CVE-2001-0429 in CatOS
Summary
by MITRE
Cisco Catalyst 5000 series switches 6.1(2) and earlier will forward an 802.1x frame on a Spanning Tree Protocol (STP) blocked port, which causes a network storm and a denial of service.
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Analysis
by VulDB Data Team • 05/12/2019
The vulnerability identified as CVE-2001-0429 represents a critical flaw in Cisco Catalyst 5000 series switches running software versions 6.1(2) and earlier. This issue stems from the improper handling of 802.1x authentication frames within the switch's spanning tree protocol implementation. The fundamental problem occurs when the switch fails to properly enforce the STP port state restrictions, allowing authentication frames to traverse ports that should be logically blocked due to STP convergence processes. This behavior creates a dangerous condition where network traffic that should be contained within specific segments can propagate freely across the network topology.
The technical exploitation of this vulnerability occurs through the manipulation of 802.1x authentication frames that are typically used for network access control and port authentication. When these frames are forwarded across STP blocked ports, they create a feedback loop within the network infrastructure, where each switch port continuously forwards the authentication frames to neighboring switches. This creates an exponential growth in network traffic that rapidly consumes available bandwidth and processing resources. The vulnerability specifically affects the switch's ability to properly interpret and enforce STP port states, causing the system to treat blocked ports as if they were in a forwarding state for 802.1x traffic.
The operational impact of this vulnerability is severe and can result in complete network disruption through sustained denial of service conditions. Network storms generated by this vulnerability can cause switches to become unresponsive, leading to complete network outages that affect all users and services relying on the affected infrastructure. The storm effect occurs because each switch in the network continues to forward the 802.1x frames, creating a cascade effect that rapidly multiplies the original traffic volume. This can overwhelm network processing capabilities and cause switches to drop connections or become unavailable entirely. The vulnerability essentially allows an attacker to trigger a network-wide denial of service by simply initiating 802.1x authentication processes on a single port.
The vulnerability maps directly to CWE-1178, which addresses improper handling of spanning tree protocol frames, and aligns with ATT&CK technique T1499.004 for network denial of service attacks. Organizations affected by this vulnerability should implement immediate mitigations including upgrading to Cisco IOS software versions that address this specific issue, implementing port security measures to limit 802.1x frame propagation, and configuring STP to properly restrict frame forwarding. The recommended solution involves applying Cisco's security patches and updates that correct the STP frame handling behavior, ensuring that 802.1x frames are properly dropped on STP blocked ports. Network administrators should also consider implementing additional monitoring and alerting mechanisms to detect unusual traffic patterns that may indicate exploitation attempts, as well as establishing proper network segmentation strategies to limit the potential impact of such attacks.