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Big Ip Access Policy ManagerApplication · F5

CVE-2026-42920

HIGH · 7.5 CVSS v3.1 Published 2026-05-13
Fix available
A fix is available. Upgrade to after 17.5.1 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
When a Client SSL profile is configured with Allow Dynamic Record Sizing on a UDP virtual server, undisclosed traffic can cause the Traffic Management Microkernel (TMM) to terminate.  Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

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 confidence

This is a F5 BIG-IP vulnerability where a Client SSL profile configured with 'Allow Dynamic Record Sizing' on a UDP virtual server can be exploited by undisclosed traffic to crash the Traffic Management Microkernel (TMM), causing denial of service.

MitigationDisable 'Allow Dynamic Record Sizing' on Client SSL profiles attached to UDP virtual servers, or upgrade to a patched version if available. Identify affected virtual servers through configuration review.

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 Access Policy ManagerApplication
Affected:= 21.0.0>= 17.1.0, <= 17.1.3>= 17.5.0, <= 17.5.1>= 16.1.0, <= 16.1.6
Big Ip Advanced Firewall ManagerApplication
Affected:= 21.0.0>= 17.1.0, <= 17.1.3>= 17.5.0, <= 17.5.1>= 16.1.0, <= 16.1.6
Big Ip Advanced Web Application FirewallApplication
Affected:= 21.0.0>= 17.1.0, <= 17.1.3>= 17.5.0, <= 17.5.1>= 16.1.0, <= 16.1.6
Big Ip AnalyticsApplication
Affected:= 21.0.0>= 17.1.0, <= 17.1.3>= 17.5.0, <= 17.5.1>= 16.1.0, <= 16.1.6
Big Ip Application Acceleration ManagerApplication
Affected:= 21.0.0>= 17.1.0, <= 17.1.3>= 17.5.0, <= 17.5.1>= 16.1.0, <= 16.1.6
Big Ip Application Security ManagerApplication
Affected:= 21.0.0>= 17.1.0, <= 17.1.3>= 17.5.0, <= 17.5.1>= 16.1.0, <= 16.1.6
Big Ip Application Visibility And ReportingApplication
Affected:= 21.0.0>= 17.1.0, <= 17.1.3>= 17.5.0, <= 17.5.1>= 16.1.0, <= 16.1.6
Big Ip Automation ToolchainApplication
Affected:= 21.0.0>= 17.1.0, <= 17.1.3>= 17.5.0, <= 17.5.1>= 16.1.0, <= 16.1.6

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. Check the installed BIG-IP version
    Run `tmsh show /sys version` or `show sys version` at the TMSH prompt. Note the displayed version number.
    Affected if The version matches = 21.0.0; >= 17.1.0 and <= 17.1.3; >= 17.5.0 and <= 17.5.1; or >= 16.1.0 and <= 16.1.6.
  2. Identify Client SSL profiles with Allow Dynamic Record Sizing enabled
    Run `tmsh list /ltm profile client-ssl all-properties` and search for profiles where 'allow-dynamic-record-sizing' is set to 'enabled' or 'yes'.
    Affected if Any Client SSL profile has 'Allow Dynamic Record Sizing' explicitly enabled.
  3. Identify UDP virtual servers
    Run `tmsh list /ltm virtual all-properties` and identify virtual servers where the 'ip-protocol' property is set to 'udp'.
    Affected if There are virtual servers configured to use UDP protocol.
  4. Check which Client SSL profiles are attached to UDP virtual servers
    For each UDP virtual server identified, examine the 'profiles' section to see if a Client SSL profile is attached. Cross-reference with the profiles found in step 2.
    Affected if A Client SSL profile with 'Allow Dynamic Record Sizing' enabled is attached to a UDP virtual server.

You are affected if your BIG-IP version is in the vulnerable range AND you have a Client SSL profile with 'Allow Dynamic Record Sizing' enabled attached to a UDP virtual server.

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 a release after 17.5.1
Interim mitigation

Disable 'Allow Dynamic Record Sizing' on Client SSL profiles attached to UDP virtual servers, or upgrade to a patched version if available. Identify affected virtual servers through configuration review.

Recommended fix Moderate confidence

Upgrade to the next available maintenance release after your current version (16.1.7+, 17.1.4+, 17.5.2+, or 21.0.1+)

  1. 1. Identify the current BIG-IP version by running 'tmsh show sys version' on the command line
  2. 2. Download the appropriate patched version from the F5 Downloads portal (downloads.f5.com) based on your current major version (16.1.x, 17.1.x, 17.5.x, or 21.0.x)
  3. 3. Review the release notes for the target version to confirm the security fix for CVE-2026-42920 is included
  4. 4. Upload the ISO image to the BIG-IP device via the web interface (System > Software Management > Image List) or tmsh
  5. 5. Create a volume and install the new version: 'tmsh install sys software volume <volume-name> image <image-name>'
  6. 6. Reboot the BIG-IP device into the new volume to apply the fix
  7. 7. After upgrade, verify the Client SSL profile 'Allow Dynamic Record Sizing' setting on UDP virtual servers; if not needed, consider disabling it as a configuration alternative
Caveat Review F5 release notes for any known issues or configuration changes required after upgrade; test in non-production environment first

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

Fix this in Big Ip Access Policy Manager Scoped from the published advisory
  • Consultation4.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,120
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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-2026-42920 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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