CVE-2018-15372 in IOS XE
Summary
by MITRE
A vulnerability in the MACsec Key Agreement (MKA) using Extensible Authentication Protocol-Transport Layer Security (EAP-TLS) functionality of Cisco IOS XE Software could allow an unauthenticated, adjacent attacker to bypass authentication and pass traffic through a Layer 3 interface of an affected device. The vulnerability is due to a logic error in the affected software. An attacker could exploit this vulnerability by connecting to and passing traffic through a Layer 3 interface of an affected device, if the interface is configured for MACsec MKA using EAP-TLS and is running in access-session closed mode. A successful exploit could allow the attacker to bypass 802.1x network access controls and gain access to the network.
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Analysis
by VulDB Data Team • 03/30/2020
The vulnerability identified as CVE-2018-15372 represents a critical security flaw in Cisco IOS XE Software's MACsec Key Agreement implementation that undermines fundamental network access control mechanisms. This issue specifically affects the Extensible Authentication Protocol-Transport Layer Security (EAP-TLS) functionality within the MACsec Key Agreement (MKA) process, creating a pathway for unauthorized network access through Layer 3 interfaces. The vulnerability stems from a logic error within the software implementation that fails to properly validate authentication states, allowing malicious actors to circumvent established security protocols. According to CWE-284, this represents an improper access control vulnerability where the system fails to properly enforce access restrictions, and aligns with ATT&CK technique T1078.1.1 which covers legitimate credentials usage through valid accounts. The flaw is particularly concerning because it operates at the network layer where traditional authentication mechanisms are expected to provide robust protection against unauthorized access attempts.
The technical exploitation of this vulnerability requires an attacker to be physically adjacent to the affected network device and to connect to a Layer 3 interface that has been configured with MACsec MKA using EAP-TLS authentication. The attack vector is specifically limited to adjacent network access due to the nature of MACsec protocols and their reliance on direct physical layer connections. When the affected interface operates in access-session closed mode, the flawed logic allows an unauthenticated attacker to establish a session that bypasses the normal 802.1x authentication process. This creates a condition where the network device incorrectly processes the authentication flow, failing to properly validate the identity of connecting devices. The vulnerability demonstrates a failure in the MKA state machine implementation where the system does not properly transition between authentication states, leading to an unintended operational mode where traffic can pass through without proper authentication verification.
The operational impact of this vulnerability extends far beyond simple network access bypass, as it fundamentally compromises the security posture of networks relying on 802.1x authentication mechanisms. An attacker who successfully exploits this vulnerability can effectively gain unrestricted access to the network segment connected through the compromised Layer 3 interface, potentially enabling lateral movement and privilege escalation attacks. The bypass of 802.1x network access controls creates a persistent threat vector that could allow attackers to establish footholds within the network infrastructure, particularly in environments where MACsec is implemented for enhanced security. This vulnerability affects the core network infrastructure components that are designed to provide secure access control, making it a significant concern for enterprise networks that depend on these security mechanisms. The impact is amplified when considering that this vulnerability can be exploited without requiring any special privileges or sophisticated attack techniques, making it accessible to a broad range of threat actors.
Organizations affected by CVE-2018-15372 should prioritize immediate remediation through official Cisco software updates and patches that address the underlying logic error in the MACsec MKA implementation. Network administrators should conduct comprehensive inventory assessments to identify all affected devices running Cisco IOS XE Software with MACsec MKA configured in access-session closed mode. The mitigation strategy should include disabling MACsec MKA functionality on affected interfaces until proper patches are applied, and implementing additional network segmentation measures to limit the potential impact of successful exploitation attempts. Security teams should also monitor network traffic for unusual patterns that might indicate exploitation attempts, particularly focusing on Layer 3 interface communications that bypass normal authentication procedures. According to industry best practices and the ATT&CK framework, organizations should implement network behavior monitoring solutions that can detect anomalous authentication flows and unauthorized access attempts. The vulnerability highlights the importance of maintaining up-to-date security patches and conducting regular security assessments to identify and remediate similar logic errors in network infrastructure software that could potentially compromise network access controls.