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Ios XeOperating system · Cisco

CVE-2020-3509

HIGH · 8.6 CVSS v3.1 Published 2020-09-24
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 DHCP message handler of Cisco IOS XE Software for Cisco cBR-8 Converged Broadband Routers could allow an unauthenticated, remote attacker to cause the supervisor to crash, which could result in a denial of service (DoS) condition. The vulnerability is due to insufficient error handling when DHCP version 4 (DHCPv4) messages are parsed. An attacker could exploit this vulnerability by sending a malicious DHCPv4 message to or through a WAN interface of an affected device. A successful exploit could allow the attacker to cause a reload of the affected device. Note: On Cisco cBR-8 Converged Broadband Routers, all of the following are considered WAN interfaces: 10 Gbps Ethernet interfaces 100 Gbps Ethernet interfaces Port channel interfaces that include multiple 10 and/or 100 Gbps Ethernet interfaces

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

The vulnerability exists in the DHCPv4 message handler of Cisco IOS XE Software on cBR-8 Converged Broadband Routers. An unauthenticated remote attacker can send malformed DHCPv4 packets through WAN interfaces (10G/100G Ethernet or port channels), exploiting insufficient error handling in the DHCP parser that causes the supervisor to crash and force a device reload.

MitigationApply the Cisco IOS XE software update addressing CVE-2020-3509 when released; as a temporary mitigation, filter or rate-limit inbound DHCP traffic on WAN 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 XeOperating system
Affected:= 16.7\(1\)

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 model
    Run 'show version' or 'show platform' and look for 'cBR-8' or 'Converged Broadband Router' in the output
    Affected if The device is NOT a Cisco cBR-8 Converged Broadband Router (if different model, this CVE does not apply)
  2. Check the IOS XE version
    Run 'show version' and locate the software version string (typically displayed as 'Version 16.7(1)' or similar)
    Affected if The version is 16.7(1) exactly - this is the only version listed as affected in the provided advisory
  3. Verify DHCPv4 is enabled on WAN interfaces
    Run 'show ip dhcp import' and 'show running-config | include dhcp' to check DHCP configuration; examine WAN interface configs with 'show interfaces' for 10G/100G Ethernet or port-channel interfaces
    Affected if DHCPv4 processing is enabled on WAN interfaces (10G/100G Ethernet or port channels) - the vulnerability is triggered by malformed DHCPv4 packets arriving on these interfaces
  4. Confirm WAN interface status
    Run 'show ip interface brief' or 'show interfaces' to list active WAN interfaces (10G, 100G, or port-channel)
    Affected if WAN interfaces are up and processing traffic - the attack requires sending malformed DHCPv4 packets through these interfaces

You are affected only if you are running Cisco IOS XE version 16.7(1) on a cBR-8 Converged Broadband Router with DHCPv4-enabled WAN interfaces that can receive inbound DHCP traffic.

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 addressing CVE-2020-3509 when released; as a temporary mitigation, filter or rate-limit inbound DHCP traffic on WAN interfaces.

Fix this in Ios Xe Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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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-2020-3509 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