CVE-2021-21994Network attack vector

Unauthenticated SFCB access via crafted network request

Published Jul 13, 2021 · Updated Aug 3, 2024

Authentication bypass in VMware ESXi 6.5 through 7.0 allows remote attackers to access SFCB through crafted requests to port 5989. VMware has not disclosed which SFCB authentication check mishandles the crafted request or what request element triggers the bypass. Network access to port 5989 and a running SFCB service, which is disabled by default, are required; the bounded impact is access past SFCB authentication.

CVSS severity9.8
Critical
EPSS probability1.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in VMware ESXi 6.5 through 7.0 allows remote attackers to access SFCB through crafted requests to port 5989. VMware has not disclosed which SFCB authentication check mishandles the crafted request or what request element triggers the bypass. Network access to port 5989 and a running SFCB service, which is disabled by default, are required; the bounded impact is access past SFCB authentication.

The record

CVE
CVE-2021-21994
Published
Jul 13, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-287, T1210
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 13, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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-287Improper Authentication
T1210Exploitation of Remote Services

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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