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StarosOperating system · Cisco

CVE-2021-1540

HIGH · 7.2 CVSS v3.1 Published 2021-06-04
Fix available
A fix is available. Upgrade to 21.16.9 / 21.17.10 or later.
See remediation →
78/100
Remediation priority · High
Remotely reachable 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 the authorization process of Cisco ASR 5000 Series Software (StarOS) could allow an authenticated, remote attacker to bypass authorization and execute a subset of CLI commands on an affected device. 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 · moderate confidence

Multiple vulnerabilities in the authorization process of Cisco ASR 5000 Series Software (StarOS) allow an authenticated remote attacker to bypass authorization checks and execute a subset of CLI commands they should not have access to. This represents a privilege escalation issue within the CLI command authorization framework, where the authentication layer passes but authorization enforcement is flawed.

MitigationApply the Cisco security update/patch for StarOS when available. Until then, implement network segmentation to restrict management interface access to trusted administrators and audit user command execution logs for anomalous activity.

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
StarosOperating system
Affected:< 21.16.9>= 21.17.0, < 21.17.10>= 21.18.0, < 21.18.16>= 21.19.0, < 21.19.11>= 21.19.n, < 21.19.n7>= 21.20.0, < 21.20.8
Virtualized Packet CoreApplication
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
Network
Complexity
Low
Privileges
High
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/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 running software platform
    Execute 'show version' or 'show system information' from the CLI prompt to identify if the system is running Cisco StarOS or Virtualized Packet Core (VPC)
    Affected if The output shows 'StarOS' or 'Virtualized Packet Core' as the software platform - both are affected by this CVE
  2. Check the StarOS version number
    Locate the version number in the 'show version' output (typically displayed as '21.x.x' or similar)
    Affected if The installed version falls within any of these ranges: < 21.16.9, >= 21.17.0 and < 21.17.10, >= 21.18.0 and < 21.18.16, >= 21.19.0 and < 21.19.11, >= 21.19.n and < 21.19.n7, or >= 21.20.0 and < 21.20.8
  3. Confirm VPC deployment
    If not StarOS, verify the system is deployed as Virtualized Packet Core by checking the product name or VPC instantiation method
    Affected if The system is any version of Cisco Virtualized Packet Core - all versions are affected
  4. Verify CLI user accounts exist
    Execute 'show admin users' or 'show users' to list configured administrative accounts and their assigned privilege levels
    Affected if Multiple CLI user accounts with different privilege levels exist - the authorization bypass allows lower-privilege users to execute higher-privilege commands
  5. Audit command execution logs
    Review system logs, audit logs, or 'show logs' output for commands executed by users that may exceed their documented privilege level
    Affected if Logs show commands executed outside the expected authorization scope for certain user accounts - indicating exploitation of the authorization bypass

A system is affected if it runs Cisco StarOS in any of the listed version ranges OR any version of Virtualized Packet Core, and has CLI user accounts where the authorization bypass could allow privilege escalation.

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
Upgrade available Upgrade to 21.16.9 / 21.17.10 / 21.18.16 or later
Fixed in 21.16.921.17.1021.18.16
Interim mitigation

Apply the Cisco security update/patch for StarOS when available. Until then, implement network segmentation to restrict management interface access to trusted administrators and audit user command execution logs for anomalous activity.

Fix this in Staros Scoped from the published advisory
  • Consultation4.0 h
  • Implementation6.0 h
  • Testing8.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,800
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,080.

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-2021-1540 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