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Ios XrOperating system · Cisco

CVE-2021-34708

MEDIUM · 6.7 CVSS v3.1 Published 2021-09-09
Fix available
A fix is available. Upgrade to 7.3.2 / 7.4.1 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
Multiple vulnerabilities in image verification checks of Cisco Network Convergence System (NCS) 540 Series Routers, only when running Cisco IOS XR NCS540L software images, and Cisco IOS XR Software for Cisco 8000 Series Routers could allow an authenticated, local attacker to execute arbitrary code on the underlying operating system. For more information about these vulnerabilities, see the Details section of this advisory.

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 exists in the image verification checks of Cisco NCS 540 Series Routers running NCS540L software and Cisco IOS XR Software for Cisco 8000 Series Routers. An authenticated, local attacker can exploit multiple vulnerabilities in the image verification mechanism to execute arbitrary code on the underlying operating system, achieving privilege escalation from authenticated user to full system control.

MitigationApply the Cisco IOS XR software update that addresses these image verification vulnerabilities. Contact Cisco for the specific fixed software version applicable to the affected NCS540L and Cisco 8000 series router deployments.

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 XrOperating system
Affected:< 7.3.2>= 7.4.0, < 7.4.1

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 router model
    Execute 'show inventory' or 'show platform' to confirm the hardware is a Cisco NCS 540 Series Router (specifically NCS540L) or Cisco 8000 Series Router
    Affected if Router model is NOT NCS540L or Cisco 8000 series - vulnerability does not apply
  2. Check IOS XR software version
    Execute 'show version' to display the installed Cisco IOS XR software version
    Affected if Version is less than 7.3.2 OR version is 7.4.0 or higher but less than 7.4.1 - router is in an affected version range
  3. Verify image verification is relevant
    The vulnerability exists in the image verification mechanism. Check if the router uses Cisco IOS XR software by confirming the OS type in 'show version' output
    Affected if Router is running Cisco IOS XR on an affected model and version - the image verification vulnerability is present regardless of specific configuration

You are affected if your router is a Cisco NCS540L or Cisco 8000 Series running Cisco IOS XR version less than 7.3.2, or version 7.4.0 through 7.4.0.x (any 7.4.0 release before 7.4.1).

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 7.3.2 / 7.4.1 or later
Fixed in 7.3.27.4.1
Interim mitigation

Apply the Cisco IOS XR software update that addresses these image verification vulnerabilities. Contact Cisco for the specific fixed software version applicable to the affected NCS540L and Cisco 8000 series router deployments.

Recommended fix High confidence

Cisco IOS XR 7.3.2 or 7.4.1 or later

  1. 1. Identify the current IOS XR version using 'show version' command
  2. 2. Determine if the current version is < 7.3.2 or >= 7.4.0 and < 7.4.1
  3. 3. For versions < 7.3.2: Plan upgrade to IOS XR 7.3.2 or later
  4. 4. For versions >= 7.4.0 and < 7.4.1: Plan upgrade to IOS XR 7.4.1 or later
  5. 5. Download the appropriate fixed IOS XR software image from Cisco (tools.cisco.com)
  6. 6. Verify the software image integrity using Cisco's published checksums
  7. 7. Back up the current router configuration
  8. 8. Install the new IOS XR image following Cisco's standard upgrade procedures
Caveat Review Cisco IOS XR release notes for any compatibility or configuration changes between current and target versions

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

Fix this in Ios Xr Scoped from the published advisory
  • Consultation4.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,840
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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-2021-34708 in production — separate from our analysis above.

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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