CVE-2021-1590: Cisco NX-OS

Medium severity, CVSS 5.3. EPSS: 1.4% chance of exploitation in the next 30 days.

A vulnerability in the implementation of the system login block-for command for Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a login process to unexpectedly restart, causing a denial of service (DoS) condition. This vulnerability is due to a logic error in the implementation of the system login block-for command when an attack is detected and acted upon. An attacker could exploit this vulnerability by performing a brute-force login attack on an affected device. A successful exploit could allow the attacker to cause a login process to reload, which could result in a delay during authentication to the affected device.

Affected products

• Cisco NX-OS: version 7.0(3)i4(0.116) only; version 7.3(7)n1(1b) only
• Cisco Unified Computing System: before 4.0\(4m\) (fixed in 4.0\(4m\)); from 4.1, before 4.1\(3d\) (fixed in 4.1\(3d\))

Published 2021-08-25. Last modified 2026-06-17.