CVE-2021-23018Network attack vector

Sensitive-data interception via cleartext cluster traffic

Published Jun 1, 2021 · Updated Aug 3, 2024

Cleartext transmission in F5 Networks NGINX Controller 3.x before 3.4.0 allows attackers to intercept intra-cluster traffic. Services in the Controller namespace exchange traffic over cleartext protocols instead of TLS. Exploitation requires visibility into traffic within the cluster, and exposure is limited to data transmitted by affected services.

CVSS severity7.4
High
EPSS probability0.54%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cleartext transmission in F5 Networks NGINX Controller 3.x before 3.4.0 allows attackers to intercept intra-cluster traffic. Services in the Controller namespace exchange traffic over cleartext protocols instead of TLS. Exploitation requires visibility into traffic within the cluster, and exposure is limited to data transmitted by affected services.

The record

CVE
CVE-2021-23018
Published
Jun 1, 2021
Updated
Aug 3, 2024
Vendor
F5 Networks
Product
NGINX Controller
Classifications
CWE-319, T1040
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 1, 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="3.x before 3.4.0"

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

F5 Networks · NGINX Controllerversion="3.x before 3.4.0"

Published CVSS scores

5.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:N
7.4NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

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-319Cleartext Transmission of Sensitive Information
T1040Network Sniffing

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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