CVE-2021-1590: Cisco NX-OS Software system login block-for Denial of Service Vulnerability

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-08-25 · updated 2026-06-17
Weakness: CWE-787

Description

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: 7.0(3)i4(0.116), 7.3(7)n1(1b)
Cisco Unified Computing System (Managed): before 4.0\(4m\); from 4.1 before 4.1\(3d\) — fixed in 4.0\(4m\), 4.1\(3d\)

How to fix

Upgrade to a fixed version: Cisco Unified Computing System (Managed) 4.0\(4m\), 4.1\(3d\). Check the vendor advisory for mitigations.

References

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