dbcve.org
Big Ip Domain Name SystemApplication · F5

CVE-2020-27721

HIGH · 7.5 CVSS v3.1 Published 2020-12-24
Fix available
A fix is available. Upgrade to 14.1.3.1 / 15.1.2 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
In versions 16.0.0-16.0.0.1, 15.1.0-15.1.1, 14.1.0-14.1.3, 13.1.0-13.1.3.5, 12.1.0-12.1.5.2, and 11.6.1-11.6.5.2, in a BIG-IP DNS / BIG-IP LTM GSLB deployment, under certain circumstances, the BIG-IP DNS system may stop using a BIG-IP LTM virtual server for DNS response.

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

In BIG-IP DNS / LTM GSLB deployments, a vulnerability causes the BIG-IP DNS system to stop using a BIG-IP LTM virtual server for DNS responses under certain circumstances. This represents a denial-of-service condition where valid virtual servers are not utilized for DNS resolution.

MitigationUpgrade to a patched F5 BIG-IP version. Until then, monitor GSLB pool membership and DNS response paths to ensure virtual servers remain active.

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 Domain Name SystemApplication
Affected:>= 11.6.1, <= 11.6.5>= 12.1.0, <= 12.1.5>= 13.1.0, <= 13.1.3>= 14.1.0, < 14.1.3.1>= 15.0.0, < 15.1.2>= 16.0.0, < 16.0.1
Big Ip Global Traffic ManagerApplication
Affected:>= 11.6.1, <= 11.6.5>= 12.1.0, <= 12.1.5>= 13.1.0, <= 13.1.3>= 14.1.0, < 14.1.3.1>= 15.0.0, < 15.1.2>= 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 DNS or GTM deployment
    Log into the BIG-IP Configuration Utility or use tmsh command 'tmsh show sys module' to list enabled modules. Look for 'DNS' or 'GTM' (Global Traffic Manager) in the module list.
    Affected if The system does not have DNS or GTM modules enabled - the vulnerability only affects systems with these modules.
  2. Check installed BIG-IP version
    Run 'tmsh show sys version' or view the version in the BIG-IP Configuration Utility under Dashboard. Compare the version number to the affected ranges: 11.6.1-11.6.5, 12.1.0-12.1.5, 13.1.0-13.1.3, 14.1.0-14.1.3.0, 15.0.0-15.1.2, 16.0.0-16.0.0.
    Affected if The installed version falls within any of the affected version ranges.
  3. Verify GSLB pool configuration exists
    Use tmsh command 'tmsh show gtm pool' or access the GTM pools via Configuration Utility under DNS > GSLB > Pools. Confirm pools are defined and configured.
    Affected if No GSLB pools are configured - the vulnerability only impacts environments using GSLB pool members for DNS resolution.
  4. Inspect GSLB pool member status
    Run 'tmsh show gtm pool <pool_name> members' for each pool, or check via Configuration Utility under DNS > GSLB > Pools > Pool Members. Look for virtual server availability status.
    Affected if Pool members show as available but are not receiving DNS traffic, or virtual servers are missing from pool membership unexpectedly.
  5. Check DNS response paths for virtual server usage
    Use 'tmsh show gtm wideip' to view Wide IP statistics, then correlate with 'tmsh show ltm virtual' to see which virtual servers should be handling DNS resolution. Compare traffic statistics.
    Affected if Virtual servers configured as GSLB pool members are not being used for DNS responses despite showing as available in pool status.

A system is affected if it runs a vulnerable BIG-IP DNS or GTM version within the listed ranges AND uses GSLB pools where virtual servers are unexpectedly excluded from DNS resolution.

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 / 15.1.2 / 16.0.1 or later
Fixed in 14.1.3.115.1.216.0.1
Interim mitigation

Upgrade to a patched F5 BIG-IP version. Until then, monitor GSLB pool membership and DNS response paths to ensure virtual servers remain active.

Fix this in Big Ip Domain Name System Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,328.

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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-2020-27721 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