CVE-2021-44827 in Archer C20i
Summary
by MITRE • 03/05/2022
There is remote authenticated OS command injection on TP-Link Archer C20i 0.9.1 3.2 v003a.0 Build 170221 Rel.55462n devices vie the X_TP_ExternalIPv6Address HTTP parameter, allowing a remote attacker to run arbitrary commands on the router with root privileges.
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Analysis
by VulDB Data Team • 03/09/2022
The vulnerability CVE-2021-44827 represents a critical remote authenticated OS command injection flaw discovered in TP-Link Archer C20i routers running firmware versions 0.9.1 3.2 v003a.0 Build 170221 Rel.55462n and potentially other affected models. This vulnerability exists within the web interface of the router's HTTP server implementation, specifically targeting the X_TP_ExternalIPv6Address parameter which is used for managing external IPv6 address configurations. The flaw allows an authenticated attacker to inject malicious commands that are then executed with root privileges on the underlying operating system, effectively providing complete system compromise. The vulnerability stems from improper input validation and sanitization within the router's web application, creating a direct pathway for command execution through the HTTP interface.
The technical exploitation of this vulnerability occurs through the manipulation of the X_TP_ExternalIPv6Address HTTP parameter during authenticated web requests to the router's management interface. When the router processes this parameter, it fails to properly sanitize user input before incorporating it into system commands, creating a classic command injection vector. This flaw aligns with CWE-77 which categorizes command injection vulnerabilities, and specifically maps to the broader ATT&CK technique T1059.001 for command and script injection. The authenticated nature of the attack requires an attacker to first obtain valid credentials, typically through social engineering, credential reuse, or other initial compromise vectors, but once achieved, the attacker can execute arbitrary commands with the highest privileges available on the system.
The operational impact of this vulnerability is severe and far-reaching for any organization or individual utilizing affected TP-Link Archer C20i devices. Successful exploitation provides attackers with complete administrative control over the router, enabling them to modify network configurations, redirect traffic, establish persistent backdoors, and potentially use the compromised device as a pivot point for attacking internal network resources. The root privileges granted through this vulnerability mean that attackers can modify system files, install malware, disable security features, and gain access to all network traffic passing through the device. This compromise can lead to significant data breaches, man-in-the-middle attacks, and disruption of network services, particularly in environments where these devices serve as primary network gateways or firewalls.
Mitigation strategies for CVE-2021-44827 should prioritize immediate firmware updates from TP-Link, as the vendor has released patches addressing this specific vulnerability. Network administrators should also implement strict access controls and monitoring of router management interfaces, including disabling unnecessary services and restricting administrative access to trusted IP addresses only. The implementation of network segmentation and firewall rules can help limit the potential impact of such compromises by preventing lateral movement within the network. Additionally, regular security audits of network infrastructure should include verification of device firmware versions and patch management procedures to ensure all network devices remain protected against known vulnerabilities. Organizations should also consider implementing intrusion detection systems that can monitor for suspicious HTTP parameter manipulation patterns and establish incident response procedures specifically addressing router compromise scenarios.