CVE-2025-9090 in AC20
Summary
by MITRE • 08/17/2025
A vulnerability was identified in Tenda AC20 16.03.08.12. Affected is the function websFormDefine of the file /goform/telnet of the component Telnet Service. The manipulation leads to command injection. It is possible to launch the attack remotely. The exploit has been disclosed to the public and may be used.
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Analysis
by VulDB Data Team • 08/21/2025
The vulnerability CVE-2025-9090 represents a critical command injection flaw in the Tenda AC20 router firmware version 16.03.08.12, specifically within the Telnet Service component. This issue resides in the websFormDefine function of the /goform/telnet file, which serves as a web interface form handler for telnet configuration parameters. The vulnerability stems from inadequate input validation and sanitization mechanisms that fail to properly filter user-supplied data before incorporating it into system commands. Security researchers have identified that this flaw allows remote attackers to execute arbitrary commands on the affected device, effectively granting them full administrative control over the router's operations.
The technical exploitation of this vulnerability follows a command injection pattern that aligns with CWE-77 and CWE-89, where attacker-controlled input is directly concatenated into command strings without proper escaping or sanitization. The websFormDefine function appears to process form data submitted through the web interface and subsequently passes this data to system-level commands that enable or disable telnet services. When an attacker crafts malicious input containing shell metacharacters such as semicolons, ampersands, or command substitution operators, these inputs are interpreted by the underlying shell and executed with the privileges of the web server process, typically running with elevated system permissions. This remote code execution capability enables attackers to establish persistent backdoors, modify network configurations, redirect traffic, or extract sensitive information from the device.
The operational impact of CVE-2025-9090 extends beyond simple remote code execution, as it fundamentally compromises the security posture of networks relying on affected Tenda AC20 devices. Attackers can leverage this vulnerability to create persistent access points within corporate or residential networks, potentially enabling lateral movement to connected devices and systems. The disclosure of public exploits increases the likelihood of automated attacks targeting vulnerable devices, particularly in environments where default credentials remain unchanged or where network segmentation is inadequate. This vulnerability directly maps to several ATT&CK techniques including T1059.001 Command and Scripting Interpreter, T1021.001 Remote Services, and T1566.001 Phishing, as attackers can use the compromised device as a foothold for broader network infiltration. The affected device's web interface provides an accessible attack surface that requires no specialized tools or local access, making it particularly dangerous for widespread deployment scenarios.
Mitigation strategies for CVE-2025-9090 should prioritize immediate firmware updates from Tenda, as the vendor has likely released patches addressing the input validation issues in the websFormDefine function. Network administrators must disable unnecessary services such as telnet and enable only SSH for remote management, while implementing strict firewall rules that restrict access to the device's web interface to trusted IP addresses only. Additional protective measures include changing default administrative credentials, monitoring network traffic for suspicious command execution patterns, and implementing intrusion detection systems that can identify exploitation attempts. Organizations should also consider network segmentation to limit the potential impact of a successful compromise, ensuring that even if one device is compromised, attackers cannot easily move laterally within the network infrastructure. The vulnerability demonstrates the importance of secure input handling practices and highlights the need for comprehensive security testing of web interfaces in network devices to prevent similar command injection flaws from being introduced in future releases.