CVE-2021-1591Network attack vector

Unauthenticated ACL bypass via EtherChannel oversubscription

Published Aug 25, 2021 · Updated Nov 7, 2024

Improper access control in Cisco NX-OS Software on Nexus 9500 switches allows remote attackers to bypass port-channel ACL rules. The EtherChannel port subscription logic oversubscribes resources when ACLs are applied to port-channel interfaces, leaving protected traffic unenforced. Exploitation requires ACL-enabled port channels, and member-interface subinterfaces increase exposure; successful traffic reaches ACL-protected resources.

CVSS severity5.8
Medium
EPSS probability1.00%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper access control in Cisco NX-OS Software on Nexus 9500 switches allows remote attackers to bypass port-channel ACL rules. The EtherChannel port subscription logic oversubscribes resources when ACLs are applied to port-channel interfaces, leaving protected traffic unenforced. Exploitation requires ACL-enabled port channels, and member-interface subinterfaces increase exposure; successful traffic reaches ACL-protected resources.

The record

CVE
CVE-2021-1591
Published
Aug 25, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco NX-OS Software
Classifications
CWE-284
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 25, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 7, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=n/a

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco NX-OS Softwareversion=n/a

Published CVSS scores

5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
5.8Cisco Systems, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-284Improper Access Control

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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