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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 3 May 2022.
Ios XrOperating system · Cisco

CVE-2020-3566

HIGH · 8.6 CVSS v3.1 Published 2020-08-29
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
In the wild 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 Distance Vector Multicast Routing Protocol (DVMRP) feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to exhaust process memory of an affected device. The vulnerability is due to insufficient queue management for Internet Group Management Protocol (IGMP) packets. An attacker could exploit this vulnerability by sending crafted IGMP traffic to an affected device. A successful exploit could allow the attacker to cause memory exhaustion, resulting in instability of other processes. These processes may include, but are not limited to, interior and exterior routing protocols. Cisco will release software updates 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

This vulnerability exists in Cisco IOS XR Software's Distance Vector Multicast Routing Protocol (DVMRP) feature. The root cause is insufficient queue management for Internet Group Management Protocol (IGMP) packets. An unauthenticated remote attacker can send specially crafted IGMP traffic to exhaust the process memory on the affected device, causing instability in critical processes including interior and exterior routing protocols.

MitigationApply the Cisco software update when available. In the interim, filter or rate-limit IGMP traffic from untrusted sources at network borders to reduce exposure to unauthenticated attackers.

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:= 6.4.2

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 device OS
    Run 'show version' or check the system banner to confirm the device runs Cisco IOS XR software
    Affected if The device is not running Cisco IOS XR, then this CVE does not apply
  2. Check the IOS XR version
    Execute 'show version' and locate the software version string (e.g., 6.4.2)
    Affected if The installed version matches exactly 6.4.2 (or falls within the affected range if broader ranges are published by Cisco)
  3. Verify DVMRP feature status
    Run 'show dvmrp interface' or 'show ip dvmrp interface' to check if DVMRP is enabled on any interfaces
    Affected if DVMRP is actively running on one or more interfaces - this is the vulnerable component
  4. Confirm IGMP configuration
    Execute 'show igmp interface' to see if IGMP is configured and running
    Affected if IGMP is enabled - the vulnerability stems from insufficient handling of IGMP packets within DVMRP
  5. Monitor for memory exhaustion
    Run 'show process memory' or 'show memory' to check for abnormally high memory usage in routing processes, particularly the DVMRP or IGMP-related processes
    Affected if Memory usage for DVMRP/IGMP processes is unusually high or continuously growing, indicating potential exploitation

A user is affected if the device runs Cisco IOS XR version 6.4.2, has DVMRP enabled, and is processing IGMP traffic that could trigger memory exhaustion in the DVMRP process.

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 the Cisco software update when available. In the interim, filter or rate-limit IGMP traffic from untrusted sources at network borders to reduce exposure to unauthenticated attackers.

Fix this in Ios Xr Exploited in the wild — priority engagement
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing6.0 h
  • Review / QA3.0 h
18.0 hours of engineering $3,120
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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-2020-3566 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