CVE-2021-34420Public exploitNetwork attack vector

Code execution via unsigned installer scripts

Published Nov 11, 2021 · Updated Sep 16, 2024

Signature verification bypass in Zoom Client for Meetings for Windows before 5.5.4 allows remote attackers to execute code via a crafted installer. Installer.exe applies WinVerifyTrust only to PE files extracted from Zoom.msi, then processes unsigned .bat and .ps1 files and ZoomInstall.xml instructions. Exploitation requires a user to download, extract, and run the signed installer, after which embedded scripts execute with that user's privileges.

CVSS severity4.7
Medium
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Signature verification bypass in Zoom Client for Meetings for Windows before 5.5.4 allows remote attackers to execute code via a crafted installer. Installer.exe applies WinVerifyTrust only to PE files extracted from Zoom.msi, then processes unsigned .bat and .ps1 files and ZoomInstall.xml instructions. Exploitation requires a user to download, extract, and run the signed installer, after which embedded scripts execute with that user's privileges.

The record

CVE
CVE-2021-34420
Published
Nov 11, 2021
Updated
Sep 16, 2024
Vendor
Zoom Video Communications, Inc.
Product
Zoom Client for Meetings for Windows
Classifications
CWE-347, T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 11, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 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=unspecified <5.5.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Zoom Video Communications, Inc. · Zoom Client for Meetings for Windowsversion=unspecified <5.5.4

Published CVSS scores

4.7Zoom Video Communications, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
7.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:H/A:N

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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature
T1204.002Malicious File

Public exploit references

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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