CVE-2020-3231 in Catalyst 2960-L
Summary
by MITRE
A vulnerability in the 802.1X feature of Cisco Catalyst 2960-L Series Switches and Cisco Catalyst CDB-8P Switches could allow an unauthenticated, adjacent attacker to forward broadcast traffic before being authenticated on the port. The vulnerability exists because broadcast traffic that is received on the 802.1X-enabled port is mishandled. An attacker could exploit this vulnerability by sending broadcast traffic on the port before being authenticated. A successful exploit could allow the attacker to send and receive broadcast traffic on the 802.1X-enabled port before authentication.
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Analysis
by VulDB Data Team • 10/21/2020
The vulnerability identified as CVE-2020-3231 represents a significant security flaw in Cisco's network infrastructure equipment, specifically affecting the Catalyst 2960-L Series Switches and Catalyst CDB-8P Switches. This weakness resides within the 802.1X authentication framework, which is designed to provide network access control by authenticating devices before granting them network access. The vulnerability stems from improper handling of broadcast traffic on ports that have 802.1X enabled, creating a window of opportunity for malicious actors to bypass authentication mechanisms. The flaw specifically impacts network security by allowing unauthorized access to broadcast communication channels that should remain restricted until proper authentication occurs.
The technical implementation of this vulnerability involves the mismanagement of broadcast packets within the switch's 802.1X processing logic. When a port is configured with 802.1X authentication enabled, the switch typically holds incoming traffic until the authentication process is complete. However, in affected Cisco switches, broadcast traffic is not properly filtered or held back during the authentication phase, allowing unauthorized packets to be forwarded immediately upon arrival. This behavior creates a race condition where an attacker can send broadcast packets before the authentication process completes, effectively bypassing the intended security controls. The vulnerability specifically affects the switch's ability to properly queue and process broadcast frames, enabling immediate forwarding of these packets regardless of the authentication status of the connecting device.
From an operational standpoint, this vulnerability poses a substantial risk to network security and compliance. An adjacent attacker who gains physical access to the network port can exploit this weakness to inject malicious broadcast traffic, potentially disrupting network operations or conducting reconnaissance activities. The ability to send and receive broadcast traffic before authentication creates opportunities for attackers to perform network mapping, discover network services, or even facilitate more sophisticated attacks such as man-in-the-middle scenarios. This vulnerability undermines the fundamental security principle of network access control, as it allows unauthorized network participation without proper authentication credentials. The impact extends beyond simple traffic interception, potentially enabling attackers to disrupt network availability and compromise the integrity of network communications.
The security implications of CVE-2020-3231 align with several ATT&CK framework techniques including T1046 Network Service Scanning and T1566 Phishing, as attackers can leverage the ability to send broadcast traffic to gather network information or deliver malicious payloads. The vulnerability also relates to CWE-284 Improper Access Control, specifically addressing inadequate privilege management in network switching equipment. Organizations should implement immediate mitigations including applying Cisco's security patches, disabling 802.1X on affected ports where possible, and implementing additional network segmentation controls. Network administrators should also consider deploying intrusion detection systems to monitor for unusual broadcast traffic patterns on authenticated ports. The vulnerability highlights the importance of proper input validation and access control implementation in network infrastructure devices, emphasizing that security controls must be robust even in environments where physical access is restricted. Organizations should also review their network access policies and consider implementing additional security layers beyond traditional 802.1X authentication to protect against such bypass vulnerabilities.