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Ios XeOperating system · Cisco

CVE-2021-34729

MEDIUM · 6.7 CVSS v3.1 Published 2021-09-23
Fix available
A fix is available. Upgrade to after 17.3.1a or later.
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 the CLI of Cisco IOS XE SD-WAN Software and Cisco IOS XE Software could allow an authenticated, local attacker to execute arbitrary commands with elevated privileges on an affected device. This vulnerability is due to insufficient validation of arguments passed to certain CLI commands. An attacker could exploit this vulnerability by including malicious input in the argument of an affected command. A successful exploit could allow the attacker to execute arbitrary commands with elevated privileges on the underlying operating system. An attacker would need valid user credentials to exploit this vulnerability.

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

Command injection vulnerability in Cisco IOS XE CLI where insufficient validation of arguments passed to certain CLI commands allows an authenticated local attacker to inject and execute arbitrary OS commands with elevated privileges by including malicious input in affected command arguments.

MitigationApply Cisco's official IOS XE software updates when available. Until patched, restrict CLI access to trusted, least-privilege users and monitor for unauthorized command execution.

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:<= 17.3.1a
Ios Xe Sd WanOperating system
Affected:<= 17.3.1a

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. Confirm the device runs Cisco IOS XE
    Execute 'show version' or 'show inventory' at the CLI and verify the software platform shows 'IOS XE' rather than classic IOS, NX-OS, or other platforms.
    Affected if The device is not running Cisco IOS XE (the vulnerability only affects IOS XE and IOS XE SD-WAN).
  2. Identify the installed IOS XE version
    Run 'show version' and locate the version string (typically in the format 17.x.x). Compare against the affected range: any version <= 17.3.1a.
    Affected if The displayed version number is 17.3.1a or earlier.
  3. Determine if the IOS XE SD-WAN feature is enabled
    Check the configuration or run 'show sdwan version' or 'show version | include SD-WAN' to see if the SD-WAN variant is installed. Also check 'show hardware' for SD-WAN-specific hardware modules.
    Affected if The device is running IOS XE SD-WAN variant in any affected version.
  4. Verify authenticated local CLI access exists
    Review user accounts with privilege level 15 (full administrative access) using 'show users' or 'show privilege'. Check local username configurations via 'show running-config | include username'.
    Affected if Untrusted or unauthorized accounts with CLI access exist on the device, allowing local authenticated attack.
  5. Audit recent CLI command history for anomalies
    Use 'show history' or review system logging (syslog) for suspicious commands executed around the time of potential compromise. Look for unexpected command patterns or execution at unusual times.
    Affected if Unauthorized or suspicious CLI commands appear in logs or history, especially commands originating from affected argument inputs.

The device is affected if it runs Cisco IOS XE or IOS XE SD-WAN version 17.3.1a or earlier AND has authenticated local CLI accounts that could inject malicious arguments into vulnerable command parameters.

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.

dbcve · scoped
Upgrade available Upgrade to a release after 17.3.1a
Interim mitigation

Apply Cisco's official IOS XE software updates when available. Until patched, restrict CLI access to trusted, least-privilege users and monitor for unauthorized command execution.

Recommended fix Moderate confidence

Cisco IOS XE 17.3.2 or later (any release > 17.3.1a)

  1. 1. Identify the current IOS XE version on the device using the 'show version' command
  2. 2. If the version is 17.3.1a or earlier, plan for an upgrade
  3. 3. Download the fixed IOS XE release from Cisco (version higher than 17.3.1a)
  4. 4. Review Cisco IOS XE software upgrade instructions for your specific hardware platform
  5. 5. Back up the current device configuration
  6. 6. Upload the new IOS XE image to the device
  7. 7. Set the boot variable to point to the new image
  8. 8. Reload the device to apply the new image
Caveat Review Cisco release notes for any relevant changes to features or compatibility in the target release

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Ios Xe Scoped from the published advisory
  • Consultation4.0 h
  • Implementation12.0 h
  • Testing8.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,880
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $7,808.

Scan for this in your stack

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dbcve dependency scanner

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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-2021-34729 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