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Ios XeOperating system · Cisco

CVE-2025-20189

HIGH · 7.4 CVSS v3.1 Published 2025-05-07
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
79/100
Remediation priority · High
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 Cisco Express Forwarding functionality of Cisco IOS XE Software for Cisco ASR 903 Aggregation Services Routers with Route Switch Processor 3 (RSP3C) could allow an unauthenticated, adjacent attacker to trigger a denial of service (DoS) condition. This vulnerability is due to improper memory management when Cisco IOS XE Software is processing Address Resolution Protocol (ARP) messages. An attacker could exploit this vulnerability by sending crafted ARP messages at a high rate over a period of time to an affected device. A successful exploit could allow the attacker to exhaust system resources, which eventually triggers a reload of the active route switch processor (RSP). If a redundant RSP is not present, the router 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 · moderate confidence

A memory management flaw in the Cisco Express Forwarding (CEF) subsystem of Cisco IOS XE on ASR 903 routers with RSP3C processors allows an adjacent, unauthenticated attacker to trigger resource exhaustion by sending crafted ARP messages at high rates. This causes the active Route Switch Processor to reload, resulting in denial of service.

MitigationApply the Cisco-provided patch when available; in the interim, implement ARP rate limiting and ACLs on exposed interfaces to restrict adjacent attacker access.

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:= 3.16.0cs= 3.16.0s= 3.16.1as= 3.16.1s= 3.16.2as= 3.16.2bs= 3.16.2s= 3.16.3as= 3.16.3s= 3.16.4as= 3.16.4bs= 3.16.4ds

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
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:A/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 router hardware model
    Run 'show platform' or 'show version' and look for ASR 903 in the hardware description
    Affected if The router is not an ASR 903 series device, the vulnerability does not apply
  2. Confirm the RSP3C processor module
    Run 'show module' or 'show inventory' and verify the presence of RSP3 in the module listing
    Affected if The router does not have an RSP3 or RSP3C module installed, the vulnerability does not apply
  3. Check the installed IOS XE version
    Run 'show version' and locate the IOS XE software version in the output. Compare the full version string against the affected versions: 3.16.0cs, 3.16.0s, 3.16.1as, 3.16.1s, 3.16.2as, 3.16.2bs, 3.16.2s, 3.16.3as, 3.16.3s, 3.16.4as, 3.16.4bs, 3.16.4ds
    Affected if The installed version exactly matches one of the listed affected versions, the system is potentially vulnerable
  4. Verify Cisco Express Forwarding is enabled
    Run 'show cef interface' or 'show ip cef' to check CEF operational status
    Affected if CEF is enabled and running, the crafted ARP traffic can trigger the memory exhaustion condition

You are affected if your ASR 903 router with RSP3C runs one of the listed 3.16.x IOS XE versions and has CEF enabled, allowing adjacent attackers to send high-rate ARP traffic that causes processor reload.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the Cisco-provided patch when available; in the interim, implement ARP rate limiting and ACLs on exposed interfaces to restrict adjacent attacker access.

Recommended fix Moderate confidence

Upgrade to the Cisco IOS XE fixed release specified in the CVE-2025-20189 security advisory (obtain exact version from sec.cloudapps.cisco.com)

  1. 1. Identify the current Cisco IOS XE software version on the affected ASR 903 router with RSP3C using 'show version' command
  2. 2. Access the Cisco Security Advisory at sec.cloudapps.cisco.com for CVE-2025-20189 to obtain the specific fixed release version
  3. 3. Download the fixed IOS XE release from Cisco's software download center
  4. 4. Before upgrading, ensure you have a valid configuration backup using 'show running-config' and 'show startup-config'
  5. 5. If the router has a redundant RSP, verify redundancy status using 'show redundancy'
  6. 6. Upgrade the IOS XE software following Cisco's standard upgrade procedures for ASR 903 routers
  7. 7. After upgrade, verify the new version is installed using 'show version'
  8. 8. Confirm Cisco Express Forwarding is operational using 'show ip cef'
Caveat Refer to Cisco's release notes for the target fixed version to check for any configuration or feature changes between 3.16.x and the fixed release

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

Fix this in Ios Xe Scoped from the published advisory
  • Consultation6.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,600
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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-2025-20189 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