary code on the affected Tenda W20E router. Successful exploitation could lead to complete device compromise, allowing attackers to take control of the router, intercept network traffic, or use it as a pivot point for further attacks within the network.

The impact includes potential denial of service due to crashes, unauthorized access to sensitive information, and the ability to modify router settings or configurations. Users with vulnerable devices should apply patches immediately if available.

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Compliance Impact

This vulnerability could lead to non-compliance with data protection regulations such as GDPR and HIPAA. If the router is used in environments handling personal or sensitive data, the compromise could result in unauthorized access to such data, violating confidentiality requirements.

Regulatory frameworks like GDPR require organizations to implement appropriate security measures to protect personal data. A compromised router could be considered a failure to meet these security obligations, potentially leading to legal penalties or fines.

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Mitigation Strategies

Immediately update the Tenda W20E router firmware to the latest patched version if available. If no patch exists, restrict access to the router's web management interface by disabling remote administration and blocking unnecessary ports. Monitor for unusual activity and consider isolating the device from critical network segments.

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