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iOSOperating system · Cisco

CVE-2018-0484

MEDIUM · 6.5 CVSS v3.0 Published 2019-01-10
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable 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 access control logic of the Secure Shell (SSH) server of Cisco IOS and IOS XE Software may allow connections sourced from a virtual routing and forwarding (VRF) instance despite the absence of the vrf-also keyword in the access-class configuration. The vulnerability is due to a missing check in the SSH server. An attacker could use this vulnerability to open an SSH connection to an affected Cisco IOS or IOS XE device with a source address belonging to a VRF instance. Once connected, the attacker would still need to provide valid credentials to access the device.

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

Cisco IOS and IOS XE SSH servers have a logic flaw where access-class ACLs meant to restrict SSH access by source IP are bypassed for connections originating from VRF (Virtual Routing and Forwarding) instances. When the access-class configuration lacks the 'vrf-also' keyword, the SSH server incorrectly allows connections sourced from VRF IP addresses despite the ACL not permitting them. Valid credentials are still required for authentication after the connection is established.

MitigationConfigure access-class statements with the 'vrf-also' keyword for any VRF instances that should be subject to SSH access restrictions, or ensure SSH access lists explicitly deny VRF-sourced connections if VRF access is not intended.

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
iOSOperating system
Affected:= 16.6.2= 16.6.4

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
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

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 Cisco IOS version
    Run 'show version' and locate the firmware version number in the output
    Affected if The version displayed is exactly 16.6.2 or 16.6.4
  2. Verify SSH server is enabled
    Run 'show ip ssh' or check configuration with 'show run | include ip ssh'
    Affected if SSH server is active and accepting connections
  3. Confirm VRF instances are configured
    Run 'show vrf' to list all VRF definitions present on the device
    Affected if One or more VRFs are defined and active
  4. Inspect SSH access-class configuration
    Run 'show run | include access-class' or examine the running config for 'ip ssh' commands with access-class ACLs. Look for whether 'vrf-also' keyword appears
    Affected if Access-class ACLs are applied to SSH but the 'vrf-also' keyword is NOT present in the configuration
  5. Check for VRF-based SSH connections
    Run 'show ssh' and correlate source IP addresses against VRF interface subnets using 'show vrf ip interface'
    Affected if Active SSH sessions originate from IP addresses within VRF address spaces

You are affected if you run Cisco IOS 16.6.2 or 16.6.4, have VRF instances configured, use access-class ACLs to restrict SSH without the vrf-also keyword, and have or accept SSH connections sourced from VRF interfaces.

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

Configure access-class statements with the 'vrf-also' keyword for any VRF instances that should be subject to SSH access restrictions, or ensure SSH access lists explicitly deny VRF-sourced connections if VRF access is not intended.

Fix this in iOS Scoped from the published advisory
  • Consultation3.0 h
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,800
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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-2018-0484 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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