CVE-2026-3841 in TL-MR6400
Summary
by MITRE • 03/12/2026
A command injection vulnerability has been identified in the Telnet command-line interface (CLI) of TP-Link TL-MR6400 v5.3. This issue is caused by insufficient sanitization of data processed during specific CLI operations. An authenticated attacker with elevated privileges may be able to execute arbitrary system commands. Successful exploitation may lead to full device compromise, including potential loss of confidentiality, integrity, and availability.
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Analysis
by VulDB Data Team • 03/12/2026
This vulnerability represents a critical command injection flaw in the Telnet CLI of TP-Link TL-MR6400 router firmware version 5.3. The issue stems from inadequate input sanitization mechanisms within the device's command processing pipeline, specifically when handling user-supplied data through the Telnet interface. The vulnerability falls under the CWE-77 category of Command Injection, which is classified as a high-severity weakness in the Common Weakness Enumeration framework. Attackers exploiting this flaw can leverage authenticated access to execute arbitrary system commands with the privileges of the Telnet service account, potentially leading to complete system compromise.
The technical implementation of this vulnerability occurs when the router's CLI processes user input without proper validation or escaping of special characters that could be interpreted by the underlying shell. This allows an attacker to inject malicious commands that bypass normal access controls and execute with elevated privileges. The exploitation requires authentication to the Telnet service, which typically means an attacker must first obtain valid credentials through social engineering, default credential exploitation, or other initial compromise techniques. Once authenticated, the attacker can craft specific command sequences that are processed directly by the system shell, enabling arbitrary code execution.
The operational impact of this vulnerability extends beyond simple command execution to encompass full system compromise. Successful exploitation can result in persistent backdoor access, data exfiltration, modification of network configurations, and potential use as a pivot point for attacking other devices within the network. The threat actor can leverage this vulnerability to establish persistent access, modify firewall rules, install malicious software, or use the compromised device as a launching point for lateral movement attacks. This aligns with the MITRE ATT&CK framework's techniques for privilege escalation and persistence, specifically covering T1059 for command and scripting interpreter and T1078 for valid accounts.
Mitigation strategies for this vulnerability should focus on immediate firmware updates from TP-Link, which would contain proper input validation and sanitization mechanisms. Network segmentation and access control measures should be implemented to limit Telnet access to trusted administrative workstations only. The principle of least privilege should be enforced by disabling unnecessary services, including Telnet, and using SSH instead. Additional protective measures include implementing strong authentication mechanisms, regular credential rotation, network monitoring for suspicious Telnet activity, and conducting regular vulnerability assessments of network infrastructure. Organizations should also consider implementing intrusion detection systems that can identify anomalous command execution patterns and establish incident response procedures for handling potential exploitation attempts.