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iOSOperating system · Cisco

CVE-2018-0123

MEDIUM · 5.5 CVSS v3.0 Published 2018-02-08
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
57/100
Remediation priority · Elevated
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 Path Traversal vulnerability in the diagnostic shell for Cisco IOS and IOS XE Software could allow an authenticated, local attacker to use certain diagnostic shell commands that can overwrite system files. These system files may be sensitive and should not be able to be overwritten by a user of the diagnostic shell. The vulnerability is due to lack of proper input validation for certain diagnostic shell commands. An attacker could exploit this vulnerability by authenticating to the device, entering the diagnostic shell, and providing crafted user input to commands at the local diagnostic shell CLI. Successful exploitation could allow the attacker to overwrite system files that should be restricted. Cisco Bug IDs: CSCvg41950.

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 path traversal vulnerability exists in the diagnostic shell for Cisco IOS and IOS XE Software. An authenticated, local attacker who gains access to the diagnostic shell can provide crafted input to certain CLI commands that bypass validation, allowing the attacker to overwrite sensitive system files that should be restricted from modification. The root cause is insufficient input validation on diagnostic shell commands.

MitigationApply the relevant Cisco software update/patch for Cisco IOS and IOS XE to address CSCvg41950. Until patched, restrict administrative access to devices and limit diagnostic shell usage to trusted personnel only following least-privilege principles.

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:= 16.7\(1\)
Ios XeOperating system
Affected:all versions

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
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.0/AV:L/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 or IOS XE version
    Use the 'show version' command from privileged EXEC mode to display the running software version
    Affected if The displayed version falls within or matches the affected version range (iOS 16.7(1) or any IOS XE version)
  2. Confirm diagnostic shell availability
    Attempt to access the diagnostic shell by typing 'diagnostic shell' or checking if the diagnostic mode is available via '?','
    Affected if The diagnostic shell is accessible and accepts commands without error messages indicating it is disabled
  3. Verify diagnostic shell is enabled in configuration
    Run 'show running-config | include diagnostic' or check the configuration for any diagnostic-related enable statements
    Affected if Diagnostic shell is enabled in the device configuration
  4. Check for existing diagnostic shell users
    Use 'show users' or review AAA authentication logs to identify users currently in diagnostic shell mode
    Affected if Any authenticated user has active access to diagnostic shell

The device is affected if it runs an affected iOS or IOS XE version and has diagnostic shell enabled and accessible to authenticated users.

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 relevant Cisco software update/patch for Cisco IOS and IOS XE to address CSCvg41950. Until patched, restrict administrative access to devices and limit diagnostic shell usage to trusted personnel only following least-privilege principles.

Fix this in iOS Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,130
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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-2018-0123 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