Security readout for executives and security teams
Plain-English summary
This flaw can let someone on an adjacent network disrupt a VLAN served by Cisco IOS XE wireless controller software. The impact is availability, not data theft. A crafted IPv6 packet can trigger a Layer 2 loop and cause traffic drops in that VLAN.
Executive priority
Treat this as a high-priority availability risk where affected controllers support important wireless or VLAN services. It is less likely to be internet-wide, but disruption inside the local network could be operationally significant.
Technical view
Cisco describes a logic error in processing specific link-local IPv6 traffic. An unauthenticated adjacent attacker can send a crafted IPv6 packet inbound through the wired interface of an affected controller, causing an L2 loop in a configured VLAN and a denial-of-service condition.
Likely exposure
Organizations using Cisco Catalyst 9800 Series or Catalyst 9000 Family wireless controllers with IOS XE Wireless Controller Software may be exposed. Exact affected versions are not included in the provided bundle.
Exploitation context
The CVSS vector requires adjacent network access and no privileges or user interaction. The bundle does not cite known active exploitation, and CISA KEV status is false.
Researcher notes
Key constraints are adjacent attack vector, crafted link-local IPv6 processing, and VLAN-scoped DoS through L2 loop behavior. The provided sources do not include exact affected versions, exploit maturity, or specific fixed releases.
Mitigation direction
- Review Cisco’s advisory for affected releases, fixed software, and any documented workarounds.
- Inventory Cisco IOS XE wireless controllers in Catalyst 9800 or Catalyst 9000 deployments.
- Prioritize upgrades or vendor-recommended remediation for controllers serving business-critical VLANs.
- Limit unnecessary adjacent Layer 2 access to controller wired interfaces where feasible.
- Monitor affected VLANs for traffic drops, loops, and instability until remediated.
Validation and detection
- Match controller models and IOS XE Wireless Controller Software versions against Cisco’s advisory.
- Confirm whether IPv6 traffic is enabled or reachable on relevant controller-connected VLANs.
- Review network telemetry for L2 loop indicators and unexplained VLAN traffic drops.
- Check change records to verify vendor-recommended fixes were applied.
- After remediation, monitor affected VLANs for recurring drops or loop events.
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
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CWE-670: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-34767 mapping review
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Open ATT&CK lookup- Severity
- High
- CVSS
- 7.4 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
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:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H2.84Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.4HighVector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20210922 Cisco IOS XE Software for Catalyst 9800 Series Wireless Controllers IPv6 Denial of Service 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.
Always-Incorrect Control Flow Implementation
Always-Incorrect Control Flow Implementation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.