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Parallels DesktopApplication · Parallels

CVE-2021-31420

HIGH · 8.8 CVSS v3.1 Published 2021-04-29
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
90/100
Remediation priority · Urgent
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
This vulnerability allows local attackers to escalate privileges on affected installations of Parallels Desktop 16.1.0-48950. An attacker must first obtain the ability to execute low-privileged code on the target guest system in order to exploit this vulnerability. The specific flaw exists within the Toolgate component. The issue results from the lack of proper validation of the length of user-supplied data prior to copying it to a fixed-length stack-based buffer. An attacker can leverage this vulnerability to escalate privileges and execute arbitrary code in the context of the hypervisor. Was ZDI-CAN-12220.

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 stack-based buffer overflow in the Toolgate component of Parallels Desktop 16.1.0-48950 allows local attackers who can execute low-privileged code on the guest VM to overflow a stack buffer by failing to validate the length of user-supplied data before copying, leading to hypervisor-level code execution and privilege escalation.

MitigationApply the vendor security update for Parallels Desktop; restrict execution of untrusted code within guest VMs to reduce 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
Parallels DesktopApplication
Affected:= 16.1.0-48950

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
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

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

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

  1. Verify Parallels Desktop is installed
    On the macOS host, check for the presence of Parallels Desktop application in /Applications or via system_profiler SPApplicationsByType command
    Affected if Parallels Desktop is not installed on the system
  2. Determine installed Parallels Desktop version
    Open Parallels Desktop, go to Parallels Desktop menu > About Parallels Desktop, or run: defaults read /Applications/Parallels\ Desktop.app/Contents/Info.plist CFBundleVersion
    Affected if Version displayed does not match 16.1.0-48950 exactly
  3. Confirm guest VMs are in use
    Check if any guest virtual machines are configured in Parallels Desktop by examining ~/Library/Parallels/ or the Parallels Desktop VM list
    Affected if Guest VMs exist and the Toolgate component is active between guest and host
  4. Check for code execution capability in guest
    Verify whether untrusted or low-privileged code can execute within any guest VM by reviewing VM configurations and installed software within guests
    Affected if Low-privileged or untrusted code execution is possible inside any guest VM

You are affected only if Parallels Desktop version 16.1.0-48950 is installed and you run guest VMs where an attacker could execute code to trigger the Toolgate buffer overflow.

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.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the vendor security update for Parallels Desktop; restrict execution of untrusted code within guest VMs to reduce attack surface.

Recommended fix Moderate confidence

Latest Parallels Desktop 16.x or newer version with security fix (verify current fixed release at kb.parallels.com)

  1. Verify the currently installed Parallels Desktop version by going to Parallels Desktop menu > About Parallels Desktop
  2. Navigate to the official Parallels knowledge base at kb.parallels.com to check for security updates related to CVE-2021-31420
  3. Download and install the latest available version of Parallels Desktop that includes the security fix for this vulnerability
  4. After updating, verify the installation by checking the version number in About Parallels Desktop matches the fixed release
Caveat Newer versions may introduce compatibility changes with older guest operating systems or require macOS updates; review release notes before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Parallels Desktop Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA6.0 h
30.0 hours of engineering $5,120
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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-2021-31420 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