CVE-2021-1377: Cisco IOS

Medium severity, CVSS 5.8. EPSS: 1.4% chance of exploitation in the next 30 days.

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.

Affected products

• Cisco IOS: version 12.2(6)i1 only; version 15.1(3)svr1 only; version 15.1(3)svr2 only; version 15.1(3)svr3 only; version 15.1(3)svs only; version 15.1(3)svs1 only; …
• Cisco IOS XE: version 3.6.6e only; version 3.6.7ae only; version 3.6.7be only; version 3.6.7e only; version 3.6.8e only; version 3.6.9ae only; …

Published 2021-03-24. Last modified 2026-06-17.