CVE-2021-20149 in AC2600 TEW-827DRU
Summary
by MITRE • 12/31/2021
Trendnet AC2600 TEW-827DRU version 2.08B01 does not have sufficient access controls for the WAN interface. The default iptables ruleset for governing access to services on the device only apply to IPv4. All services running on the devices are accessible via the WAN interface via IPv6 by default.
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Analysis
by VulDB Data Team • 01/05/2022
This vulnerability affects Trendnet AC2600 TEW-827DRU routers running firmware version 2.08B01 and represents a critical access control flaw that undermines the device's network security posture. The vulnerability stems from an incomplete implementation of firewall rules that fails to account for IPv6 traffic, creating an unintended attack surface that exposes all router services to external network access. The device's default iptables configuration only applies security controls to IPv4 traffic while completely neglecting IPv6 traffic, which is a fundamental gap in network security implementation.
The technical flaw manifests as a missing firewall rule set that would normally restrict access to internal services from external WAN interfaces. In IPv4 environments, the device correctly implements iptables rules that prevent unauthorized access to services running on the router, but these rules are entirely absent for IPv6 traffic. This creates a scenario where all services that would normally be protected by firewall rules become accessible via the WAN interface through IPv6 connections, effectively bypassing the intended security architecture.
The operational impact of this vulnerability is severe and far-reaching, as it allows remote attackers to access all services running on the router without authentication or access control restrictions. This includes but is not limited to web management interfaces, SSH services, Telnet services, and any other network services that might be enabled on the device. The vulnerability is particularly dangerous because it affects all services simultaneously, providing attackers with comprehensive access to the router's functionality and potentially enabling further attacks on the internal network. From an attack perspective, this vulnerability directly aligns with the ATT&CK technique T1071.001 for application layer protocol usage and T1046 for network service scanning.
The root cause of this vulnerability can be categorized as a weakness in access control mechanisms, specifically related to incomplete firewall rule implementation. This aligns with CWE-284 which describes improper access control, and more specifically with CWE-1105 which addresses incomplete firewall rule sets. The vulnerability represents a classic case of security by obscurity failing, where the device assumes that IPv6 traffic will be handled appropriately by default, when in fact it requires explicit rule configuration that is missing in the implementation.
Organizations and individuals using affected Trendnet routers should immediately implement mitigations to address this vulnerability. The most effective immediate solution is to disable IPv6 functionality on the device if it is not required, as this would eliminate the attack surface entirely. Network administrators should also consider implementing additional network-level controls such as ingress and egress filtering to limit IPv6 traffic to only necessary services. The device firmware should be updated to a version that properly implements IPv6 firewall rules, or the device should be replaced if firmware updates are unavailable or insufficient.
This vulnerability demonstrates the importance of comprehensive security testing that includes all network protocols, particularly as IPv6 adoption increases across networks. The flaw highlights the need for security professionals to consider all network interfaces and protocols when implementing access control policies, as the presence of one protocol without proper controls for another can create significant security gaps. From a compliance perspective, this vulnerability would likely fail to meet requirements for network segmentation and access control as specified in standards such as NIST SP 800-53 and ISO 27001, making it a critical issue for organizations that must maintain regulatory compliance. The vulnerability also underscores the importance of proper network architecture design that accounts for all traffic flows and ensures that security controls are implemented consistently across all network protocols.