CVE-2021-34857

Guest-to-hypervisor code execution via Toolgate buffer overwrite

Published Oct 25, 2021 · Updated Aug 4, 2024

Out-of-bounds write in Toolgate in Parallels Desktop 16.1.3 (49160) allows guest OS users to execute arbitrary code in the hypervisor. Toolgate fails to validate guest-supplied data before writing it into an allocated buffer, permitting a write beyond the buffer boundary. Exploitation requires high-privileged code execution inside a guest and results in code execution with hypervisor privileges.

CVSS severity8.8
High
EPSS probability0.27%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds write in Toolgate in Parallels Desktop 16.1.3 (49160) allows guest OS users to execute arbitrary code in the hypervisor. Toolgate fails to validate guest-supplied data before writing it into an allocated buffer, permitting a write beyond the buffer boundary. Exploitation requires high-privileged code execution inside a guest and results in code execution with hypervisor privileges.

The record

CVE
CVE-2021-34857
Published
Oct 25, 2021
Updated
Aug 4, 2024
Vendor
Parallels
Product
Parallels Desktop
Classifications
CWE-787, T1068
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Oct 25, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=16.1.3 (49160)

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

Parallels · Parallels Desktopversion=16.1.3 (49160)

Published CVSS scores

4.6NIST NVDAV:L/AC:L/Au:N/C:P/I:P/A:P
8.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
8.2Zero Day InitiativeCVSS:3.0/AV:L/AC:L/PR:H/UI:N/S:C/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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1068Exploitation for Privilege Escalation

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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