CVE-2021-1591

mediumpriority · track · 21EPSS 0.010 · 63 %ileEURUUS

grimoire priorityP3 · Track

Exploitable?

—

no known exploitation

Likely / severe?

1.00% (63rd) EPSS

CVSS 5 · medium

Is it mine?

16 products

Check your exposure

Who says so?

5 sources

cnnvd · enisa_euvd · fstec_bdu · cisco_csaf

EPSS · scored 2026-10-26

A vulnerability in the EtherChannel port subscription logic of Cisco Nexus 9500 Series Switches could allow an unauthenticated, remote attacker to bypass access control list (ACL) rules that are configured on an affected device. This vulnerability is due to oversubscription of resources that occurs when applying ACLs to port channel interfaces. An attacker could exploit this vulnerability by attempting to access network resources that are protected by the ACL. A successful exploit could allow the attacker to access network resources that would be protected by the ACL that was applied on the port channel interface.

remediations

Vendor fix, mitigation, or workaround guidance, as published by each source.

A vendor fix is available.

FixedCisco NX-OS Software 10.1(1) when installed on Cisco Nexus 9000 Series Switchescisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
FixedCisco NX-OS Software 9.3(3) when installed on Cisco Nexus 9000 Series Switchescisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
FixedCisco NX-OS Software 9.3(4) when installed on Cisco Nexus 9000 Series Switchescisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
FixedCisco NX-OS Software 9.3(5) when installed on Cisco Nexus 9000 Series Switchescisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
FixedCisco NX-OS Software 9.3(5w) when installed on Cisco Nexus 9000 Series Switchescisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
FixedCisco NX-OS Software 9.3(6) when installed on Cisco Nexus 9000 Series Switchescisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
FixedCisco NX-OS Software 9.3(7) when installed on Cisco Nexus 9000 Series Switchescisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com
FixedCisco NX-OS Software 9.3(7k) when installed on Cisco Nexus 9000 Series Switchescisco_csaf
Cisco has released software updates that address this vulnerability.
https://software.cisco.com

cvss

Technical severity, 0–10. One row per scoring source.

5.8

010

base score 0–10 · higher = more severe · hover a vector to decode

v2.05mediumAV:N/AC:L/Au:N/C:N/I:P/A:Nprimary · NVD / NIST USexploitability 10 · impact 2.9

v3.15.3mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:Nprimary · NVD / NIST USexploitability 3.9 · impact 1.4

v3.15.8mediumAV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:Nsecondary · FSTEC (BDU) RU

v3.15.8mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:Nsecondary · ENISA EU

v3.15.8mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:Nsecondary · psirt@cisco.com USexploitability 3.9 · impact 1.4

v3.14.9mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:Usecondary · CVSS-BT (t0sche)

v3.15.8mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:Nsecondary · Cisco PSIRT US

ssvc

A stakeholder decision — act, attend, or track — from exploitation and impact.

Exploitation: none · Automatable: yes · Technical Impact: partialcoordinatorcisa_ssvcUS

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-284USCWE-284USCWE-287US

affected products (16)

Products and version ranges known to be affected.

Cisco NX-OS Software 10.1(1) when installed on Cisco Nexus 9000 Series Switchesall versionscisco_csafUS
Cisco NX-OS Software 9.3(3) when installed on Cisco Nexus 9000 Series Switchesall versionscisco_csafUS
Cisco NX-OS Software 9.3(4) when installed on Cisco Nexus 9000 Series Switchesall versionscisco_csafUS
Cisco NX-OS Software 9.3(5) when installed on Cisco Nexus 9000 Series Switchesall versionscisco_csafUS
Cisco NX-OS Software 9.3(5w) when installed on Cisco Nexus 9000 Series Switchesall versionscisco_csafUS
Cisco NX-OS Software 9.3(6) when installed on Cisco Nexus 9000 Series Switchesall versionscisco_csafUS
Cisco NX-OS Software 9.3(7) when installed on Cisco Nexus 9000 Series Switchesall versionscisco_csafUS
Cisco NX-OS Software 9.3(7k) when installed on Cisco Nexus 9000 Series Switchesall versionscisco_csafUS
Cisco Cisco NX-OS Software≤ n/aenisa_euvdEU
Cisco Systems Inc. NX-OS≤ 9.3(5w)fstec_bduRU
Cisco Systems Inc. NX-OS≤ 9.3(7k)fstec_bduRU
Cisco Systems Inc. NX-OS≤ 9.3(7)fstec_bduRU
Cisco Systems Inc. NX-OS≤ 10.1(1)fstec_bduRU
Cisco Systems Inc. NX-OS≤ 9.3(3)fstec_bduRU
Cisco Systems Inc. NX-OS9.3(4) → 9.3(6)fstec_bduRU
cisco nx-os= 9.3(4)nvdUScpe:2.3:o:cisco:nx-os:*:*:*:*:*:*:*:*

advisories (1)

Vendor and ecosystem advisories describing this.

cisco-sa-nexus-acl-vrvQYPVeCisco Nexus 9500 Series Switches Access Control List Bypass Vulnerability2021-08-25csaf · cisco_csafUS
A vulnerability in the EtherChannel port subscription logic of Cisco Nexus 9500 Series Switches could allow an unauthenticated, remote attacker to bypass access control list (ACL) rules that are configured on an affected device. This vulnerability is due to oversubscription of resources that occurs when applying ACLs to port channel interfaces. An attacker could exploit this vulnerability by attempting to access network resources that are protected by the ACL. A successful exploit could allow the attacker to access network resources that would be protected by the ACL that was applied on the port channel interface. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. This advisory is part of the August 2021 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: August 2021 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication ["https://sec.cloudapps.cisco.com/security/center/viewErp.x?alertId=ERP-74640"].

also known as (4)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd fstec_bdu cisco_csaf nvd NVD CVE.org MITRE

published 2021-08-25modified 2026-06-17

references (6)

External citations — patches, advisories, analysis.

scry

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