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Client ConnectorApplication · Zscaler

CVE-2021-26734

MEDIUM · 5.5 CVSS v3.1 Published 2023-10-23
Fix available
A fix is available. Upgrade to 3.4.0.124 or later.
See remediation →
58/100
Remediation priority · Elevated
No privileges

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
Zscaler Client Connector Installer on Windows before version 3.4.0.124 improperly handled directory junctions during uninstallation. A local adversary may be able to delete folders in an elevated context.

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

The Zscaler Client Connector Installer for Windows versions prior to 3.4.0.124 improperly handled directory junctions (Windows directory symbolic links) during the uninstallation process. This allowed a local attacker to manipulate junction points to cause the elevated uninstaller to delete arbitrary folders outside the intended installation directory, leading to potential privilege escalation via arbitrary file deletion.

MitigationUpgrade Zscaler Client Connector Installer to version 3.4.0.124 or later, which contains the proper handling of directory junctions during uninstallation.

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
Client ConnectorApplication
Affected:< 3.4.0.124

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
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

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 Zscaler Client Connector is installed
    Check for the presence of Zscaler Client Connector in the system registry under HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall or use 'Get-WmiObject Win32_Product' (PowerShell) or review installed programs in Programs and Features
    Affected if The software is found to be installed on the system
  2. Determine the installed version of Zscaler Client Connector
    Retrieve the version information from the registry key for Zscaler Client Connector or by running 'Get-ItemProperty' on the installation directory if located, or using 'wmic product where "name like '%Zscaler%'" get version
    Affected if A version number is returned from the system
  3. Compare installed version against the affected range
    Compare the discovered version number to 3.4.0.124 using standard version comparison
    Affected if The installed version is lower than 3.4.0.124 (for example, 3.4.0.100 or any 3.x.x.x version below 3.4.0.124)
  4. Confirm the uninstaller vulnerability condition exists
    Since the flaw specifically affects the uninstallation process and the directory junction handling, if the product is installed with a version below 3.4.0.124, the vulnerable uninstaller code is present on the system
    Affected if The product version is below 3.4.0.124 and the uninstaller is present

The environment is affected if Zscaler Client Connector is installed with any version lower than 3.4.0.124, as this version range contains the vulnerable uninstaller with improper directory junction handling.

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
Upgrade available Upgrade to 3.4.0.124 or later
Fixed in 3.4.0.124
Interim mitigation

Upgrade Zscaler Client Connector Installer to version 3.4.0.124 or later, which contains the proper handling of directory junctions during uninstallation.

Recommended fix High confidence

Zscaler Client Connector 3.4.0.124 or later for Windows

  1. Verify the current installed version of Zscaler Client Connector by opening Control Panel > Programs and Features, or by running 'Get-ItemProperty HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\* | Where-Object {$_.DisplayName -like '*Zscaler*'} | Select-Object DisplayName, DisplayVersion' in PowerShell
  2. Navigate to the official Zscaler support portal at help.zscaler.com and download the Zscaler Client Connector version 3.4.0.124 or later for Windows
  3. Run the installer as an administrator and follow the on-screen prompts to complete the upgrade
  4. Verify the new version is installed correctly by checking the version again through Control Panel or the Zscaler Client Connector application

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

Fix this in Client Connector Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.

Scan for this in your stack

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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-2021-26734 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