CVE-2026-59570: Zscaler Client Connector Privilege Escalation

CVE-2026-59570 Overview

CVE-2026-59570 affects Zscaler Client Connector on endpoints where a pre-installed peer application can interact with the connector without adequate validation. An attacker with local, low-privileged access through a co-resident app can tear down the Zscaler tunnel, force user logout, and toggle packet capture. The flaw is classified as improper input validation [CWE-20] and carries a scope change, meaning impact extends beyond the vulnerable component to the wider protected environment. Successful exploitation removes secure web gateway protection from the endpoint and disrupts controlled network egress for the user session.

Critical Impact
A local peer application can disable Zscaler tunnel enforcement, log the user out of the client, and manipulate packet capture state, breaking egress controls and enabling unmonitored traffic.

Affected Products

Zscaler Client Connector (affected versions per vendor release summary)
Deployments where third-party or pre-installed peer applications share the endpoint
Windows and macOS endpoints running vulnerable Client Connector builds

Discovery Timeline

2026-09-14 - CVE-2026-59570 published to the National Vulnerability Database (NVD)
2026-09-18 - Last updated in NVD database

Technical Details for CVE-2026-59570

Vulnerability Analysis

Zscaler Client Connector exposes local control interfaces used by supporting components on the host. On affected versions, the connector does not sufficiently validate requests originating from peer applications installed on the same system. A local process with low privileges can invoke privileged tunnel management actions that should be restricted to trusted components.

The operational impact spans three actions. First, the attacker tears down the active Zscaler tunnel, removing the security layer that inspects and controls outbound traffic. Second, the attacker forces user logout from the client, requiring re-authentication and breaking session continuity. Third, the attacker toggles packet capture, which can be enabled to record sensitive traffic or disabled to hide subsequent activity.

Root Cause

The root cause is improper input validation on the local interface that accepts control commands from peer applications. Trust decisions rely on the identity or presence of a co-installed application rather than strong authentication of the caller and the request. Any pre-installed peer application meeting the flawed trust check can issue high-impact commands.

Attack Vector

Exploitation requires local access with low privileges on the endpoint. The attacker must operate through, or masquerade as, a pre-installed peer application recognized by the Client Connector. No user interaction is required. The high attack complexity reflects the need for a suitable peer application context and the specific conditions under which the connector accepts the request. Because scope changes, the impact reaches the enterprise network posture rather than only the connector process.

No public proof-of-concept exploit is listed for CVE-2026-59570, and it is not present in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2026-59570

Indicators of Compromise

Unexpected Zscaler tunnel state transitions to disconnected without user or administrator action.
Forced logouts or repeated re-authentication prompts in Zscaler Client Connector logs.
Packet capture toggled on or off outside of scheduled troubleshooting windows.
Local processes not owned by Zscaler invoking Client Connector control interfaces.

Detection Strategies

Correlate endpoint process telemetry with Zscaler tunnel state changes to identify non-Zscaler processes preceding a disconnect.
Alert on invocations of Client Connector control paths by unsigned or unexpected binaries on managed endpoints.
Compare Zscaler cloud-side session termination events against endpoint-side initiators to spot local-only tunnel teardowns.

Monitoring Recommendations

Ship Zscaler Client Connector logs to a central analytics platform and track tunnel up/down, logout, and packet capture events.
Baseline the set of processes that legitimately interact with the connector and flag deviations.
Monitor for privilege changes or new persistence by pre-installed peer applications on user endpoints.

How to Mitigate CVE-2026-59570

Immediate Actions Required

Inventory endpoint versions of Zscaler Client Connector and identify hosts running affected builds.
Upgrade Zscaler Client Connector to a fixed version as listed in the vendor release summary.
Restrict installation of untrusted peer applications on endpoints running the connector.
Enforce Zscaler tamper protection and administrator password requirements for client actions where supported.

Patch Information

Zscaler addresses this issue in updated Client Connector releases documented in the Zscaler Client Connector Release Summary. Administrators should review the release notes to identify the first fixed version applicable to their deployment channel and schedule staged rollout to all managed endpoints.

Workarounds

Limit local administrative rights and control which peer applications may be installed alongside Client Connector.
Enable tamper protection settings in Zscaler Client Connector policy to require credentials for disabling protection.
Use application allowlisting to prevent execution of unapproved processes that could invoke connector control interfaces.

bash

# Configuration example
# Verify installed Zscaler Client Connector version on Windows
reg query "HKLM\SOFTWARE\Zscaler Inc.\Zscaler Client Connector" /v ProductVersion

# Verify installed Zscaler Client Connector version on macOS
defaults read /Applications/Zscaler/Zscaler.app/Contents/Info.plist CFBundleShortVersionString