CVE-2026-36807: Tenda W15E Buffer Overflow DoS Vulnerability – Remediation Guide

Technical summary

The vulnerability exists in the formAddWebAuthUser function within the web interface of Tenda W15E v15.11.0.10. The webAuthUserPwd parameter fails to properly validate input length before copying data into a fixed-size buffer, resulting in a classic stack-based buffer overflow (CWE-120). The lack of input sanitization allows an unauthenticated remote attacker to send an oversized password parameter via HTTP POST, overwriting stack memory and causing process termination or system hang. The CVSS 3.1 vector reflects network-accessible exploitation with no privileges required, no user interaction, and a direct attack on availability.

Business impact

Affected Tenda W15E routers become intermittently or persistently unavailable when exploited, disrupting network connectivity for all devices relying on them. For small offices, remote locations, or distributed facilities using Tenda equipment as primary internet gateways, a successful attack results in complete loss of WAN access until manual device restart. Organizations cannot rely on affected routers for continuous service, and repeated attacks create operational burden and loss of productivity. The vulnerability requires no credentials, making it a low-barrier attack vector for competitors, disgruntled users, or opportunistic threat actors scanning public IP ranges.

Affected systems

Tenda W15E wireless router running firmware version 15.11.0.10 is confirmed vulnerable. Organizations should verify whether this model and firmware version are deployed in their network infrastructure. Tenda's product line includes numerous router models; the scope of this vulnerability is limited to the W15E at the specified version, though similar buffer overflow patterns may exist in related products. Check your device management systems and network inventory for W15E units and their current firmware levels.

Exploitability

This vulnerability is straightforward to exploit. An attacker requires only network access to the router's web management interface (typically HTTP on port 80 or HTTPS on port 443) and can trigger the overflow with a single HTTP request containing a malformed webAuthUserPwd parameter. No authentication is required, no user interaction is needed, and exploit complexity is low. The attack is repeatable and reliable. However, exploitation requires the attacker to reach the router's management interface, which may be restricted by network segmentation, firewall rules, or access control lists in some deployments. The vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities catalog, but the low barrier to exploitation means active scanning and attempts are likely.

Remediation

Update the Tenda W15E to a patched firmware version released after the vulnerability's publication. Verify the patched version number against Tenda's official security advisory and device support page before deployment. As an interim mitigation, restrict access to the router's web management interface by binding it to specific trusted IP addresses, disabling remote management (if enabled), and ensuring the device is not exposed directly to the internet. Deploy the router behind a firewall and limit management access to a protected administrative network segment. These measures reduce but do not eliminate risk while patched firmware is tested and deployed.

Patch guidance

Contact Tenda support or consult their official security advisory to identify the current patched firmware version for the W15E. Tenda typically distributes firmware updates through their device web interface (System Settings > Firmware Upgrade) or via their web support portal. Download the update only from official Tenda channels to avoid supply chain compromise. Before updating production routers, test the patched firmware in a lab or non-critical environment to ensure compatibility with your network configuration and upstream ISP settings. Schedule updates during a maintenance window to account for brief service interruption. Verify the firmware version post-update using the device web interface or CLI to confirm the patch was successfully applied.

Detection guidance

Monitor web server logs on affected Tenda W15E devices for POST requests to the formAddWebAuthUser endpoint with abnormally long or malformed webAuthUserPwd parameter values. Network intrusion detection systems can be tuned to flag HTTP requests with suspiciously large password fields in web authentication requests to Tenda device IP ranges. Watch for unexpected device reboots or service degradation correlated with web access attempts. If device logs are accessible, check for buffer overflow exceptions or memory protection violations coinciding with exploit attempts. Implement network segmentation to ensure management traffic to Tenda devices originates only from authorized administrative subnets, making unauthorized exploitation attempts more visible.

Why prioritize this

This vulnerability warrants immediate attention because it is remotely exploitable without authentication, has a high CVSS score (7.5), and directly impacts network availability. Organizations using Tenda W15E routers as core connectivity devices should prioritize patching. The low complexity of exploitation and the lack of KEV listing (indicating no widespread in-the-wild exploitation documented by CISA yet) suggests a narrow window to patch before opportunistic attacks increase. The business impact of router unavailability justifies accelerated deployment cycles even if the vulnerable firmware version is not universally deployed.

Risk score, explained

The CVSS 3.1 score of 7.5 (HIGH) reflects a remotely exploitable, unauthenticated attack vector (AV:N, PR:N) with low complexity (AC:L) that causes high impact on availability (A:H) with no impact on confidentiality or integrity. The severity is driven by the ease of access and execution combined with guaranteed denial of service. The score is not critical because the impact is limited to availability and does not affect the confidentiality or integrity of data on the device or network. The high rating still demands urgent remediation for affected deployments.

Frequently asked questions