dbcve.org
Ios XrOperating system · Cisco

CVE-2023-20233

MEDIUM · 6.5 CVSS v3.1 Published 2023-09-13
Fix available
A fix is available. Upgrade to 7.5.4 / 7.6.3 or later.
See remediation →
72/100
Remediation priority · Elevated
Remotely reachable No privileges

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 Connectivity Fault Management (CFM) feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to incorrect processing of invalid continuity check messages (CCMs). An attacker could exploit this vulnerability by sending crafted CCMs to an affected device. A successful exploit could allow the attacker to cause the CFM service to crash when a user displays information about maintenance end points (MEPs) for peer MEPs on an affected device.

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 Connectivity Fault Management (CFM) feature allows an unauthenticated remote attacker to cause a denial of service by sending crafted invalid continuity check messages (CCMs). The CFM service crashes when a user displays information about maintenance endpoints (MEPs) for peer MEPs on the affected device.

MitigationApply the Cisco IOS XR software update that addresses this vulnerability when available. Until then, consider network segmentation or ACLs to limit exposure to CFM-facing network segments.

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 XrOperating system
Affected:< 7.5.4>= 7.6, < 7.6.3>= 7.7, < 7.7.21>= 7.8, < 7.8.2= 7.9.0

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
Required
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/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 the device OS and version
    Run 'show version' or 'cat /proc/version' (if accessible via shell) to confirm the device runs Cisco IOS XR and note the exact version number
    Affected if The version falls within any of these ranges: < 7.5.4, >= 7.6 and < 7.6.3, >= 7.7 and < 7.7.2, >= 7.8 and < 7.8.2, or equals 7.9.0
  2. Confirm CFM feature is enabled
    Run 'show cfm configuration' or 'show ethernet cfm configuration' in IOS XR CLI to check if Connectivity Fault Management is configured on any interfaces
    Affected if CFM is enabled and actively processing continuity check messages on any interface or bridge domain
  3. Verify MEP configuration exists
    Run 'show cfm endpoints' or 'show ethernet cfm endpoints' to list any configured Maintenance Endpoints (MEPs) on the device
    Affected if Any MEPs are configured and active, as the crash occurs when displaying information about peer MEPs
  4. Check for recent CFM service crashes
    Run 'show logging' or 'show cfm statistics' to look for recent CFM process crashes or error messages related to CCM processing
    Affected if Recent CFM crashes or CCM-related errors appear in the logs

A device is affected if it runs a vulnerable IOS XR version AND has CFM enabled with active MEP configurations, as the crash only triggers when displaying peer MEP information while CFM is processing CCM messages.

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.

dbcve · scoped
Upgrade available Upgrade to 7.5.4 / 7.6.3 / 7.7.21 or later
Fixed in 7.5.47.6.37.7.21
Interim mitigation

Apply the Cisco IOS XR software update that addresses this vulnerability when available. Until then, consider network segmentation or ACLs to limit exposure to CFM-facing network segments.

Recommended fix High confidence

Upgrade to the latest release in your current version branch (7.5.4+, 7.6.3+, 7.7.21+, or 7.8.2+) or move to the most recent stable branch (7.9.x or later if available)

  1. 1. Identify the current Cisco IOS XR version running on the affected device using 'show version' command
  2. 2. Determine the appropriate target version based on the current branch: for 7.4.x or earlier go to 7.5.4+, for 7.6.x go to 7.6.3+, for 7.7.x go to 7.7.21+, for 7.8.x go to 7.8.2+
  3. 3. Download the corresponding Cisco IOS XR software update from the Cisco Software Download center
  4. 4. Back up the current device configuration using 'admin commit backup' or 'copy running-config startup-config'
  5. 5. Upload the new software image to the device's bootflash or harddisk
  6. 6. Set the boot variable to point to the new image using 'boot system bootflash:/<new-image-name>'
  7. 7. Reload the device with 'reload' command to apply the new software version
  8. 8. After reload, verify the new version is running with 'show version'
Caveat Software upgrade may introduce behavioral changes; test in lab environment first; some commands or outputs may have changed

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Ios Xr Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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Scan for this in your stack

Free · runs locally
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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-2023-20233 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
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data