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Ios XeOperating system · Cisco

CVE-2021-1390

MEDIUM · 6.7 CVSS v3.1 Published 2021-03-24
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
69/100
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 vulnerability in one of the diagnostic test CLI commands of Cisco IOS XE Software could allow an authenticated, local attacker to execute arbitrary code on an affected device. To exploit this vulnerability, the attacker would need to have valid user credentials at privilege level 15. This vulnerability exists because the affected software permits modification of the run-time memory of an affected device under specific circumstances. An attacker could exploit this vulnerability by authenticating to the affected device and issuing a specific diagnostic test command at the CLI. A successful exploit could trigger a logic error in the code that was designed to restrict run-time memory modifications. The attacker could take advantage of this logic error to overwrite system memory locations and execute arbitrary code on the underlying Linux operating system (OS) of the affected 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

A logic error in the diagnostic test CLI command of Cisco IOS XE Software allows an authenticated attacker with privilege level 15 credentials to modify run-time memory and execute arbitrary code on the underlying Linux OS. The vulnerability stems from insufficient restrictions on memory modification during specific diagnostic operations.

MitigationApply the Cisco IOS XE software update that addresses CVE-2021-1390. If patches are unavailable, limit administrative access and monitor for suspicious diagnostic command usage.

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:= 16.8.1= 16.8.1a= 16.8.1b= 16.8.1c= 16.8.1d= 16.8.1e= 16.8.1s= 16.8.2= 16.8.3= 16.9.1= 16.9.1a= 16.9.1b

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

CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/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 IOS XE version
    Run 'show version' or 'show version | include Version' to display the installed Cisco IOS XE software version
    Affected if The displayed version matches any of: 16.8.1, 16.8.1a, 16.8.1b, 16.8.1c, 16.8.1d, 16.8.1e, 16.8.1s, 16.8.2, 16.8.3, 16.9.1, 16.9.1a, or 16.9.1b
  2. Confirm the device runs IOS XE
    Check the output of 'show version' for 'IOS XE' in the software identification string
    Affected if The device is confirmed to be running Cisco IOS XE and the version matches the affected list from step 1
  3. Verify diagnostic test CLI is accessible
    Attempt to access diagnostic mode via 'test diagnostics' or 'diagnostic start' command, or check if diagnostic commands are listed in 'show command-tree' for privilege level 15
    Affected if Diagnostic test CLI commands are available to privilege level 15 users on the device
  4. Review logs for diagnostic command usage
    Run 'show logging' or check syslog servers for entries containing 'test diagnostics', 'diagnostic start', or similar diagnostic CLI invocations
    Affected if Unusual or unauthorized diagnostic commands appear in system logs

The device is affected if it runs any of the listed IOS XE versions (16.8.1 through 16.9.1b) AND has diagnostic test CLI functionality accessible to privilege level 15 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 Cisco IOS XE software update that addresses CVE-2021-1390. If patches are unavailable, limit administrative access and monitor for suspicious diagnostic command usage.

Fix this in Ios Xe Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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Scan for this in your stack

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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-2021-1390 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