dbcve.org
Ios XrOperating system · Cisco

CVE-2025-20146

HIGH · 8.6 CVSS v3.1 Published 2025-03-12
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 Layer 3 multicast feature of Cisco IOS XR Software for Cisco ASR 9000 Series Aggregation Services Routers, ASR 9902 Compact High-Performance Routers, and ASR 9903 Compact High-Performance Routers could allow an unauthenticated, remote attacker to cause a line card to reset, resulting in a denial of service (DoS) condition. This vulnerability is due to the incorrect handling of malformed IPv4 multicast packets that are received on line cards where the interface has either an IPv4 access control list (ACL) or a QoS policy applied. An attacker could exploit this vulnerability by sending crafted IPv4 multicast packets through an affected device. A successful exploit could allow the attacker to cause line card exceptions or a hard reset. Traffic over that line card would be lost while the line card reloads.

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 Layer 3 multicast feature allows unauthenticated remote attackers to cause line card resets by sending malformed IPv4 multicast packets through affected devices where interfaces have IPv4 ACLs or QoS policies applied. The root cause is incorrect handling of these crafted packets, leading to exceptions or hard resets.

MitigationApply Cisco IOS XR software updates when available; until then, consider filtering or rate-limiting unknown IPv4 multicast traffic at network edges and reviewing ACL/QoS configurations on affected interfaces.

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:= 7.9.21= 7.10.2= 7.11.1= 7.11.2= 7.11.21= 24.1.1= 24.1.2= 24.2.1= 24.2.2= 24.3.1= 24.3.2

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 Cisco IOS XR version
    Run 'show version' on the device CLI and locate the IOS XR release number in the output
    Affected if The version matches any of these: 7.9.21, 7.10.2, 7.11.1, 7.11.2, 7.11.21, 24.1.1, 24.1.2, 24.2.1, 24.2.2, 24.3.1, or 24.3.2
  2. Verify Layer 3 multicast feature is active
    Run 'show multicast routing' or 'show pim interface' to check if IPv4 multicast routing is enabled on any interface
    Affected if Multicast routing or PIM is actively running on the device
  3. Identify interfaces with IPv4 ACLs applied
    Run 'show ip access-lists interface' or review interface configurations with 'show running-config interface' to find ACL bindings
    Affected if Any interface has an IPv4 access control list applied inbound or outbound
  4. Identify interfaces with QoS policies applied
    Run 'show qos policy interface' or review interface configurations for service-policy statements
    Affected if Any interface has a QoS service policy attached
  5. Determine if multicast traffic can reach affected interfaces
    Check if interfaces with ACLs or QoS policies are also configured for multicast routing (PIM, IGMP), and verify multicast group membership exists with 'show igmp groups'
    Affected if Interfaces with ACLs or QoS policies also participate in multicast routing and can receive IPv4 multicast traffic

The device is likely affected if it runs one of the listed IOS XR versions AND has interfaces configured with both IPv4 multicast routing and ACL/QoS policies that can receive crafted IPv4 multicast packets.

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 Cisco IOS XR software updates when available; until then, consider filtering or rate-limiting unknown IPv4 multicast traffic at network edges and reviewing ACL/QoS configurations on affected interfaces.

Fix this in Ios Xr 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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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-2025-20146 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