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Big Ip Access Policy ManagerApplication · F5

CVE-2021-23000

HIGH · 7.5 CVSS v3.1 Published 2021-03-31
Fix available
A fix is available. Upgrade to 13.1.3.6 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 versions 13.1.3.4-13.1.3.6 and 12.1.5.2, if the tmm.http.rfc.enforcement BigDB key is enabled in a BIG-IP system, or the Bad host header value is checked in the AFM HTTP security profile associated with a virtual server, in rare instances, a specific sequence of malicious requests may cause TMM to restart. 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 · moderate confidence

A denial of service vulnerability in BIG-IP TMM where specific sequences of malicious HTTP requests with malformed host headers can cause TMM to restart when either the tmm.http.rfc.enforcement BigDB key is enabled or the Bad host header check is configured in an AFM HTTP security profile.

MitigationDisable the tmm.http.rfc.enforcement BigDB setting or remove the Bad host header check from AFM HTTP security profiles, or upgrade to a patched BIG-IP version if available.

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:>= 13.1.3.4, < 13.1.3.6= 12.1.5.2
Big Ip Advanced Firewall ManagerApplication
Affected:>= 13.1.3.4, < 13.1.3.6= 12.1.5.2
Big Ip Advanced Web Application FirewallApplication
Affected:>= 13.1.3.4, < 13.1.3.6= 12.1.5.2
Big Ip AnalyticsApplication
Affected:>= 13.1.3.4, < 13.1.3.6= 12.1.5.2
Big Ip Application Acceleration ManagerApplication
Affected:>= 13.1.3.4, < 13.1.3.6= 12.1.5.2
Big Ip Application Security ManagerApplication
Affected:>= 13.1.3.4, < 13.1.3.6= 12.1.5.2
Big Ip Ddos Hybrid DefenderApplication
Affected:>= 13.1.3.4, < 13.1.3.6= 12.1.5.2
Big Ip Domain Name SystemApplication
Affected:>= 13.1.3.4, < 13.1.3.6= 12.1.5.2

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 installed BIG-IP version
    Run command 'tmsh show sys version' and locate the version number in the output.
    Affected if Version equals 12.1.5.2 OR version is 13.1.3.4 or 13.1.3.5 (any version >=13.1.3.4 but <13.1.3.6)
  2. Verify tmm.http.rfc.enforcement BigDB setting
    Run command 'tmsh list /db tmm.http.rfc.enforcement' and check the value returned.
    Affected if The setting is enabled or set to any value other than disabled
  3. Identify AFM HTTP security profiles with Bad host header check
    Run 'tmsh list /security firewall http-profile' to list all AFM HTTP security profiles, then for each profile run 'tmsh list /security firewall http-profile <profile_name>' and look for 'bad-host-header-check' under the profile settings.
    Affected if Any AFM HTTP security profile has the Bad host header check configured

The system is affected if the installed version is 12.1.5.2 or falls within 13.1.3.4 through 13.1.3.5 AND either the tmm.http.rfc.enforcement BigDB key is enabled OR an AFM HTTP security profile has the Bad host header check configured.

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 or later
Fixed in 13.1.3.6
Interim mitigation

Disable the tmm.http.rfc.enforcement BigDB setting or remove the Bad host header check from AFM HTTP security profiles, or upgrade to a patched BIG-IP version if available.

Fix this in Big Ip Access Policy Manager Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.

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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-2021-23000 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