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Client ConnectorApplication · Zscaler

CVE-2020-11633

CRITICAL · 9.8 CVSS v3.1 Published 2021-07-15
Fix available
A fix is available. Upgrade to 2.1.2.81 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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 for Windows prior to 2.1.2.74 had a stack based buffer overflow when connecting to misconfigured TLS servers. An adversary would potentially have been able to execute arbitrary 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

A stack-based buffer overflow vulnerability existed in Zscaler Client Connector for Windows versions prior to 2.1.2.74. The flaw was triggered when the client connected to misconfigured TLS servers, potentially allowing an attacker to execute arbitrary code with system-level privileges.

MitigationUpgrade Zscaler Client Connector for Windows to version 2.1.2.74 or later to remediate this 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:< 2.1.2.81

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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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. Locate Zscaler Client Connector installation
    Check for Zscaler Client Connector in Windows Program Files directory (typically C:\Program Files\Zscaler\) or check Add/Remove Programs for the installed application
    Affected if Zscaler Client Connector is installed on the system
  2. Retrieve installed version number
    Right-click the Zscaler Client Connector executable (often named ZscalerClientConnector.exe or similar), select Properties, and view the Details tab for the Version field. Alternatively, check the Windows Registry under HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\ for Zscaler entry or use 'wmic product get name,version' command
    Affected if Version cannot be determined or is lower than 2.1.2.81
  3. Compare version against affected range
    Compare the installed version number to the affected range: any version below 2.1.2.81 is vulnerable. Note that version 2.1.2.74 through 2.1.2.80 are also affected as the fix was released in 2.1.2.81
    Affected if Installed version is less than 2.1.2.81
  4. Verify TLS client functionality is active
    Confirm the Zscaler Client Connector service is running and the client has network connectivity. The vulnerability triggers when the client connects to misconfigured TLS servers, so active usage of the client increases exposure
    Affected if The Zscaler Client Connector service is enabled and actively processing TLS connections

The system is affected if Zscaler Client Connector for Windows is installed with a version lower than 2.1.2.81 and the client is actively used or capable of connecting to TLS servers.

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 2.1.2.81 or later
Fixed in 2.1.2.81
Interim mitigation

Upgrade Zscaler Client Connector for Windows to version 2.1.2.74 or later to remediate this vulnerability.

Recommended fix High confidence

Zscaler Client Connector 2.1.2.81 or later (minimum fixed version 2.1.2.74)

  1. 1. Verify current Zscaler Client Connector version by opening the application and checking About/Help section, or via Control Panel > Programs and Features
  2. 2. Download the latest Zscaler Client Connector for Windows from the official Zscaler portal or help.zscaler.com
  3. 3. Ensure you have administrator privileges on the Windows machine
  4. 4. Close any applications that may interfere with the installation
  5. 5. Run the installer and follow the on-screen prompts to upgrade
  6. 6. After installation, restart the system if prompted
  7. 7. Verify the new version is installed (should be 2.1.2.81 or later)
Caveat Standard upgrade; ensure compatibility with your Zscaler service subscription

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

Fix this in Client Connector Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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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-2020-11633 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