Security readout for executives and security teams
Plain-English summary
This CVE affects Cisco Nexus 9500 switches where ACLs are applied to port channel interfaces. Under the described resource oversubscription condition, traffic that should be blocked by those ACLs may reach protected network resources. Treat it as a segmentation control failure, not a device takeover.
Executive priority
Schedule remediation as a medium-priority network segmentation risk. Raise urgency if affected switches protect regulated, production, or administrative networks where ACL bypass could undermine trust boundaries.
Technical view
Cisco describes an ACL bypass in NX-OS EtherChannel port subscription logic on Nexus 9500 Series switches. The issue is tied to oversubscription of resources when ACLs are applied to port channel interfaces. CVSS 3.1 is 5.8, network reachable, low complexity, unauthenticated, with low integrity impact and no stated confidentiality or availability impact.
Likely exposure
Exposure is most likely where Cisco Nexus 9500 switches enforce access restrictions using ACLs on port channel interfaces. The source bundle does not provide affected NX-OS version ranges, so teams must compare inventory against Cisco's advisory.
Exploitation context
The bundle does not show CISA KEV listing or other evidence of active exploitation. Cisco states exploitation would involve attempting to access network resources protected by the affected ACL, but no public exploit status is provided here.
Researcher notes
Evidence supports CWE-284 improper access control. Important gaps remain: the provided bundle does not include specific affected or fixed versions, workaround detail, or exploitation telemetry. Use the Cisco advisory as the authoritative source for product-specific remediation.
Mitigation direction
- Check Cisco's advisory for fixed NX-OS releases and supported workarounds.
- Inventory Cisco Nexus 9500 switches and their NX-OS versions.
- Identify ACLs applied to port channel interfaces.
- Prioritize remediation where these ACLs protect sensitive network segments.
- Retest ACL enforcement after vendor-recommended remediation.
Validation and detection
- Confirm whether Nexus 9500 devices use ACLs on port channel interfaces.
- Compare each NX-OS version against Cisco advisory guidance.
- Review segmentation designs that rely on affected port channel ACLs.
- Check whether compensating controls restrict access to protected resources.
- Document remediation status for every exposed switch.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-284: Authorization and privilege behavior lookup
Authorization weaknesses can support privilege escalation and valid-account review, depending on exploit path. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-1591 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N3.91.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.8MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- 20210825 Cisco Nexus 9500 Series Switches Access Control List Bypass VulnerabilityCVE reference · vendor-advisory, x_refsource_CISCO
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Access Control
Improper Access Control represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.