External risk intelligence

Tenda AC15 and AC5 Authentication Bypass and Command Injection Vulnerability.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2021-44971

This vulnerability affects Tenda home routers, which are network gateway devices commonly deployed at the edge of networks. While these management interfaces are intended for internal use, they are frequently misconfigured or exposed to the public internet, making them a common target for internet-based discovery and access.

Command Injection

Tenda Ac15 Firmware

15.03.05.20_multi15.03.06.48_multi

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This critical vulnerability affects Tenda networking devices, allowing unauthenticated attackers to bypass security controls, potentially leading to unauthorized access to sensitive information and even full system compromise. The concern is that these devices are often deployed at network perimeters, increasing the risk of external exploitation.

Attackers can bypass device security without credentials.
It affects widely used network gateway devices.
Confirm relevance and potential exposure.

Attack Path

How an attacker could exploit the issue

An attacker could gain access to vulnerable Tenda devices over the network without needing any credentials. This exposure allows for sensitive information to be stolen, and in some cases, can be combined with command injection to achieve remote code execution.

No authentication required for access.
Bypasses authentication to reach vulnerable component.
Leads to sensitive data exposure and RCE.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an unauthenticated attacker to bypass device authentication, potentially leading to unauthorized access to sensitive information and the execution of arbitrary commands. This could occur when devices are directly accessible from the internet.

Sensitive device information could be exposed.
Unauthenticated network access is possible.
System control could be compromised.

Operational Fix

Recommended remediation, mitigation, and detection steps

Tenda device owners, potentially including home users or small business network administrators, should prioritize identifying all deployed Tenda devices and assessing their internet exposure. The immediate first step is to confirm which devices are reachable from the internet and then determine the accountable owner for remediation. A risk-based approach to planning the necessary actions, such as firmware updates or device replacement, should follow this initial assessment.

Own by device or network administrator.
Verify internet-facing devices first.
Plan secure firmware updates.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

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Frequently asked questions

What is the Tenda AC15 or AC5 series?

These are wireless networking devices, specifically home routers, that function as gateway equipment to manage local network traffic and provide internet connectivity. They are commonly found in residential or small office environments to bridge the connection between an internet service provider and local devices like computers and phones.

What is the weakness in CVE-2021-44971?

The vulnerability is categorized as CWE-697, which involves an insufficient comparison of data. In the context of CVE-2021-44971, this flaw manifests as an authentication bypass. It means the system fails to correctly verify the credentials of a user, allowing an attacker to navigate past the login screen and interact with device settings as if they were an authorized administrator.

How does an attacker trigger this vulnerability?

An attacker triggers this flaw by sending specific network requests that exploit the bypass mechanism without providing a username or password. Crucially, the vulnerability does not require the attacker to have any existing user account or prior session on the device. Simply reaching the device's management interface over the network is sufficient to initiate the bypass.

Is my device at risk if it is not on the internet?

Halo Surface Signal identifies that while these management interfaces are designed for internal use, they are often inadvertently reachable from the public internet. If your device is configured to allow management access from the WAN side, the risk is significantly higher. Devices isolated entirely within a local network are still vulnerable to anyone with access to that local network, but they are not subject to automated internet-based scanning.

What steps should I take if I use these routers?

Begin by auditing your network to identify if any Tenda AC15 or AC5 devices are currently deployed. For each device, verify whether the administrative interface is accessible from outside your local network. Prioritize restricting access to these interfaces and look for official firmware updates provided by the manufacturer to address the underlying authentication failure.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.