dbcve.org
Client ConnectorApplication · Zscaler

CVE-2021-26735

HIGH · 7.8 CVSS v3.1 Published 2023-10-23
Fix available
A fix is available. Upgrade to 3.6 or later.
See remediation →
81/100
Remediation priority · High
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
The Zscaler Client Connector Installer and Unsintallers for Windows prior to 3.6 had an unquoted search path vulnerability. A local adversary may be able to execute code with SYSTEM privileges.

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 and Uninstallers for Windows versions prior to 3.6 contain an unquoted search path vulnerability. This occurs when the application's executable path contains spaces and is not enclosed in quotes, allowing a local attacker to place a malicious executable in an intermediate directory that gets executed with SYSTEM privileges during installation or uninstallation.

MitigationUpgrade Zscaler Client Connector to version 3.6 or later to resolve the unquoted service path vulnerability.

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:< 3.6

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
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify if Zscaler Client Connector is installed
    Open Control Panel > Programs and Features, or run 'Get-WmiObject -Class Win32_Product' or check registry at HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall for an entry named 'Zscaler Client Connector'
    Affected if The software is listed in installed programs
  2. Check the installed version number
    In Programs and Features, click on Zscaler Client Connector to view the version, or run 'reg query HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall\{product GUID} /v DisplayVersion'
    Affected if The displayed version is lower than 3.6 (e.g., 3.5.x, 3.4.x, etc.)
  3. Locate the Zscaler service executable path
    Open Command Prompt as Administrator and run 'sc qc ZscalerClientConnector' (service name may vary - check for any Zscaler-related service with 'sc queryex type= service state= all | findstr Zscaler')
    Affected if The BINPATH or other path fields in the service configuration display an executable path that contains spaces and is not enclosed in quotation marks
  4. Check the installer and uninstaller paths in registry
    Run 'reg query HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall\{GUID} /v InstallLocation' and check the UninstallString for paths with spaces not in quotes
    Affected if The paths contain spaces and are not wrapped in quotes

A user is affected if Zscaler Client Connector version 3.6 or later is NOT installed AND the executable paths for the service, installer, or uninstaller contain unquoted spaces.

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 3.6 or later
Fixed in 3.6
Interim mitigation

Upgrade Zscaler Client Connector to version 3.6 or later to resolve the unquoted service path vulnerability.

Recommended fix High confidence

Client Connector 3.6 for Windows

  1. Navigate to the Zscaler Client Connector download page at help.zscaler.com
  2. Download the latest Zscaler Client Connector version 3.6 or later for Windows
  3. Close all running applications and ensure you have administrator privileges
  4. Run the Client Connector installer (e.g., ZscalerClientConnectorSetup-3.6.exe)
  5. Follow the installation wizard prompts to complete the upgrade
  6. Verify the installed version by checking Help > About in the Client Connector application
  7. Ensure the upgraded Client Connector is running and connected to your Zscaler account

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

Fix this in Client Connector Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.

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-2021-26735 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