dbcve.org
Ios XeOperating system · Cisco

CVE-2021-1624

HIGH · 8.6 CVSS v3.1 Published 2021-09-23
Fix available
A fix is available. Upgrade to after 17.3.3 or later.
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 Rate Limiting Network Address Translation (NAT) feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause high CPU utilization in the Cisco QuantumFlow Processor of an affected device, resulting in a denial of service (DoS) condition. This vulnerability is due to mishandling of the rate limiting feature within the QuantumFlow Processor. An attacker could exploit this vulnerability by sending large amounts of traffic that would be subject to NAT and rate limiting through an affected device. A successful exploit could allow the attacker to cause the QuantumFlow Processor utilization to reach 100 percent on the affected device, 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

A vulnerability in the Rate Limiting Network Address Translation (NAT) feature of Cisco IOS XE Software allows an unauthenticated remote attacker to cause 100% CPU utilization on the QuantumFlow Processor by sending large volumes of traffic subject to NAT and rate limiting, resulting in denial of service.

MitigationApply the Cisco IOS XE software update that addresses CVE-2021-1624; implement upstream traffic filtering or rate limiting as a temporary workaround until the patch can be deployed.

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:<= 17.3.3

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 the Cisco IOS XE version
    Run 'show version' or 'show version | include Version' to display the installed IOS XE version
    Affected if The version number displayed is 17.3.3 or lower (any version <= 17.3.3)
  2. Verify NAT is enabled on the device
    Run 'show ip nat translations' or 'show ip nat statistics' to check if NAT is actively configured
    Affected if NAT is enabled and actively translating traffic
  3. Check for rate limiting configuration on NAT interfaces
    Run 'show policy-map interface' or 'show running-config | include rate-limit' to see if rate limiting policies are applied to NAT-enabled interfaces
    Affected if Rate limiting or traffic policing policies are applied to interfaces using NAT
  4. Confirm QuantumFlow Processor usage
    Run 'show platform hardware qfp' or 'show platform hardware qfp status' to verify the QuantumFlow Processor is present and active
    Affected if The device has a QuantumFlow Processor and it is operational

The device is affected if it runs Cisco IOS XE version 17.3.3 or lower, has NAT enabled with rate limiting applied to NAT traffic, and utilizes a QuantumFlow Processor.

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 a release after 17.3.3
Interim mitigation

Apply the Cisco IOS XE software update that addresses CVE-2021-1624; implement upstream traffic filtering or rate limiting as a temporary workaround until the patch can be deployed.

Recommended fix Moderate confidence

Cisco IOS XE 17.4.1 or later stable release

  1. 1. Identify the current Cisco IOS XE version running on the affected device using 'show version' command
  2. 2. Schedule a maintenance window for the upgrade procedure
  3. 3. Download the fixed Cisco IOS XE software release (17.4.1 or later) from Cisco's software download center
  4. 4. Verify the software image integrity using the MD5/SHA256 checksum provided by Cisco
  5. 5. Back up the current device configuration
  6. 6. Upload the new IOS XE image to the device's flash storage
  7. 7. Configure the device to boot from the new image using 'boot system' command
  8. 8. Reload the device to apply the new image
Caveat Review Cisco release notes for 17.4.x for any command syntax changes or feature modifications that may affect your configuration

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

Fix this in Ios Xe Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA3.0 h
21.0 hours of engineering $3,680
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Scan for this in your stack

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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-2021-1624 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