Cloud FoundationApplication · VMware
CVE-2021-21994
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedSFCB (Small Footprint CIM Broker) as used in ESXi has an authentication bypass vulnerability. A malicious actor with network access to port 5989 on ESXi may exploit this issue to bypass SFCB authentication by sending a specially crafted request.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceSFCB (Small Footprint CIM Broker) in VMware ESXi contains an authentication bypass vulnerability. An unauthenticated attacker with network access to port 5989 can send specially crafted requests to bypass SFCB authentication and potentially execute code or access CIM services.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Cloud FoundationApplication
>= 3.0, < 3.10.2>= 4.0, < 4.3
EsxiOperating system
= 6.5= 6.7= 7.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed ESXi versionRun 'esxcli system version get' or check vSphere Client host summary to obtain the ESXi build versionAffected if The version is 6.5, 6.7, or 7.0 (any patch level within these major versions)
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Verify SFCB service is runningCheck if the SFCB (Small Footprint CIM Broker) service is active on the host using '/etc/init.d/sfcbd status' or via 'esxcli system services list'Affected if SFCB service is running and enabled
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Confirm port 5989 is listeningRun 'esxcli network ip connection list | grep 5989' or use 'netstat -an | grep 5989' to check if CIM/SFCB port is open and listeningAffected if Port 5989 shows as LISTEN and is bound to an accessible network interface
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Check firewall exposure of port 5989Review firewall rules using 'esxcli network firewall ruleset list' and 'esxcli network firewall ruleset rule list' to determine if port 5989 is accessible from external networksAffected if Firewall permits incoming connections to port 5989 from untrusted networks
A user is affected if their ESXi version is 6.5, 6.7, or 7.0 AND SFCB is running with port 5989 exposed to network attackers.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped3.10.24.3
Apply VMware security patches for CVE-2021-21994 to affected ESXi hosts; if patching is not immediately possible, restrict network access to port 5989 through firewall rules or disable SFCB if CIM functionality is not required.
ESXi 6.5 -> 6.5 P05 or later; ESXi 6.7 -> 6.7 P03 or later; ESXi 7.0 -> 7.0 P02 or later; Cloud Foundation -> 3.10.2 or 4.3
- 1. Identify all ESXi hosts and Cloud Foundation installations in your environment that are running affected versions (ESXi 6.5, 6.7, or 7.0; Cloud Foundation 3.x < 3.10.2 or 4.x < 4.3)
- 2. Review VMware Security Advisory VMSA-2021-0018 for the complete list of fixed versions and patch bundles
- 3. For ESXi 6.5: Upgrade to ESXi 6.5 P05 (ESXi650-202102001) or later
- 4. For ESXi 6.7: Upgrade to ESXi 6.7 P03 (ESXi670-202102001) or later
- 5. For ESXi 7.0: Upgrade to ESXi 7.0 P02 (ESXi700-202102001) or later
- 6. For Cloud Foundation: Upgrade to 3.10.2 or 4.3 respectively
- 7. Create a maintenance window and follow standard VMware upgrade procedures
- 8. After upgrade, verify SFCB service (port 5989) is running correctly and CIM clients can authenticate
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Cloud Foundation
Scoped from the published advisory
- Consultation3.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,800.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-21994 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-21994 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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