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Cloud FoundationApplication · VMware

CVE-2021-21995

HIGH · 7.5 CVSS v3.1 Published 2021-07-13
Fix available
A fix is available. Upgrade to 3.10.2 / 4.3 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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 · unedited
OpenSLP as used in ESXi has a denial-of-service vulnerability due a heap out-of-bounds read issue. A malicious actor with network access to port 427 on ESXi may be able to trigger a heap out-of-bounds read in OpenSLP service resulting in a denial-of-service condition.

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 confidence

A heap out-of-bounds read vulnerability exists in OpenSLP service on ESXi. An attacker with network access to port 427 can send specially crafted SLP packets to trigger the out-of-bounds read, causing the service to crash and resulting in denial of service. The vulnerability stems from insufficient bounds checking in OpenSLP's message parsing logic.

MitigationApply the VMware security patch for CVE-2021-21995 to affected ESXi hosts. If patching is not immediately feasible, block or filter external access to port 427 (TCP/UDP) at the network perimeter to limit attack surface.

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
Affected:>= 3.0, < 3.10.2>= 4.0, < 4.3
EsxiOperating system
Affected:= 6.5= 6.7= 7.0

CVSS 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
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify ESXi version
    Run 'esxcli system version get' on the ESXi host or check via vCenter inventory
    Affected if Version is 6.5, 6.7, or 7.0
  2. Verify OpenSLP service status
    Run 'esxcli system slp stats get' or check via 'chkconfig --list' on the ESXi host to see if slpd service is running
    Affected if OpenSLP service (slpd) is enabled or running
  3. Check port 427 network exposure
    Run a port scan against the ESXi host for port 427 (TCP and UDP) or inspect firewall rules using 'esxcli network firewall ruleset rule list'
    Affected if Port 427 is open and accessible from untrusted network segments

The environment is affected if running ESXi 6.5, 6.7, or 7.0 with OpenSLP service enabled and port 427 exposed to network attackers

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

From vendor data
Upgrade available Upgrade to 3.10.2 / 4.3 or later
Fixed in 3.10.24.3
Interim mitigation

Apply the VMware security patch for CVE-2021-21995 to affected ESXi hosts. If patching is not immediately feasible, block or filter external access to port 427 (TCP/UDP) at the network perimeter to limit attack surface.

Fix this in Cloud Foundation Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,780
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,848.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-21995 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data