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Big Ip Carrier Grade NatApplication · F5

CVE-2020-27720

HIGH · 7.5 CVSS v3.1 Published 2020-12-24
Fix available
A fix is available. Upgrade to 14.1.3.1 / 15.1.1 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges 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
On BIG-IP LTM/CGNAT version 16.0.0-16.0.0.1, 15.1.0-15.1.0.5, 14.1.0-14.1.3, and 13.1.0-13.1.3.5, when processing NAT66 traffic with Port Block Allocation (PBA) mode and SP-DAG enabled, and dag-ipv6-prefix-len configured with a value less than the default of 128, an undisclosed traffic pattern may cause the Traffic Management Microkernel (TMM) to restart.

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

A denial of service vulnerability in F5 BIG-IP LTM/CGNAT allows an attacker to cause TMM restart via specially crafted NAT66 traffic when Port Block Allocation (PBA) mode is enabled with SP-DAG and dag-ipv6-prefix-len configured to a value less than 128. The attack requires specific configuration conditions and an undisclosed traffic pattern.

MitigationUpgrade to a patched BIG-IP version or disable NAT66 PBA mode with SP-DAG if not required, and ensure dag-ipv6-prefix-len is set to the default value of 128 when these features are in use.

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
Big Ip Carrier Grade NatApplication
Affected:>= 13.1.0, <= 13.1.3>= 14.1.0, < 14.1.3.1>= 15.1.0, < 15.1.1>= 16.0.0, < 16.0.1
Big Ip Local Traffic ManagerApplication
Affected:>= 13.1.0, <= 13.1.3>= 14.1.0, < 14.1.3.1>= 15.1.0, < 15.1.1>= 16.0.0, < 16.0.1

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
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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify BIG-IP version
    Run the command to display system version information, such as `tmsh show /sys version` or check the web UI under System > Software Management > ISO Image
    Affected if The installed version falls within the affected ranges: 13.1.0-13.1.3, 14.1.0-14.1.3.0, 15.1.0-15.1.0, or 16.0.0-16.0.0
  2. Verify NAT66 configuration is in use
    Check the BIG-IP CGNAT or LTM NAT66 configuration settings via tmsh (e.g., `tmsh list /ltm nat` or `tmsh show /ltm nat`) or through the web UI configuration pages
    Affected if NAT66 (IPv6 NAT) is configured and active on the device
  3. Confirm Port Block Allocation mode is enabled
    Examine the CGNAT or NAT66 settings for PBA configuration, typically found in the NAT profile or CGNAT profile settings via tmsh or the web UI
    Affected if Port Block Allocation (PBA) mode is enabled for NAT66
  4. Check if SP-DAG is enabled
    Inspect the CGNAT or NAT configuration for Stateful Prefix Distributed Address Gateway (SP-DAG) settings via tmsh or the web UI
    Affected if SP-DAG feature is enabled in the NAT66 configuration
  5. Inspect dag-ipv6-prefix-len setting
    Review the DAG IPv6 prefix length configuration in the NAT or CGNAT profile settings via tmsh (e.g., `tmsh list /ltm nat` with relevant profile) or through the web UI
    Affected if dag-ipv6-prefix-len is set to a value less than 128 (the default is 128)

The environment is affected if the BIG-IP version is within the vulnerable range AND NAT66 with PBA mode AND SP-DAG are enabled AND dag-ipv6-prefix-len is set to less than 128.

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 14.1.3.1 / 15.1.1 / 16.0.1 or later
Fixed in 14.1.3.115.1.116.0.1
Interim mitigation

Upgrade to a patched BIG-IP version or disable NAT66 PBA mode with SP-DAG if not required, and ensure dag-ipv6-prefix-len is set to the default value of 128 when these features are in use.

Fix this in Big Ip Carrier Grade Nat 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
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,176.

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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-2020-27720 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