CVE-2021-33907

Elevated code execution via MSI signature bypass

Published Sep 27, 2021 · Updated Aug 4, 2024

Improper certificate validation in Zoom Client for Meetings for Windows before 5.3.0 allows local users to execute code during updates. The Windows updater accepts an MSI package without properly validating the certificate information used to sign it. A local user must trigger an update that a victim accepts; the package then runs in an elevated privileged context and can compromise the host.

CVSS severity9.8
Critical
EPSS probability2.96%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate validation in Zoom Client for Meetings for Windows before 5.3.0 allows local users to execute code during updates. The Windows updater accepts an MSI package without properly validating the certificate information used to sign it. A local user must trigger an update that a victim accepts; the package then runs in an elevated privileged context and can compromise the host.

The record

CVE
CVE-2021-33907
Published
Sep 27, 2021
Updated
Aug 4, 2024
Vendor
Zoom Video Communications, Inc.
Product
Zoom Client for Meetings for Windows
Classifications
CWE-295, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 27, 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=All versions of the Zoom Client for Meetings for Windows before version 5.3.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Zoom Video Communications, Inc. · Zoom Client for Meetings for Windowsversion=All versions of the Zoom Client for Meetings for Windows before version 5.3.0

Published CVSS scores

9.8NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
10.0NIST National Vulnerability DatabaseAV:N/AC:L/Au:N/C:C/I:C/A:C

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-295Improper Certificate Validation
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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