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Ios XeOperating system · Cisco

CVE-2021-1453

MEDIUM · 6.8 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 →
73/100
Remediation priority · Elevated
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 software image verification functionality of Cisco IOS XE Software for the Cisco Catalyst 9000 Family of switches could allow an unauthenticated, physical attacker to execute unsigned code at system boot time. The vulnerability is due to an improper check in the code function that manages the verification of the digital signatures of system image files during the initial boot process. An attacker could exploit this vulnerability by loading unsigned software on an affected device. A successful exploit could allow the attacker to boot a malicious software image or execute unsigned code and bypass the image verification check part of the secure boot process of an affected device. To exploit this vulnerability, the attacker would need to have unauthenticated physical access to the device or obtain privileged access to the root shell on 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

This vulnerability in Cisco IOS XE for Catalyst 9000 switches allows an attacker to bypass the image verification check during the boot process by exploiting an improper check in the digital signature verification function. Successful exploitation enables booting unsigned software or executing arbitrary unsigned code at system startup, effectively bypassing secure boot protections.

MitigationApply the Cisco patch/firmware update for CVE-2021-1453 to all affected Catalyst 9000 series switches. Since exploitation requires physical access or root shell privileges, ensure physical security controls and restrict root access as compensating measures until patching is complete.

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:= 3.15.1xbs= 3.15.2xbs= 16.6.1= 16.6.2= 16.6.3= 16.6.4= 16.6.4a= 16.6.4s= 16.6.5= 16.6.6= 16.6.7= 16.6.8

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

CVSS:3.1/AV:P/AC:L/PR:N/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 device model and software platform
    Run 'show version' or 'show inventory' to confirm the device is a Cisco Catalyst 9000 series switch running Cisco IOS XE software.
    Affected if The device is a Catalyst 9000 series switch running IOS XE.
  2. Determine the IOS XE version
    Run 'show version' and locate the 'IOS XE' or 'Software' version line. Compare this version number exactly against the affected versions: 3.15.1xbs, 3.15.2xbs, 16.6.1, 16.6.2, 16.6.3, 16.6.4, 16.6.4a, 16.6.4s, 16.6.5, 16.6.6, 16.6.7, 16.6.8.
    Affected if The installed IOS XE version matches one of the listed affected versions.
  3. Check if secure boot is configured
    Run 'show secure-boot' to display the secure boot status. Also run 'show platform' or consult the boot configuration to verify whether secure boot is enabled on the system.
    Affected if Secure boot is enabled (the vulnerability allows bypassing it, so if secure boot is active, the device is a target for exploitation).
  4. Inspect boot logs and system startup messages
    During or after boot, examine console output or run 'show logging' to look for any anomalies in the boot process, such as signature verification failures, unexpected boot prompts, or indications that unsigned code was loaded.
    Affected if There are irregularities in boot process logs or evidence that unsigned software was loaded.

If the device is a Catalyst 9000 switch running IOS XE version 16.6.x or 3.15.xbs matching the affected list and secure boot is enabled, the environment is potentially affected by this vulnerability.

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 patch/firmware update for CVE-2021-1453 to all affected Catalyst 9000 series switches. Since exploitation requires physical access or root shell privileges, ensure physical security controls and restrict root access as compensating measures until patching is complete.

Fix this in Ios Xe Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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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-2021-1453 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