CVE-2020-5795 in Archer A7
Summary
by MITRE • 11/06/2020
UNIX Symbolic Link (Symlink) Following in TP-Link Archer A7(US)_V5_200721 allows an authenticated admin user, with physical access and network access, to execute arbitrary code after plugging a crafted USB drive into the router.
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Analysis
by VulDB Data Team • 12/03/2020
The vulnerability CVE-2020-5795 represents a critical security flaw in TP-Link Archer A7(US)_V5_200721 routers that demonstrates a dangerous combination of privilege escalation and arbitrary code execution capabilities. This vulnerability specifically targets the router's handling of symbolic links during USB drive insertion processes, creating a pathway for authenticated administrative users to gain unauthorized system access through physical and network means. The flaw exploits the router's failure to properly validate symbolic link references when processing USB storage devices, allowing maliciously crafted file structures to be executed with elevated privileges.
The technical implementation of this vulnerability stems from improper input validation within the router's firmware when processing USB devices. When an authenticated administrator plugs in a specially crafted USB drive containing symbolic links, the system follows these links without adequate sanitization, potentially executing code from unexpected locations. This behavior aligns with CWE-377, which addresses insecure temporary file handling, and CWE-22, which covers improper limitation of a pathname to a restricted directory. The vulnerability operates at the intersection of privilege escalation and code execution, where the authenticated admin user's credentials provide the necessary access to manipulate the router's file system processing capabilities.
The operational impact of this vulnerability extends beyond simple code execution to encompass full system compromise capabilities. An attacker with physical access to the device can leverage this vulnerability to install persistent backdoors, modify system configurations, or exfiltrate sensitive data from the network. The requirement for both physical access and network access creates a unique attack vector that combines social engineering with technical exploitation, making it particularly dangerous in environments where physical security is compromised. The vulnerability can be exploited through a simple USB insertion event, making it difficult to detect and prevent through traditional network monitoring approaches.
Mitigation strategies for CVE-2020-5795 should focus on firmware updates from TP-Link, which address the symbolic link handling behavior through proper validation and sanitization of USB device content. Network administrators should implement strict physical security controls to prevent unauthorized access to router hardware, while also monitoring for unusual USB device insertion events. The ATT&CK framework categorizes this vulnerability under T1059 for command and scripting interpreter usage, as well as T1078 for valid accounts, since it requires administrative privileges to exploit effectively. Organizations should also consider implementing USB device whitelisting policies and network segmentation to limit the potential impact of such attacks. Regular firmware updates and security assessments remain essential for preventing exploitation of similar vulnerabilities in network infrastructure devices.