CVE-2024-20465 in IOS
Summary
by MITRE • 09/25/2024
A vulnerability in the access control list (ACL) programming of Cisco IOS Software running on Cisco Industrial Ethernet 4000, 4010, and 5000 Series Switches could allow an unauthenticated, remote attacker to bypass a configured ACL.
This vulnerability is due to the incorrect handling of IPv4 ACLs on switched virtual interfaces when an administrator enables and disables Resilient Ethernet Protocol (REP). An attacker could exploit this vulnerability by attempting to send traffic through an affected device. A successful exploit could allow the attacker to bypass an ACL on the affected device.
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Analysis
by VulDB Data Team • 02/27/2025
This vulnerability exists within the access control list implementation of Cisco IOS Software on Industrial Ethernet 4000, 4010, and 5000 Series Switches, representing a critical weakness in network security enforcement. The flaw specifically manifests when administrators configure and subsequently enable or disable the Resilient Ethernet Protocol on switched virtual interfaces, creating a scenario where IPv4 ACLs fail to properly restrict traffic flow. This represents a fundamental failure in the software's security architecture, where legitimate access controls are circumvented without proper authentication or authorization mechanisms.
The technical exploitation of this vulnerability occurs through the improper handling of IPv4 access control lists within the switched virtual interface context when REP functionality is toggled. When an administrator enables or disables REP, the system fails to correctly maintain or reapply the configured ACL rules, allowing traffic that should be blocked to pass through the device unimpeded. This behavior stems from inadequate state management within the IOS software's packet filtering mechanisms, where the transition between REP enabled and disabled states does not properly reset or validate the ACL enforcement points. The vulnerability is classified as a weakness in access control mechanisms and aligns with CWE-284, which addresses improper access control implementations. Attackers can leverage this flaw by simply sending traffic through the affected device without requiring any authentication credentials, making it particularly dangerous for industrial network environments where physical access controls may be limited.
The operational impact of this vulnerability extends beyond simple network security breaches, as it fundamentally undermines the security posture of industrial networks that rely on these switches for critical infrastructure protection. In industrial settings, these switches often serve as gateways between different network segments, controlling access between operational technology and information technology systems. When ACLs are bypassed, attackers can potentially move laterally within the network, access sensitive industrial control systems, or disrupt critical operations. The remote nature of the exploit means that adversaries can target these switches from outside the network perimeter, eliminating the need for physical access or insider knowledge. This vulnerability particularly affects environments following industrial standards such as IEC 62443 and NIST SP 800-82, where network segmentation and access control are critical for maintaining operational technology security. The lack of authentication requirements for exploitation makes this a high-severity threat that could enable advanced persistent threats to establish footholds within industrial control networks.
Organizations should implement immediate mitigations including disabling REP functionality on affected switches when not required, applying the latest Cisco IOS software updates that address this specific vulnerability, and implementing additional network segmentation measures to limit the potential impact of successful exploitation. Network administrators should also conduct thorough audits of their access control policies and verify that ACL configurations remain effective even when REP is enabled. The vulnerability demonstrates the importance of comprehensive testing for security features during protocol state transitions, aligning with ATT&CK framework techniques related to privilege escalation and defense evasion. Organizations should also consider implementing network monitoring solutions that can detect anomalous traffic patterns that might indicate exploitation attempts, as the bypassed ACLs would not be properly logged or monitored by standard network security tools. This vulnerability highlights the critical need for security testing of industrial network equipment under various operational conditions, particularly when network protocols are enabled or disabled dynamically.