CVE-2021-27259
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 · uneditedThis vulnerability allows local attackers to escalate privileges on affected installations of Parallels Desktop 16.0.1-48919. 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 user-supplied data, which can result in an integer overflow before allocating a buffer. An attacker can leverage this vulnerability to escalate privileges and execute arbitrary code in the context of the hypervisor. Was ZDI-CAN-12021.
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 confidenceInteger overflow vulnerability in Parallels Desktop's Toolgate component allows a low-privileged attacker on a guest VM to escape into the hypervisor context by exploiting insufficient validation of user-supplied data during buffer allocation, leading to arbitrary code execution with hypervisor privileges.
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= 16.0.1CVSS 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
- High
- Privileges
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:H/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 checksWork through these to decide whether this CVE applies to you.
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Confirm Parallels Desktop is installedCheck for the presence of Parallels Desktop application on the host system. On macOS, look for /Applications/Parallels Desktop.app or check System Settings > Privacy & Security > Extensions for Parallels extensions.Affected if Parallels Desktop is not installed on the system.
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Identify installed Parallels Desktop versionOpen Parallels Desktop and navigate to Help > About Parallels Desktop, or run 'prlctl --version' command in Terminal if available, or check /Applications/Parallels Desktop.app/Contents/Info.plist for CFBundleVersion.Affected if The installed version is exactly 16.0.1.
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Verify Toolgate component statusCheck if Toolgate functionality is available by examining Parallels configuration files or running 'prlctl list -a' to list all VMs. Toolgate is a paravirtualization interface used for guest-to-host communication.Affected if Toolgate is enabled and VMs are running on the affected version 16.0.1.
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Determine if running as guest VMIdentify whether this system is a guest VM by checking for Parallels-specific artifacts: look for prl_* kernel extensions, check system profiler for virtual hardware indicators, or run 'ioreg -l | grep -i parallels'.Affected if This system is a guest VM running on Parallels Desktop version 16.0.1 with Toolgate active.
The environment is affected if Parallels Desktop version 16.0.1 is installed and running, with the Toolgate component enabled and active guest VMs present.
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.
From vendor dataApply Parallels Desktop security updates that address the Toolgate input validation flaw; ensure guest systems do not run untrusted code from unknown sources.
- Consultation2.0 h
- Implementation4.0 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 $3,328.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-27259 — 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-2021-27259 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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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.
- 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
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