CVE-2021-23035Network attack vector

Service interruption via crafted chunked responses

Published Sep 14, 2021 · Updated Aug 3, 2024

Improper input validation in F5 Networks BIG-IP 14.1.x before 14.1.4.4 allows remote attackers to crash TMM via chunked responses. F5 has not disclosed which HTTP parser operation mishandles the packet sequence or how the chunked response reaches the fatal condition. Exposure requires an HTTP profile on a virtual server, and successful exploitation interrupts traffic handled by the terminated TMM process.

CVSS severity7.5
High
EPSS probability0.95%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in F5 Networks BIG-IP 14.1.x before 14.1.4.4 allows remote attackers to crash TMM via chunked responses. F5 has not disclosed which HTTP parser operation mishandles the packet sequence or how the chunked response reaches the fatal condition. Exposure requires an HTTP profile on a virtual server, and successful exploitation interrupts traffic handled by the terminated TMM process.

The record

CVE
CVE-2021-23035
Published
Sep 14, 2021
Updated
Aug 3, 2024
Vendor
F5 Networks
Product
BIG-IP
Classifications
CWE-20, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 14, 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=14.1.x before 14.1.4.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

F5 Networks · BIG-IPversion=14.1.x before 14.1.4.4

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.1NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:C

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

CWE-20Improper Input Validation
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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