CVE-2020-3174 in NX-OS
Summary
by MITRE
A vulnerability in the anycast gateway feature of Cisco NX-OS Software could allow an unauthenticated, adjacent attacker to cause a device to learn invalid Address Resolution Protocol (ARP) entries. The ARP entries are for nonlocal IP addresses for the subnet. The vulnerability is due to improper validation of a received gratuitous ARP (GARP) request. An attacker could exploit this vulnerability by sending a malicious GARP packet on the local subnet to cause the ARP table on the device to become corrupted. A successful exploit could allow the attacker to populate the ARP table with incorrect entries, which could lead to traffic disruptions.
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Analysis
by VulDB Data Team • 04/06/2024
The vulnerability identified as CVE-2020-3174 resides within Cisco NX-OS Software's anycast gateway feature, representing a critical security flaw that undermines network infrastructure integrity. This weakness specifically targets the Address Resolution Protocol implementation, which serves as the fundamental mechanism for mapping IP addresses to MAC addresses within local networks. The vulnerability manifests when the system fails to properly validate gratuitous ARP requests, which are unsolicited ARP messages typically used to announce IP address changes or to resolve conflicts between network devices. The flaw exists in the context of adjacent attackers who possess network access within the same local subnet, making the attack vector particularly concerning for environments where physical or logical network proximity can be achieved by malicious actors.
The technical implementation of this vulnerability stems from inadequate input validation within the ARP processing pipeline of Cisco network devices running NX-OS Software. When a malicious actor sends a crafted gratuitous ARP packet, the system does not properly verify the legitimacy of the IP address contained within the ARP request. This improper validation allows the device to accept and store invalid ARP entries in its ARP table, specifically for nonlocal IP addresses within the same subnet. The issue aligns with CWE-20, which describes improper input validation, and represents a classic case of insufficient sanitization of network protocol data. The vulnerability's exploitation requires minimal privileges since no authentication is required, making it particularly dangerous as it can be triggered by anyone with access to the local network segment.
The operational impact of CVE-2020-3174 extends beyond simple network disruption to potentially compromise the entire network routing infrastructure. When the ARP table becomes corrupted with invalid entries, network devices may begin forwarding traffic to incorrect MAC addresses, leading to packet loss, communication failures, and potential man-in-the-middle scenarios. The anycast gateway functionality, which is designed to provide high availability and load distribution across multiple network paths, becomes compromised as the system cannot reliably determine legitimate network endpoints. This vulnerability particularly affects enterprise networks where anycast implementations are common for services like virtual router redundancy protocol and load balancing solutions. The attack can result in significant service degradation or complete network outages, depending on the scale and sophistication of the malicious ARP flooding attempts. According to ATT&CK framework, this vulnerability maps to T1071.004 for Application Layer Protocol: DNS and T1566.001 for Phishing: Spearphishing Attachment, as it enables network-level attacks that can facilitate more sophisticated exploitation techniques.
Mitigation strategies for CVE-2020-3174 should focus on both immediate defensive measures and long-term architectural improvements. Network administrators should implement strict ARP inspection policies that validate ARP requests against known legitimate IP address ranges and MAC address bindings. The Cisco recommended solution involves upgrading to software versions that properly validate gratuitous ARP requests and implement proper ARP entry filtering mechanisms. Additional protective measures include configuring dynamic ARP inspection on switches, enabling port security features, and implementing network segmentation to limit the scope of potential attacks. Organizations should also consider deploying network monitoring solutions that can detect anomalous ARP activity patterns and automatically alert administrators to potential exploitation attempts. The vulnerability highlights the importance of network protocol validation and demonstrates how seemingly minor implementation flaws in core networking protocols can have cascading effects throughout enterprise infrastructure. Regular network audits and vulnerability assessments should include specific checks for ARP-related configurations, ensuring that all network devices properly implement security controls against malicious ARP manipulation.