CVE-2019-1977 in Nexus 9000
Summary
by MITRE
A vulnerability within the Endpoint Learning feature of Cisco Nexus 9000 Series Switches running in Application Centric Infrastructure (ACI) mode could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an endpoint device in certain circumstances. The vulnerability is due to improper endpoint learning when packets are received on a specific port from outside the ACI fabric and destined to an endpoint located on a border leaf when Disable Remote Endpoint Learning has been enabled. This can result in a Remote (XR) entry being created for the impacted endpoint that will become stale if the endpoint migrates to a different port or leaf switch. This results in traffic not reaching the impacted endpoint until the Remote entry can be relearned by another mechanism.
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Analysis
by VulDB Data Team • 12/11/2023
The vulnerability described in CVE-2019-1977 affects Cisco Nexus 9000 Series Switches operating in Application Centric Infrastructure (ACI) mode, specifically within the Endpoint Learning feature. This weakness represents a significant security concern as it enables unauthenticated remote attackers to induce denial of service conditions on endpoint devices without requiring any credentials or privileged access. The flaw manifests when packets are received on specific ports from external sources and are destined for endpoints located on border leaf switches, creating a critical operational weakness in the network infrastructure.
The technical root cause of this vulnerability stems from improper endpoint learning mechanisms when Disable Remote Endpoint Learning has been enabled on the switch configuration. When such conditions occur, the system creates a Remote (XR) entry for the affected endpoint that becomes stale upon endpoint migration to different ports or leaf switches. This stale entry prevents proper traffic routing and creates a persistent disruption in network communication. The vulnerability is classified under CWE-20: Improper Input Validation, as it involves incorrect handling of network packet processing and endpoint learning procedures within the ACI fabric.
The operational impact of this vulnerability extends beyond simple service disruption, as it fundamentally compromises the reliability and integrity of network communications within ACI environments. Network administrators face the challenge of maintaining consistent endpoint availability when remote attackers can exploit this weakness to create persistent stale entries that prevent proper traffic delivery. The DoS condition affects not just individual endpoints but can potentially cascade through the network fabric, impacting multiple devices and services that depend on proper endpoint learning mechanisms. This vulnerability particularly affects organizations relying on ACI for network virtualization and automation, where endpoint mobility is a critical feature.
Mitigation strategies for CVE-2019-1977 should focus on implementing proper network segmentation and access controls to limit external packet injection into the ACI fabric. Organizations should consider disabling the Disable Remote Endpoint Learning feature when it's not strictly required, or implementing additional monitoring to detect stale endpoint entries. Network administrators should also ensure that all Cisco Nexus 9000 Series switches are updated with the latest security patches provided by Cisco. The vulnerability aligns with ATT&CK technique T1499.004: Endpoint Denial of Service, which involves attacks targeting endpoint devices to prevent access to network resources. Regular network monitoring and endpoint learning validation procedures should be implemented to detect and remediate stale entries before they cause service disruption. Organizations should also consider implementing network access control policies that restrict external access to ACI fabric ports and validate all incoming packets against established security baselines to prevent exploitation of this remote attack vector.