How severe is CVE-2021-1387?

CVE-2021-1387 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-1387 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (69th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-1387?

CVE-2021-1387 primarily affects Cisco Unified Computing System. In total, 240 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-1387?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-1387 published?

CVE-2021-1387 was published on 2021-02-24 and last updated on 2026-06-17.

CVE-2021-1387

CVE-2021-1387 is a high-severity vulnerability in Cisco Unified Computing System with a CVSS 3.x base score of 8.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-401.

Key facts

Severity: High (CVSS 3.x base score 8.6)
CVSS v2: 4.3
EPSS exploit prediction: 1% (69th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-401
Affected product: Cisco Unified Computing System
Published: 2021-02-24
Last modified: 2026-06-17

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.

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 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-1387 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (69th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-1387?: CVE-2021-1387 primarily affects Cisco Unified Computing System. In total, 240 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-1387?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-1387 published?: CVE-2021-1387 was published on 2021-02-24 and last updated on 2026-06-17.

References

https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-ipv6-netstack-edXPGV7K

Affected products (240)

cpe:2.3:a:cisco:unified_computing_system:*:*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(0\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(1\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(2\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(3\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(4\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(4\)n1\(1a\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(5\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(5\)n1\(1a\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(6\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(6\)n1\(2s\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(6\)n1\(3s\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(6\)n1\(4s\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(7\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(7\)n1\(1a\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(7\)n1\(1b\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(8\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.0\(8\)n1\(1a\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(0\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(0\)n1\(1a\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(0\)n1\(1b\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(1\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(1\)n1\(1a\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(2\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(2\)n1\(1a\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(3\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(3\)n1\(2\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(3\)n1\(2a\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(3\)n1\(3\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(3\)n1\(4\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(3\)n1\(5\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(4\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(4\)n1\(1a\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(4\)n1\(1c\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(4\)n1\(1d\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(5\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.1\(5\)n1\(1b\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.2\(0\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.2\(1\)n1\(1\):*:*:*:*:*:*:*
cpe:2.3:o:cisco:nx-os:7.3\(0\)n1\(1\):*:*:*:*:*:*:*

More vulnerabilities in Cisco Unified Computing System

CVE-2021-44228 — Critical (CVSS 10.0): Apache Log4j2 2.0-beta9 through 2.15.0 (excluding security releases 2.12.2, 2.12.3, and 2.3.1) JNDI features used in…
CVE-2015-6435 — Critical (CVSS 9.8): An unspecified CGI script in Cisco FX-OS before 1.1.2 on Firepower 9000 devices and Cisco Unified Computing System…
CVE-2021-1368 — High (CVSS 8.8): A vulnerability in the Unidirectional Link Detection (UDLD) feature of Cisco FXOS Software and Cisco NX-OS Software…
CVE-2019-1907 — High (CVSS 8.8): A vulnerability in the web server of Cisco Integrated Management Controller (IMC) could allow an authenticated, remote…
CVE-2019-1865 — High (CVSS 8.8): A vulnerability in the web-based management interface of Cisco Integrated Management Controller (IMC) Software could…
CVE-2019-1864 — High (CVSS 8.8): A vulnerability in the web-based management interface of Cisco Integrated Management Controller (IMC) Software could…

All CVEs affecting Cisco Unified Computing System →

Other CWE-401 (Missing Release of Memory after Effective Lifetime) vulnerabilities

CVE-2022-0742 — Critical (CVSS 9.1): Memory leak in icmp6 implementation in Linux Kernel 5.13+ allows a remote attacker to DoS a host by making it go…
CVE-2024-25450 — High (CVSS 8.8): imlib2 v1.9.1 was discovered to mishandle memory allocation in the function init_imlib_fonts().
CVE-2023-33718 — High (CVSS 8.8): mp4v2 v2.1.3 was discovered to contain a memory leak via MP4File::ReadString() at mp4file_io.cpp
CVE-2021-40633 — High (CVSS 8.8): A memory leak (out-of-memory) in gif2rgb in util/gif2rgb.c in giflib 5.1.4 allows remote attackers trigger an out of…
CVE-2021-3492 — High (CVSS 8.8): Shiftfs, an out-of-tree stacking file system included in Ubuntu Linux kernels, did not properly handle faults occurring…
CVE-2019-17340 — High (CVSS 8.8): An issue was discovered in Xen through 4.11.x allowing x86 guest OS users to cause a denial of service or gain…

Browse all CWE-401 (Missing Release of Memory after Effective Lifetime) vulnerabilities →