dbcve.org
Ios XeOperating system · Cisco

CVE-2023-20027

HIGH · 8.6 CVSS v3.1 Published 2023-03-23
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 implementation of the IPv4 Virtual Fragmentation Reassembly (VFR) feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to improper reassembly of large packets that occurs when VFR is enabled on either a tunnel interface or on a physical interface that is configured with a maximum transmission unit (MTU) greater than 4,615 bytes. An attacker could exploit this vulnerability by sending fragmented packets through a VFR-enabled interface on an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in 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

This is a denial-of-service vulnerability in Cisco IOS XE's IPv4 Virtual Fragmentation Reassembly (VFR) feature. The flaw stems from improper handling of large packet reassembly when VFR is enabled on tunnel interfaces or physical interfaces with MTU exceeding 4,615 bytes. An attacker sending specifically crafted fragmented packets through an affected interface can trigger the device to reload.

MitigationDisable VFR on affected tunnel and physical interfaces, or reduce MTU to 4,615 bytes or less on physical interfaces. Apply Cisco's official patch when available.

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

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Ios XeOperating system
Affected:= 3.9.0as= 3.9.1s= 3.9.2s= 3.10.0s= 3.10.1s= 3.10.2as= 3.10.2s= 3.10.2ts= 3.10.3s= 3.10.4s= 3.10.5s= 3.10.6s

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. Identify IOS XE version
    Run 'show version' to display the installed IOS XE version
    Affected if The version matches one of: 3.9.0as, 3.9.1s, 3.9.2s, 3.10.0s, 3.10.1s, 3.10.2as, 3.10.2s, 3.10.2ts, 3.10.3s, 3.10.4s, 3.10.5s, or 3.10.6s
  2. Verify VFR feature status
    Run 'show vfr' or 'show vfr detail' to check if IPv4 Virtual Fragmentation Reassembly is enabled
    Affected if VFR is enabled and the device runs an affected IOS XE version
  3. Check for VFR on tunnel interfaces
    Run 'show vfr interface' to list all interfaces with VFR enabled and identify any tunnel interfaces in the output
    Affected if VFR is enabled on any tunnel interface and the device runs an affected version
  4. Check physical interface MTU with VFR
    Run 'show vfr interface' to find physical interfaces with VFR, then run 'show interface <name>' to check the MTU setting on each
    Affected if VFR is enabled on a physical interface with MTU exceeding 4,615 bytes

The device is affected if it runs an affected IOS XE version AND has VFR enabled on tunnel interfaces OR on physical interfaces with MTU greater than 4,615 bytes

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

Disable VFR on affected tunnel and physical interfaces, or reduce MTU to 4,615 bytes or less on physical interfaces. Apply Cisco's official patch when available.

Fix this in Ios Xe Scoped from the published advisory
  • Consultation3.0 h
  • Implementation3.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,100
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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-2023-20027 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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  • No spam, self-promotion, credentials, or personal data