CVE-2021-1387: A vulnerability in the network stack of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condit...

Description

A vulnerability in the network stack of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability exists because the software improperly releases resources when it processes certain IPv6 packets that are destined to an affected device. An attacker could exploit this vulnerability by sending multiple crafted IPv6 packets to an affected device. A successful exploit could cause the network stack to run out of available buffers, impairing operations of control plane and management plane protocols and resulting in a DoS condition. Manual intervention would be required to restore normal operations on the affected device. For more information about the impact of this vulnerability, see the Details section of this advisory.

Metrics

CVSS 3.1

8.6/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

EPSS Probability

1.37%

68.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-401

Affected Software

Vendor	Product	Versions
Cisco	Unified Computing System	>= 4.0, < 4.0\(4k\)
Cisco	Unified Computing System	>= 4.1, < 4.1\(1e\)
Cisco	Nx-Os	7.0\(0\)n1\(1\)
Cisco	Nx-Os	7.0\(1\)n1\(1\)
Cisco	Nx-Os	7.0\(2\)n1\(1\)
Cisco	Nx-Os	7.0\(3\)n1\(1\)
Cisco	Nx-Os	7.0\(4\)n1\(1\)
Cisco	Nx-Os	7.0\(4\)n1\(1a\)
Cisco	Nx-Os	7.0\(5\)n1\(1\)
Cisco	Nx-Os	7.0\(5\)n1\(1a\)
Cisco	Nx-Os	7.0\(6\)n1\(1\)
Cisco	Nx-Os	7.0\(6\)n1\(2s\)
Cisco	Nx-Os	7.0\(6\)n1\(3s\)
Cisco	Nx-Os	7.0\(6\)n1\(4s\)
Cisco	Nx-Os	7.0\(7\)n1\(1\)
Cisco	Nx-Os	7.0\(7\)n1\(1a\)
Cisco	Nx-Os	7.0\(7\)n1\(1b\)
Cisco	Nx-Os	7.0\(8\)n1\(1\)
Cisco	Nx-Os	7.0\(8\)n1\(1a\)
Cisco	Nx-Os	7.1\(0\)n1\(1\)
Cisco	Nx-Os	7.1\(0\)n1\(1a\)
Cisco	Nx-Os	7.1\(0\)n1\(1b\)
Cisco	Nx-Os	7.1\(1\)n1\(1\)
Cisco	Nx-Os	7.1\(1\)n1\(1a\)
Cisco	Nx-Os	7.1\(2\)n1\(1\)
Cisco	Nx-Os	7.1\(2\)n1\(1a\)
Cisco	Nx-Os	7.1\(3\)n1\(1\)
Cisco	Nx-Os	7.1\(3\)n1\(2\)
Cisco	Nx-Os	7.1\(3\)n1\(2a\)
Cisco	Nx-Os	7.1\(3\)n1\(3\)
Cisco	Nx-Os	7.1\(3\)n1\(4\)
Cisco	Nx-Os	7.1\(3\)n1\(5\)
Cisco	Nx-Os	7.1\(4\)n1\(1\)
Cisco	Nx-Os	7.1\(4\)n1\(1a\)
Cisco	Nx-Os	7.1\(4\)n1\(1c\)
Cisco	Nx-Os	7.1\(4\)n1\(1d\)
Cisco	Nx-Os	7.1\(5\)n1\(1\)
Cisco	Nx-Os	7.1\(5\)n1\(1b\)
Cisco	Nx-Os	7.2\(0\)n1\(1\)
Cisco	Nx-Os	7.2\(1\)n1\(1\)
Cisco	Nx-Os	7.3\(0\)n1\(1\)
Cisco	Nx-Os	7.3\(0\)n1\(1a\)
Cisco	Nx-Os	7.3\(0\)n1\(1b\)
Cisco	Nx-Os	7.3\(1\)n1\(1\)
Cisco	Nx-Os	7.3\(2\)n1\(1\)
Cisco	Nx-Os	7.3\(2\)n1\(1b\)
Cisco	Nx-Os	7.3\(2\)n1\(1c\)
Cisco	Nx-Os	7.3\(3\)n1\(1\)
Cisco	Nx-Os	7.3\(4\)n1\(1\)
Cisco	Nx-Os	7.3\(4\)n1\(1a\)

Showing 50 of 241 affected configurations. See NVD for the full list.

References

Timeline

Published: Feb 24, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-1387?

A vulnerability in the network stack of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability exists because the software improperly releases resources when it processes certain IPv6 packets that are destined to an affected device. An attacker could exploit this vulnerability by sending multiple crafted IPv6 packets to an affected device. A successful exploit could cause the network stack to run out of available buffers, impairing operations of control plane and management plane protocols and resulting in a DoS condition. Manual intervention would be required to restore normal operations on the affected device. For more information about the impact of this vulnerability, see the Details section of this advisory.

How severe is CVE-2021-1387?

CVE-2021-1387 has a CVSS score of 8.6/10 (HIGH severity). The EPSS model estimates a 1.37% probability of exploitation in the next 30 days.

How do I fix CVE-2021-1387?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.