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Uncontrolled Resource ConsumptionWeakness · CWE-400

CVE-2025-20340

HIGH · 7.4 CVSS v3.1 Published 2025-09-10
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
79/100
Remediation priority · High
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 Address Resolution Protocol (ARP) implementation of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to trigger a broadcast storm, leading to a denial of service (DoS) condition on an affected device.  This vulnerability is due to how Cisco IOS XR Software processes a high, sustained rate of ARP traffic hitting the management interface. Under certain conditions, an attacker could exploit this vulnerability by sending an excessive amount of traffic to the management interface of an affected device, overwhelming its ARP processing capabilities. A successful exploit could result in degraded device performance, loss of management connectivity, and complete unresponsiveness of the system, leading to a DoS condition.

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 Cisco IOS XR Software's ARP implementation allows an unauthenticated, adjacent attacker to send excessive ARP traffic to the management interface, overwhelming ARP processing capabilities and triggering a broadcast storm. This results in degraded device performance, loss of management connectivity, and complete system unresponsiveness.

MitigationImplement rate limiting and ACLs on management interfaces, apply network segmentation to restrict adjacent attacker access, and apply Cisco patches when available.

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
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:A/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 running Cisco IOS XR Software
    Run 'show version' or 'show inventory' command to identify the operating system. Look for 'IOS XR' in the output.
    Affected if The device does not run Cisco IOS XR Software (this CVE only affects IOS XR)
  2. Identify the IOS XR version
    Execute 'show version' and locate the version string (e.g., 7.x.x, 6.x.x). Compare against the affected version range documented in the CVE advisory.
    Affected if The installed IOS XR version falls within the affected version range stated in the CVE (if versions are listed in official Cisco advisory)
  3. Verify management interface is configured
    Run 'show ip interface brief' or 'show interface MgmtEth0/RP0/CPU0/0' to check if the management interface is active. Also check 'show running-config interface MgmtEth' to see management interface configuration.
    Affected if The management interface (MgmtEth) is enabled and actively used for management traffic - this is the attack vector
  4. Check for ARP-related performance issues
    Run 'show processes cpu history' and 'show arp traffic' to examine ARP traffic patterns and CPU usage. Look for unusually high CPU utilization associated with ARP processes.
    Affected if CPU is abnormally high due to ARP processing, or ARP traffic shows signs of excessive broadcast/ARP packets on management interface
  5. Inspect management interface access controls
    Run 'show access-lists' and check configuration for any rate-limiting or ACLs applied to the management interface (MgmtEth).
    Affected if No rate limiting or ACLs are configured on the management interface, leaving it exposed to excessive ARP traffic

A user is affected if the device runs a vulnerable version of Cisco IOS XR with the management interface enabled and exposed to adjacent attackers without ARP rate limiting or access controls.

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

Implement rate limiting and ACLs on management interfaces, apply network segmentation to restrict adjacent attacker access, and apply Cisco patches when available.

Have this fixed Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing6.0 h
  • Review / QA3.0 h
27.0 hours of engineering $4,800
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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-2025-20340 in production — separate from our analysis above.

No notes yet

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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
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