CVE-2021-23042Network attack vector

Denial of service via undisclosed HTTP requests

Published Sep 14, 2021 · Updated Aug 3, 2024

Resource exhaustion in F5 BIG-IP allows remote attackers to interrupt service via undisclosed HTTP requests to a virtual server. F5 has not disclosed how the requests are processed, only that an HTTP profile causes a significant increase in system resource utilization. The virtual server must use an HTTP profile; affected branches are 12.1.x before 12.1.6, 13.1.x before 13.1.4, 14.1.x before 14.1.4, 15.1.x before 15.1.3, and 16.0.x before 16.0.1.2.

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

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Resource exhaustion in F5 BIG-IP allows remote attackers to interrupt service via undisclosed HTTP requests to a virtual server. F5 has not disclosed how the requests are processed, only that an HTTP profile causes a significant increase in system resource utilization. The virtual server must use an HTTP profile; affected branches are 12.1.x before 12.1.6, 13.1.x before 13.1.4, 14.1.x before 14.1.4, 15.1.x before 15.1.3, and 16.0.x before 16.0.1.2.

The record

CVE
CVE-2021-23042
Published
Sep 14, 2021
Updated
Aug 3, 2024
Vendor
F5 Networks
Product
BIG-IP
Classifications
CWE-400, T1499
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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=16.0.x before 16.0.1.2, 15.1.x before 15.1.3, 14.1.x before 14.1.4, 13.1.x before 13.1.4, and 12.1.x before 12.1.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

F5 Networks · BIG-IPversion=16.0.x before 16.0.1.2, 15.1.x before 15.1.3, 14.1.x before 14.1.4, 13.1.x before 13.1.4, and 12.1.x before 12.1.6

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

CWE-400Uncontrolled Resource Consumption
T1499Endpoint Denial of Service

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo