Packet Data Network GatewayApplication · Cisco
CVE-2023-20051
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 Vector Packet Processor (VPP) of Cisco Packet Data Network Gateway (PGW) could allow an unauthenticated, remote attacker to stop ICMP traffic from being processed over an IPsec connection. This vulnerability is due to the VPP improperly handling a malformed packet. An attacker could exploit this vulnerability by sending a malformed Encapsulating Security Payload (ESP) packet over an IPsec connection. A successful exploit could allow the attacker to stop ICMP traffic over an IPsec connection and cause a denial of service (DoS).
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 confidenceThis vulnerability exists in Cisco PGW's Vector Packet Processor (VPP), where improper handling of malformed ESP packets over IPsec connections causes ICMP traffic processing to stop. An attacker can exploit this by sending specially crafted malformed ESP packets, resulting in denial of service for ICMP traffic.
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
Packet Data Network GatewayApplication
< 21.28.0CVSS 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
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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 Cisco PGW installationRun 'show version' or check system documentation to confirm the device is running Cisco Packet Data Network Gateway softwareAffected if The device is not a Cisco PGW, the vulnerability does not apply
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Check PGW software versionExecute 'show version' or access the admin interface to retrieve the installed Cisco PGW version numberAffected if The installed version is lower than 21.28.0 (for example, 21.27.0, 21.20.0, etc.)
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Verify VPP is enabledCheck the PGW configuration for Vector Packet Processor (VPP) status using 'show vpp summary' or reviewing the running configuration for VPP-related modulesAffected if VPP is actively enabled and processing packets; the flaw requires VPP to be running
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Confirm IPsec with ESP is in useReview IPsec tunnel configurations using 'show ipsec sa' or similar commands to verify Encapsulating Security Payload (ESP) tunnels are establishedAffected if IPsec connections using ESP protocol are active; the vulnerability is triggered by malformed ESP packets over these tunnels
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Monitor for ICMP traffic disruptionTest ICMP connectivity through the affected IPsec tunnels using ping or by reviewing traffic logs for ICMP processing failuresAffected if ICMP traffic is failing or stopping while other traffic types continue flowing through IPsec tunnels
A user is affected if they run Cisco PGW with a version below 21.28.0, have VPP enabled, and maintain active IPsec/ESP tunnels where ICMP traffic has stopped processing.
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.
dbcve · scoped21.28.0
Apply the Cisco vendor patch for CVE-2023-20051 once available. Until then, consider filtering malformed ESP packets at network boundaries or implementing alternative redundancy for affected IPsec tunnels.
Upgrade to Cisco Packet Data Network Gateway version 21.28.0 or later
- Identify the current version of Cisco Packet Data Network Gateway (PGW) running in the environment
- Verify the current version is below 21.28.0
- Plan an upgrade window and ensure configuration backups are in place
- Obtain the fixed release (21.28.0 or later) from Cisco's official software distribution
- Follow Cisco's standard upgrade procedure for PGW software
- After upgrade, verify the version is 21.28.0 or higher
- Test that ICMP traffic over IPsec connections is functioning properly
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Packet Data Network Gateway
Scoped from the published advisory
- Consultation4.0 h
- Implementation4.0 h
- Testing4.0 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 $3,968.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2023-20051 — 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-2023-20051 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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- 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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