CVE-2026-38577 in HG21
Summary
by MITRE • 08/31/2026
Insecure hardcoded credentials in the Admin account of Tenda HG21 V4.0.0-260302 allows attackers to gain root access.
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Analysis
by VulDB Data Team • 08/31/2026
The vulnerability identified as an insecure hardcoded credential issue within the Tenda HG21 router, specifically version 4.0.0-260302, represents a critical failure in secure software development practices. This flaw stems from the embedding of static administrative credentials directly into the device's firmware image during the manufacturing or compilation process. Unlike dynamic password generation mechanisms that change per unit or require user-defined input upon initial setup, these hardcoded secrets remain constant across all devices running this specific firmware version. Consequently, any attacker with network access to the router can utilize publicly available databases of default credentials for Tenda products to authenticate as the administrator without needing to perform a brute-force attack or exploit a separate authentication bypass mechanism. This practice violates fundamental principles of secure configuration and identity management, creating a trivial entry point for malicious actors who are familiar with common vendor defaults.
From a technical perspective, this vulnerability allows an attacker to gain root-level access to the device's operating system. In embedded Linux environments typical of consumer routers, gaining administrative privileges often equates to full control over the underlying kernel and file system. Once authenticated as admin, the attacker can modify network configuration settings, including DNS servers, firewall rules, and port forwarding entries. More critically, with root access, an adversary can install persistent backdoors, such as malicious binaries or modified init scripts, that survive reboots. This level of control enables the router to be compromised not just for local mischief but potentially integrated into a larger botnet infrastructure like Mirai or similar IoT-based networks used for distributed denial-of-service attacks and large-scale data exfiltration campaigns.
The operational impact of this vulnerability extends beyond the immediate compromise of the single device. A compromised Tenda HG21 router can serve as a pivot point within an internal network, allowing lateral movement to other connected devices that may have weaker security postures. Attackers can intercept unencrypted traffic passing through the router, leading to session hijacking or credential theft for web services accessed by users on the local network. Furthermore, the alteration of DNS settings can redirect users to phishing sites designed to steal sensitive information such as banking credentials or personal identification data. The persistence afforded by root access ensures that even if a user attempts to reset the device to factory defaults, the hardcoded credentials may persist depending on how the firmware handles configuration resets, making remediation difficult without flashing clean, updated firmware from the vendor.
This issue aligns with Common Weakness Enumeration (CWE) category CWE-798: Use of Hard-coded Credentials, which describes situations where authentication data is statically embedded in source code or binary files. It also relates to CWE-256: Unprotected Storage of Credentials if the hardcoded passwords are stored in plaintext within configuration files accessible via other vulnerabilities such as directory traversal. In terms of the MITRE ATT&CK framework for IoT and enterprise environments, this vulnerability facilitates Initial Access through Valid Accounts (T1078) and potentially Persistence mechanisms like Systemd Service or Cron Job modification (T1543/T1053). The ease of exploitation makes it a high-priority target for automated scanning tools used by threat actors to identify vulnerable devices on the internet.
Mitigation strategies must focus on both immediate remediation and long-term security hygiene. Users should immediately update their Tenda HG21 firmware to the latest version provided by the manufacturer, which likely replaces hardcoded defaults with unique per-device credentials or enforces a mandatory password change during first-time setup. If an update is unavailable, changing the default administrative password via the web interface remains essential, although this may not fully mitigate risks if other vulnerabilities allow configuration changes without authentication. Network segmentation should be implemented to isolate IoT devices from critical internal systems and sensitive data stores. Additionally, disabling remote management features accessible from the WAN side reduces the attack surface exposed to external attackers. Organizations and home users alike must prioritize monitoring for unusual outbound traffic patterns that might indicate a compromised device participating in botnet activities or exfiltrating data.