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Uncontrolled Resource ConsumptionWeakness · CWE-400

CVE-2026-20084

HIGH · 8.6 CVSS v3.1 Published 2026-03-25
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
95/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A vulnerability in the DHCP snooping feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause BOOTP packets to be forwarded between VLANs, resulting in a denial of service (DoS) condition. This vulnerability is due to improper handling of BOOTP packets on Cisco Catalyst 9000 Series Switches. An attacker could exploit this vulnerability by sending BOOTP request packets to an affected device. A successful exploit could allow an attacker to forward BOOTP packets from one VLAN to another, resulting in BOOTP VLAN leakage and potentially leading to high CPU utilization. This makes the device unreachable (either through console or remote management) and unable to forward traffic, resulting in a DoS condition. Note: This vulnerability can be exploited with either unicast or broadcast BOOTP packets. There are workarounds that address this vulnerability.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A vulnerability in the DHCP snooping feature of Cisco IOS XE Software on Catalyst 9000 Series Switches allows unauthenticated remote attackers to cause improper forwarding of BOOTP packets between VLANs. This BOOTP VLAN leakage results in high CPU utilization, making the device unreachable and unable to forward traffic, causing a denial of service condition.

MitigationApply Cisco-provided workarounds or patches for DHCP snooping to prevent BOOTP packet leakage between VLANs; verify DHCP snooping configuration blocks cross-VLAN BOOTP forwarding.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Confirm device is Catalyst 9000 Series Switch
    Run 'show version' or 'show inventory' to identify the device model and verify it is a Cisco Catalyst 9000 Series Switch running IOS XE software
    Affected if Device is not a Catalyst 9000 Series Switch running IOS XE - this vulnerability only affects that specific platform
  2. Check IOS XE version
    Run 'show version' to obtain the IOS XE software version, then compare it against the affected version range for CVE-2026-20084
    Affected if IOS XE version falls within the affected version range and DHCP snooping is enabled
  3. Verify DHCP snooping is enabled
    Run 'show ip dhcp snooping' to check if DHCP snooping is globally enabled, and run 'show ip dhcp snooping vlan' to check per-VLAN status
    Affected if DHCP snooping is enabled on any VLAN - the vulnerability requires DHCP snooping to be active
  4. Check for high CPU utilization
    Run 'show processes cpu history' or 'show processes cpu sorted' to monitor CPU usage; look for sustained high CPU utilization
    Affected if CPU utilization is abnormally high and DHCP snooping is enabled, potentially indicating BOOTP packet leakage
  5. Inspect for BOOTP VLAN leakage
    Run 'show ip dhcp snooping binding' and monitor BOOTP/DHCP traffic across VLANs using 'show ip dhcp snooping statistics' to identify unexpected cross-VLAN forwarding
    Affected if BOOTP packets are being forwarded between VLANs when they should be restricted, indicating the vulnerability is being exploited

A user is affected if they have a Catalyst 9000 Series Switch running IOS XE with DHCP snooping enabled and are experiencing BOOTP VLAN leakage or high CPU utilization from the DHCP snooping feature.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply Cisco-provided workarounds or patches for DHCP snooping to prevent BOOTP packet leakage between VLANs; verify DHCP snooping configuration blocks cross-VLAN BOOTP forwarding.

Have this fixed Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,980
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-20084 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data