CVE-2018-0090 in NX-OS
Summary
by MITRE
A vulnerability in management interface access control list (ACL) configuration of Cisco NX-OS System Software could allow an unauthenticated, remote attacker to bypass configured ACLs on the management interface. This could allow traffic to be forwarded to the NX-OS CPU for processing, leading to high CPU utilization and a denial of service (DoS) condition. The vulnerability is due to a bad code fix in the 7.3.2 code train that could allow traffic to the management interface to be misclassified and not match the proper configured ACLs. An attacker could exploit this vulnerability by sending crafted traffic to the management interface. An exploit could allow the attacker to bypass the configured management interface ACLs and impact the CPU of the targeted device, resulting in a DoS condition. This vulnerability affects the following Cisco products running Cisco NX-OS System Software: Multilayer Director Switches, Nexus 2000 Series Switches, Nexus 3000 Series Switches, Nexus 5500 Platform Switches, Nexus 5600 Platform Switches, Nexus 6000 Series Switches, Nexus 7000 Series Switches, Nexus 7700 Series Switches, Nexus 9000 Series Switches in standalone NX-OS mode. Cisco Bug IDs: CSCvf31132.
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Analysis
by VulDB Data Team • 02/01/2021
This vulnerability resides within the management interface access control list configuration of Cisco NX-OS System Software, representing a critical flaw that undermines fundamental network security controls. The issue manifests as an authentication bypass condition that allows remote attackers to circumvent configured access restrictions without requiring valid credentials or prior access privileges. The vulnerability specifically targets the management interface of various Cisco network infrastructure devices, creating a pathway for unauthorized traffic to be processed by the NX-OS CPU. This represents a significant deviation from expected security behavior where properly configured ACLs should filter and control incoming traffic based on predefined rules. The flaw stems from an inadequate code fix implemented in the 7.3.2 code train, which introduced a regression that misclassifies traffic destined for the management interface, causing it to bypass the intended ACL filtering mechanisms.
The technical exploitation of this vulnerability occurs through the injection of crafted network traffic packets directly targeting the management interface of affected Cisco devices. This attack vector operates entirely outside the normal security boundaries that should protect management interfaces from unauthorized access. The misclassification of traffic packets results in improper routing decisions within the NX-OS software where packets intended for filtering by ACL rules are instead forwarded to the CPU for processing. This misdirection creates a scenario where legitimate security controls are bypassed, allowing malicious traffic to consume CPU resources without proper authorization checks. The vulnerability affects a broad range of Cisco networking equipment including multilayer directors, various Nexus series switches, and enterprise-grade network infrastructure, demonstrating the widespread impact of this code-level regression. The issue is categorized under CWE-284 which specifically addresses improper access control mechanisms, and aligns with ATT&CK technique T1072 for software deployment via remote services.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass significant denial of service conditions that can severely disrupt network operations. When exploited, the vulnerability causes sustained high CPU utilization on affected devices, potentially leading to complete service outages and network disruption. The malicious traffic consumes processing resources that should be dedicated to legitimate network functions, creating performance degradation that can cascade through the entire network infrastructure. Network administrators face the challenging scenario of defending against attacks that bypass traditional access control measures, requiring them to implement additional defensive measures or apply emergency patches. The vulnerability's remote exploitability means that attackers can target devices from outside the network perimeter without requiring physical access or network credentials, making it particularly dangerous in production environments where management interfaces are often exposed to external networks.
Mitigation strategies for this vulnerability require immediate implementation of security patches provided by Cisco, specifically addressing the code regression introduced in the 7.3.2 code train. Network administrators should prioritize updating affected devices to the latest software versions that contain the corrected ACL processing logic. Additional defensive measures include implementing network segmentation to isolate management interfaces from external networks, deploying additional monitoring systems to detect abnormal CPU utilization patterns, and configuring more restrictive firewall rules to limit access to management interfaces. The vulnerability highlights the importance of thorough regression testing during software updates and the potential risks associated with partial code fixes that may introduce new security weaknesses. Organizations should also consider implementing network access control lists that provide additional layers of protection beyond the default NX-OS ACL mechanisms, ensuring that even if the primary vulnerability is exploited, secondary controls can still provide protection. Regular security assessments and vulnerability scanning should be conducted to identify any remaining instances of the vulnerable code across the network infrastructure.