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Big Ip Advanced Web Application FirewallApplication · F5

CVE-2021-22976

HIGH · 7.5 CVSS v3.1 Published 2021-02-12
Fix available
A fix is available. Upgrade to 13.1.3.6 / 14.1.3.1 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 Advanced WAF and ASM version 16.0.x before 16.0.1.1, 15.1.x before 15.1.2, 14.1.x before 14.1.3.1, 13.1.x before 13.1.3.6, and all 12.1.x versions, when the BIG-IP ASM system processes WebSocket requests with JSON payloads, an unusually large number of parameters can cause excessive CPU usage in the BIG-IP ASM bd process. Note: Software versions which have reached End of Software Development (EoSD) 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 denial-of-service vulnerability in F5 BIG-IP ASM/Advanced WAF where specially crafted WebSocket requests containing JSON payloads with an unusually large number of parameters trigger excessive CPU consumption in the ASM bd process, potentially causing service disruption.

MitigationUpgrade BIG-IP ASM/Advanced WAF to version 16.0.1.1, 15.1.2, 14.1.3.1, or 13.1.3.6 or later. For 12.1.x versions (EoSD), consider upgrading to a supported version or implement rate limiting on WebSocket endpoints as a compensating control.

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 Advanced Web Application FirewallApplication
Affected:>= 12.1.0, <= 12.1.5>= 13.1.0, < 13.1.3.6>= 14.1.0, < 14.1.3.1>= 15.1.0, < 15.1.2>= 16.0.0, < 16.0.1.1
Big Ip Application Security ManagerApplication
Affected:>= 12.1.0, <= 12.1.5>= 13.1.0, < 13.1.3.6>= 14.1.0, < 14.1.3.1>= 15.1.0, < 15.1.2>= 16.0.0, < 16.0.1.1

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. Verify BIG-IP ASM or Advanced WAF module is provisioned
    Run 'tmsh list sys provision asm' or check the BIG-IP configuration for ASM provisioning status. The module must be provisioned for this vulnerability to apply.
    Affected if ASM or Advanced WAF module is not provisioned (then not affected)
  2. Determine the installed BIG-IP version
    Run 'tmsh show sys version' or check the BIG-IP System > Software Management page. Compare the version number against the affected ranges: 12.1.0-12.1.5, 13.1.0-13.1.3.5, 14.1.0-14.1.3.0, 15.1.0-15.1.1, 16.0.0-16.0.1.0
    Affected if Installed version falls within any of the affected version ranges listed
  3. Confirm WebSocket traffic is being processed by ASM
    Check ASM policy configuration for WebSocket traversal settings. Review the security policy applied to virtual servers handling WebSocket connections. WebSocket traffic must be allowed and inspected by ASM for the vulnerability to trigger.
    Affected if WebSocket traffic is not being inspected by ASM policies (then likely not affected)
  4. Monitor ASM bd process CPU usage
    Observe the 'bd' process CPU consumption using 'top' or 'bigtop -j' commands. Sustained high CPU usage in the bd process when WebSocket requests with JSON payloads are received may indicate exploitation.
    Affected if High bd process CPU usage is observed during WebSocket traffic with JSON payloads

The environment is affected if ASM or Advanced WAF is provisioned, the BIG-IP version is within the affected ranges, and WebSocket traffic with JSON payloads is being inspected by ASM policies.

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 13.1.3.6 / 14.1.3.1 / 15.1.2 or later
Fixed in 13.1.3.614.1.3.115.1.2
Interim mitigation

Upgrade BIG-IP ASM/Advanced WAF to version 16.0.1.1, 15.1.2, 14.1.3.1, or 13.1.3.6 or later. For 12.1.x versions (EoSD), consider upgrading to a supported version or implement rate limiting on WebSocket endpoints as a compensating control.

Fix this in Big Ip Advanced Web Application Firewall Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,560.

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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-2021-22976 in production — separate from our analysis above.

No notes yet

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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