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StarosOperating system · Cisco

CVE-2021-1539

HIGH · 8.8 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 →
94/100
Remediation priority · Urgent
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

This vulnerability allows an authenticated remote attacker to bypass authorization checks in Cisco ASR 5000 Series StarOS software, enabling execution of CLI commands outside their granted privilege level. The attacker needs valid credentials but can leverage the flaw to run commands they are not authorized to execute.

MitigationApply the vendor patch from Cisco for this authorization bypass; until patched, strictly limit CLI access to trusted administrators only and monitor for anomalous 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
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
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/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 product and software version
    Log into the CLI and run 'show version' or check the system banner to confirm whether the device is running Cisco StarOS (ASR 5000 Series) or Virtualized Packet Core
    Affected if The device runs Cisco StarOS or Virtualized Packet Core and the version falls outside the fixed releases (21.16.9, 21.17.10, 21.18.16, 21.19.11, 21.20.8 or later)
  2. Compare StarOS version against affected ranges
    If running StarOS, note the full version number from 'show version' output and compare it against the affected 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, >= 21.20.0 and < 21.20.8
    Affected if The installed StarOS version matches any of these ranges, or for Virtualized Packet Core, any version is running
  3. Confirm CLI authentication is enabled
    Review the CLI access configuration by running 'show configuration' or checking the admin user account settings to verify that remote or local CLI authentication is active
    Affected if CLI access is enabled with valid user accounts, providing the attacker with the credentials needed to exploit the authorization bypass
  4. Audit CLI command logs for privilege escalation
    Review system logs, audit logs, or run 'show logs' to examine recent CLI command execution history, looking for commands executed by users operating outside their expected privilege level
    Affected if Logs show commands executed by users that should not be permitted based on their assigned privilege group or role

The environment is affected if the device runs Cisco StarOS in any version before 21.16.9, 21.17.10, 21.18.16, 21.19.11, or 21.20.8, or runs any version of Virtualized Packet Core, and CLI access with valid credentials is available.

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 21.16.9 / 21.17.10 / 21.18.16 or later
Fixed in 21.16.921.17.1021.18.16
Interim mitigation

Apply the vendor patch from Cisco for this authorization bypass; until patched, strictly limit CLI access to trusted administrators only and monitor for anomalous command execution.

Recommended fix Moderate confidence

StarOS 21.16.9, 21.17.10, 21.18.16, or 21.19.11 (or later) | Virtualized Packet Core: contact Cisco for specific fix

  1. 1. Identify the current StarOS version running on the affected Cisco ASR 5000 Series device
  2. 2. For StarOS: Upgrade to version 21.16.9 or later, 21.17.10 or later, 21.18.16 or later, or 21.19.11 or later
  3. 3. For Virtualized Packet Core: Contact Cisco for specific patch/upgrade guidance as no fixed version range was specified in the advisory
  4. 4. After upgrade, verify the authorization bypass is resolved by testing CLI command execution with limited-privilege accounts
  5. 5. Review user authorization roles and permissions to ensure proper access controls are in place
Caveat Review release notes for any CLI command changes or feature modifications between versions before upgrading

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

Fix this in Staros Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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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-2021-1539 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