CVE-2021-1377 in IOS
Summary
by MITRE • 03/25/2021
A vulnerability in Address Resolution Protocol (ARP) management of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to prevent an affected device from resolving ARP entries for legitimate hosts on the connected subnets. This vulnerability exists because ARP entries are mismanaged. An attacker could exploit this vulnerability by continuously sending traffic that results in incomplete ARP entries. A successful exploit could allow the attacker to cause ARP requests on the device to be unsuccessful for legitimate hosts, resulting in a denial of service (DoS) condition.
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Analysis
by VulDB Data Team • 04/04/2021
The vulnerability identified as CVE-2021-1377 represents a critical flaw in the Address Resolution Protocol management implementation within Cisco IOS and IOS XE software versions. This weakness specifically targets the handling of ARP entries within network devices, creating a pathway for remote attackers to disrupt normal network operations without requiring authentication credentials. The vulnerability stems from improper management of ARP cache entries, where the system fails to adequately process or maintain valid ARP mappings between IP addresses and MAC addresses. This flaw affects a broad range of Cisco networking equipment including routers and switches that operate on these software platforms, making it particularly concerning for enterprise network infrastructure.
The technical exploitation of CVE-2021-1377 occurs through continuous transmission of crafted network traffic designed to create incomplete ARP entries within the affected device's ARP table. When an attacker successfully leverages this vulnerability, they can flood the device with malicious ARP traffic that prevents the proper resolution of legitimate ARP requests. This mismanagement results in a cascading failure where legitimate network hosts on connected subnets cannot establish proper communication because their ARP entries become stale or invalid. The underlying cause aligns with CWE-129, which addresses improper handling of input boundaries, and specifically relates to improper input validation in network protocol implementations. The attack vector is particularly dangerous because it operates entirely at the network layer without requiring any authentication, making it accessible to anyone who can reach the affected device on the network.
The operational impact of a successful exploit creates significant disruption to network services and can result in complete denial of service conditions for affected network segments. When ARP resolution fails for legitimate hosts, network connectivity is severely impaired as devices cannot properly communicate with each other within the same subnet. This vulnerability particularly affects network availability and can cause cascading failures throughout connected networks, as downstream devices depend on proper ARP resolution for data transmission. The attack can be sustained over time, allowing attackers to maintain persistent disruption of network services and potentially causing extended outages that affect business operations. Organizations relying on Cisco network infrastructure for critical operations face substantial risk when this vulnerability remains unpatched, as it can be exploited by both malicious actors seeking to disrupt services and by automated attack tools designed to identify and exploit such weaknesses.
Mitigation strategies for CVE-2021-1377 should prioritize immediate deployment of Cisco's security patches and updates to address the ARP management flaw. Network administrators should implement rate limiting and access control measures to restrict the volume of ARP traffic that can be processed by affected devices, effectively reducing the impact of continuous attack traffic. The implementation of ARP inspection mechanisms and dynamic ARP entry validation can help detect and prevent malicious ARP traffic from overwhelming legitimate ARP operations. Organizations should also consider deploying network segmentation strategies to isolate affected devices and limit the potential scope of exploitation. According to ATT&CK framework category T1498, this vulnerability aligns with network denial of service tactics, while the exploitation technique maps to T1071.004 which covers application layer protocol usage. Regular network monitoring and anomaly detection should be enhanced to quickly identify unusual ARP traffic patterns that may indicate exploitation attempts, and security teams should maintain updated threat intelligence on similar ARP-based attacks to improve defensive measures.