Security readout for executives and security teams
Plain-English summary
This flaw can make an IPv6 access control list fail on affected Cisco routing or switching platforms. An outside attacker could reach resources the ACL was meant to block if crafted IPv6 traffic passes through the device. The provided sources rate it medium severity, not a confirmed active-exploitation emergency.
Executive priority
Treat this as a moderate network-control weakness. It is important for environments relying on Cisco IPv6 ACLs for segmentation, but the provided evidence does not show known active exploitation or critical service disruption.
Technical view
CVE-2021-1389 is an improper access-control issue in IPv6 traffic processing for Cisco IOS XR and Cisco NX-OS Software on certain devices. The CVSS 3.1 score is 5.8 with network attack vector, low complexity, no privileges, no user interaction, and limited integrity impact.
Likely exposure
Exposure is most likely where affected Cisco IOS XR or NX-OS devices route IPv6 traffic and enforce IPv6 interface ACLs. The provided bundle does not identify exact affected releases or device models.
Exploitation context
The source says an unauthenticated remote attacker could send crafted IPv6 packets through an affected device to bypass an interface ACL. CISA KEV status is false in the bundle, and no cited source here confirms active exploitation.
Researcher notes
Evidence is limited to the CVE metadata and Cisco advisory reference. Key missing details are exact affected releases, device models, fixed versions, and workarounds. Avoid broad claims beyond IOS XR, NX-OS, IPv6 traffic processing, and interface ACL bypass.
Mitigation direction
- Review the Cisco advisory for affected releases, device scope, and fixed software guidance.
- Inventory Cisco IOS XR and NX-OS devices enforcing IPv6 interface ACLs.
- Prioritize remediation where IPv6 ACLs protect sensitive internal resources.
- Do not rely solely on affected IPv6 interface ACLs until vendor guidance is applied.
Validation and detection
- Confirm whether Cisco IOS XR or NX-OS devices process IPv6 traffic on protected paths.
- Check for IPv6 ACLs configured directly on interfaces of those devices.
- Compare device software versions against Cisco advisory applicability guidance.
- Review network segmentation assumptions for resources protected only by those ACLs.
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-2021-1389 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
- 20210203 Cisco IOS XR and Cisco NX-OS Software IPv6 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.