StarosOperating system · Cisco
CVE-2021-1353
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 · uneditedA vulnerability in the IPv4 protocol handling of Cisco StarOS could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to a memory leak that occurs during packet processing. An attacker could exploit this vulnerability by sending a series of crafted IPv4 packets through an affected device. A successful exploit could allow the attacker to exhaust the available memory and cause an unexpected restart of the npusim process, leading to a DoS condition on the affected 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 · moderate confidenceA memory leak vulnerability in Cisco StarOS IPv4 packet processing allows unauthenticated remote attackers to send crafted IPv4 packets that exhaust available memory, causing the npusim process to unexpectedly restart and result in denial of service.
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
< 21.22.0
Virtualized Packet Core Single InstanceApplication
all versionsCVSS 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
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/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 checksWork through these to decide whether this CVE applies to you.
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Identify the productDetermine if the system is running Cisco StarOS or Cisco Virtualized Packet Core Single Instance (VPC-SI). Use 'show product' or 'show version' command to identify the platform.Affected if The product is Cisco StarOS with version < 21.22.0, or Cisco Virtualized Packet Core Single Instance (any version)
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Check the StarOS versionExecute 'show version' or 'show build' command to retrieve the installed StarOS version number.Affected if The installed version is earlier than 21.22.0 (e.g., 21.21.x, 21.20.x, earlier releases)
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Verify IPv4 packet processing is activeCheck if IPv4 packet processing is enabled on the device. Use 'show ip interface' or 'show ip configuration' to confirm IPv4 interfaces are configured and active.Affected if IPv4 interfaces are configured and processing IPv4 traffic
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Assess network exposure to untrusted IPv4 trafficReview network configuration to determine if the device is directly accessible from untrusted networks. Check ACLs, firewall rules, and interface exposure using 'show configuration' or 'show ip access-lists'.Affected if The device accepts IPv4 traffic from untrusted or external networks without adequate filtering
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Check for npusim process instabilityReview system logs and use 'show process npusim' to look for unexpected restarts, high memory usage, or crash history related to the npusim process.Affected if The npusim process has restarted unexpectedly or shows abnormal memory consumption
A system is affected if it runs Cisco StarOS version < 21.22.0 or any version of VPC-SI, has IPv4 packet processing enabled, and is exposed to untrusted IPv4 network traffic.
Generated from the published advisory. Verify against your own configuration.
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 data21.22.0
Apply the Cisco patch for CVE-2021-1353 to affected StarOS devices; until patched, implement network segmentation and ingress filtering to reduce exposure to untrusted IPv4 traffic.
Fix this in Staros
Scoped from the published advisory
- Consultation3.0 h
- Implementation4.0 h
- Testing2.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,168.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-1353 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-1353 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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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.
- 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
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