CVE-2019-6487 in TL-WDR5620
Summary
by MITRE
TP-Link WDR Series devices through firmware v3 (such as TL-WDR5620 V3.0) are affected by command injection (after login) leading to remote code execution, because shell metacharacters can be included in the weather get_weather_observe citycode field.
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Analysis
by VulDB Data Team • 05/02/2020
The TP-Link WDR Series devices affected by CVE-2019-6487 represent a critical vulnerability in networking equipment that demonstrates the dangers of insufficient input validation in web interfaces. This vulnerability specifically impacts firmware versions through v3, including models such as the TL-WDR5620 V3.0, where the device's web management interface fails to properly sanitize user input before processing it in shell commands. The flaw exists within the weather get_weather_observe functionality where the citycode parameter is directly incorporated into shell execution contexts without adequate sanitization or escaping mechanisms.
The technical exploitation of this vulnerability occurs through command injection attacks that leverage shell metacharacters within the citycode field. When an attacker submits malicious input containing shell operators such as semicolons, ampersands, or backticks, these characters are interpreted by the underlying shell and executed as part of the command sequence. This allows attackers to inject arbitrary commands that execute with the privileges of the web server process, typically running with elevated permissions on the device. The vulnerability is particularly dangerous because it occurs after successful authentication, meaning that an attacker who has already gained access to the device's web interface can escalate their privileges to full system control.
From an operational impact perspective, this vulnerability enables remote code execution capabilities that can be leveraged for complete system compromise. Attackers can execute arbitrary commands on the affected devices, potentially leading to data exfiltration, network reconnaissance, or further lateral movement within the compromised network. The vulnerability is especially concerning for enterprise environments where these devices may serve as network gateways or routers, as they could provide attackers with persistent access points and potential entry vectors for broader network infiltration. The fact that this vulnerability exists in firmware versions through v3 indicates that it has been present for an extended period, potentially affecting numerous deployed devices without proper patching.
The vulnerability aligns with CWE-77 and CWE-94 categories from the Common Weakness Enumeration, specifically representing command injection and code injection weaknesses. From the MITRE ATT&CK framework perspective, this vulnerability maps to techniques such as T1059.001 (Command and Scripting Interpreter: PowerShell) and T1068 (Exploitation for Privilege Escalation), as it allows for the execution of arbitrary commands with elevated privileges. The attack chain typically involves initial access through web interface authentication, followed by exploitation of the command injection vulnerability to execute malicious payloads. Organizations should implement immediate mitigations including firmware updates to versions that properly sanitize input parameters, network segmentation to limit access to affected devices, and monitoring for unusual command execution patterns. Additionally, the vulnerability highlights the importance of input validation practices and the need for secure coding methodologies that prevent shell metacharacter injection in all user-facing interfaces.