CVE-2021-1389 in IOS XR
Summary
by MITRE • 02/05/2021
A vulnerability in the IPv6 traffic processing of Cisco IOS XR Software and Cisco NX-OS Software for certain Cisco devices could allow an unauthenticated, remote attacker to bypass an IPv6 access control list (ACL) that is configured for an interface of an affected device. The vulnerability is due to improper processing of IPv6 traffic that is sent through an affected device. An attacker could exploit this vulnerability by sending crafted IPv6 packets that traverse the affected device. A successful exploit could allow the attacker to access resources that would typically be protected by the interface ACL.
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Analysis
by VulDB Data Team • 02/24/2021
This vulnerability resides in the IPv6 traffic processing mechanisms of Cisco IOS XR and NX-OS software implementations, representing a critical security flaw that undermines network access control policies. The vulnerability stems from improper handling of IPv6 packets within the forwarding plane of affected Cisco devices, specifically when these devices process traffic destined for interfaces with configured IPv6 access control lists. The flaw allows an unauthenticated remote attacker to bypass security controls that should normally restrict access to network resources through interface-based IPv6 ACLs.
The technical root cause of CVE-2021-1389 manifests as a failure in the IPv6 packet processing logic where the device does not properly validate or enforce the access control rules configured on interfaces. This misconfiguration occurs during the packet inspection phase when IPv6 traffic flows through the device's routing engine, allowing specially crafted packets to bypass the intended filtering mechanisms. The vulnerability is particularly concerning because it affects the fundamental packet processing capabilities of Cisco networking equipment, potentially enabling attackers to access protected network segments without proper authentication or authorization.
From an operational perspective, this vulnerability creates significant risk for organizations relying on IPv6 ACLs for network segmentation and access control. Attackers exploiting this flaw can gain unauthorized access to network resources that should be protected by interface-based IPv6 access control lists, potentially leading to lateral movement within networks, data exfiltration, or disruption of services. The remote nature of the exploit means that attackers can target vulnerable devices from outside the network perimeter without requiring any credentials or prior access. This vulnerability directly impacts the CIA triad by compromising confidentiality through unauthorized access to protected resources and potentially availability through service disruption.
Network administrators should implement immediate mitigations including disabling IPv6 functionality on affected interfaces where possible, implementing additional security controls such as IPv6 firewall rules at higher network layers, and monitoring for suspicious IPv6 traffic patterns. The vulnerability aligns with CWE-284 Access Control Issues and can be mapped to ATT&CK technique T1071.004 Application Layer Protocol: DNS, as attackers may leverage IPv6 traffic to bypass traditional network controls. Organizations should also consider implementing network segmentation strategies and deploying intrusion detection systems to monitor for exploitation attempts. Cisco has released software updates addressing this vulnerability, and administrators should prioritize applying these patches to maintain network security posture.
The broader implications of this vulnerability extend beyond immediate exploitation capabilities, as it demonstrates the complexity of IPv6 implementation in enterprise networking equipment and highlights the importance of thorough security testing for protocol handling mechanisms. Network security teams must recognize that IPv6 deployment introduces additional attack surfaces that require careful monitoring and validation of access control implementations. This vulnerability serves as a reminder of the critical need for continuous security assessment of network infrastructure components, particularly those handling protocol-specific traffic processing functions.