dbcve.org
Ios XeOperating system · Cisco

CVE-2023-20187

HIGH · 7.5 CVSS v3.1 Published 2023-09-27
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
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 Multicast Leaf Recycle Elimination (mLRE) feature of Cisco IOS XE Software for Cisco ASR 1000 Series Aggregation Services Routers could allow an unauthenticated, remote attacker to cause the affected device to reload, resulting in a denial of service (DoS) condition. This vulnerability is due to incorrect handling of certain IPv6 multicast packets when they are fanned out more than seven times on an affected device. An attacker could exploit this vulnerability by sending a specific IPv6 multicast or IPv6 multicast VPN (MVPNv6) packet through the affected device. A successful exploit could allow the attacker to cause a reload of 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 · moderate confidence

A vulnerability in the Multicast Leaf Recycle Elimination (mLRE) feature of Cisco IOS XE Software on ASR 1000 Series routers allows an unauthenticated remote attacker to cause device reload via specially crafted IPv6 multicast or IPv6 multicast VPN (MVPNv6) packets. The flaw is due to incorrect handling of IPv6 multicast packets fanned out more than seven times, resulting in a denial of service condition.

MitigationApply the Cisco IOS XE software update that addresses this vulnerability; in the interim, consider filtering or rate-limiting IPv6 multicast traffic at network edges to reduce exposure.

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:= 3.7.1s= 3.7.2s= 3.7.2ts= 3.7.3s= 3.7.4s= 3.7.5s= 3.7.6s= 3.7.7s= 3.8.0s= 3.8.1s= 3.8.2s= 3.9.0s

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
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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 device model
    Run 'show version' or 'show platform' to confirm the hardware is an ASR 1000 Series router
    Affected if Device is NOT an ASR 1000 Series router (other models are not affected by this CVE)
  2. Check IOS XE version
    Run 'show version' and locate the IOS XE software version string (typically shown as 'Version 17.X.Y' or similar)
    Affected if Version matches any of these: 3.7.1s, 3.7.2s, 3.7.2ts, 3.7.3s, 3.7.4s, 3.7.5s, 3.7.6s, 3.7.7s, 3.8.0s, 3.8.1s, 3.8.2s, or 3.9.0s
  3. Verify mLRE feature status
    Run 'show ip mroute verbose' or 'show ipv6 mroute verbose' and look for mLRE-related configuration; also check 'show running-config | include mLRE' or 'multicast leaf-recycle' under the relevant routing context
    Affected if The mLRE (Multicast Leaf Recycle Elimination) feature is enabled in the configuration
  4. Confirm IPv6 multicast is active
    Run 'show ipv6 mroute' and 'show ipv6 mfib active' to check for active IPv6 multicast streams or MVPNv6 tunnels
    Affected if IPv6 multicast routing or IPv6 multicast VPN (MVPNv6) is configured and active on the device

A user is affected if they are running a vulnerable IOS XE version (3.7.1s through 3.9.0s) on an ASR 1000 Series router WITH the mLRE feature enabled AND IPv6 multicast or MVPNv6 traffic is being processed.

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 IOS XE software update that addresses this vulnerability; in the interim, consider filtering or rate-limiting IPv6 multicast traffic at network edges to reduce exposure.

Fix this in Ios Xe Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing5.0 h
  • Review / QA3.0 h
17.0 hours of engineering $2,970
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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-2023-20187 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