No exploitation reported

CVE-2021-1523

No exploitation reported by the sources we read.

Published2021-08-25
WeaknessCWE-772

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

A vulnerability in Cisco Nexus 9000 Series Fabric Switches in Application Centric Infrastructure (ACI) Mode could allow an unauthenticated, remote attacker to cause a queue wedge on a leaf switch, which could result in critical control plane traffic to the device being dropped. This could result in one or more leaf switches being removed from the fabric. This vulnerability is due to mishandling of ingress TCP traffic to a specific port. An attacker could exploit this vulnerability by sending a stream of TCP packets to a specific port on a Switched Virtual Interface (SVI) configured on the device. A successful exploit could allow the attacker to cause a specific packet queue to queue network buffers but never process them, leading to an eventual queue wedge. This could cause control plane traffic to be dropped, resulting in a denial of service (DoS) condition where the leaf switches are unavailable. Note: This vulnerability requires a manual intervention to power-cycle the device to recover.

Timeline

dates in UTC

2021-08-2519:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-1523?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-1523?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Cisco nx-osversion to verify

Branch	Affected	Fixed in	Source
13.2	= 13.2\(3n\)	no fix published	NVD
14.2	= 14.2\(4i\)	no fix published	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Advisories and patches

tools.cisco.comVendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CISA-ADPSSVC decisionnone2024-11-07
OpenCVESSVC decisionnone—
CNACVSS 3.18.6read 2026-10-23
NVDCVSS 3.18.6read 2026-10-23
NVDCVSS 2.05read 2026-10-23
CNAweakness (CWE)CWE-772read 2026-10-23
NVDweakness (CWE)CWE-772read 2026-10-23
FIRST EPSSEPSS score1.3 %2026-10-23

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Published: 2021-08-25
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-1523?

Is CVE-2021-1523 actively exploited?

Active exploitation of CVE-2021-1523 has not been confirmed. Its EPSS score was 1.3% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-1523?

CVE-2021-1523 has a CVSS v3 base score of 8.6 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H.

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