CVE-2021-23000Network attack vector

TMM restart via malformed HTTP request sequence

Published Mar 31, 2021 · Updated Aug 3, 2024

Denial of service in F5 Networks BIG-IP 13.1.3.4 through 13.1.3.5 and 12.1.5.2 allows remote attackers to restart TMM via HTTP requests. The TMM HTTP parser mishandles an undisclosed request sequence when RFC enforcement is enabled or an AFM profile checks Bad host headers. Exploitation requires one of those non-default conditions, and the resulting restart temporarily interrupts traffic processing.

CVSS severity7.5
High
EPSS probability0.93%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in F5 Networks BIG-IP 13.1.3.4 through 13.1.3.5 and 12.1.5.2 allows remote attackers to restart TMM via HTTP requests. The TMM HTTP parser mishandles an undisclosed request sequence when RFC enforcement is enabled or an AFM profile checks Bad host headers. Exploitation requires one of those non-default conditions, and the resulting restart temporarily interrupts traffic processing.

The record

CVE
CVE-2021-23000
Published
Mar 31, 2021
Updated
Aug 3, 2024
Vendor
F5 Networks
Product
BIG-IP
Classifications
T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 31, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=13.1.3.4-13.1.3.5, 12.1.5.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

F5 Networks · BIG-IPversion=13.1.3.4-13.1.3.5, 12.1.5.2

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:P
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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