CVE-2026-59566 in Client Connector
Summary
by MITRE • 08/24/2026
A locally exploitable buffer overflow bug can cause a local denial-of-service attack on affected versions of Zscaler Client Connector on Android and ChromeOS.
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Analysis
by VulDB Data Team • 08/24/2026
The identified vulnerability represents a critical security flaw within the Zscaler Client Connector application, specifically affecting deployments on Android and ChromeOS operating systems. This issue stems from improper boundary checks during memory management operations, leading to a classic buffer overflow condition. In software engineering terms, this occurs when an application writes more data to a fixed-length block of memory than it can hold, causing the excess data to overwrite adjacent memory locations. Because this vulnerability is locally exploitable, it requires an attacker who has already gained access to the device or user session where the Zscaler Client Connector is running. This typically implies that physical access to the unattended device or a compromised local account with sufficient privileges to execute arbitrary code within the application context would be necessary for exploitation.
From a technical perspective, the buffer overflow allows an attacker to manipulate the control flow of the program by overwriting critical data structures such as return addresses or function pointers on the stack or heap. While many buffer overflow vulnerabilities are leveraged to achieve remote code execution and full system compromise, in this specific instance, the primary observable outcome is a denial-of-service condition. The corruption of memory leads to application instability, resulting in crashes or freezes that prevent legitimate users from accessing network resources protected by Zscaler Zero Trust Exchange policies. This disruption effectively breaks the security perimeter for the affected device, as the client agent ceases to function correctly and may fail to enforce traffic routing rules through the secure tunnel.
The operational impact of this vulnerability is significant despite its local nature. For enterprise environments relying on continuous visibility and control over endpoint connectivity, a denial-of-service attack against the security agent creates a blind spot in network monitoring. If an insider threat actor or a malicious process running under a user account triggers this overflow, it can disrupt business operations by severing secure connections without necessarily stealing data directly through code execution. Furthermore, repeated crashes may trigger automatic restarts of the client service, consuming system resources and potentially causing performance degradation on resource-constrained devices such as mobile phones or thin clients. This aligns with CWE-120, which classifies buffer copy without checking size limits as a fundamental memory safety error that undermines application integrity.
In terms of threat modeling, this vulnerability maps to the ATT&CK technique T1499, Endpoint Denial of Service, specifically under sub-techniques involving resource exhaustion or service disruption via software vulnerabilities. It also relates to CWE-787, which covers out-of-bounds write access that can lead to arbitrary code execution in more severe cases, although here the impact is limited to availability. The local exploitability vector means it falls under privilege requirements where a lower privileged user can affect system stability, highlighting risks associated with multi-user environments or shared workstations where one compromised account could disrupt security controls for others.
Mitigation strategies must focus on both immediate remediation and long-term defensive posture improvements. Organizations should prioritize applying the latest patches provided by Zscaler to update the Client Connector software across all affected Android and ChromeOS endpoints. Automated patch management systems can help ensure timely deployment of these fixes, reducing the window of exposure. Additionally, implementing strict application whitelisting policies using tools like Google Play Protect on Android or Enterprise DPC configurations on ChromeOS can prevent unauthorized applications from executing code that might trigger this vulnerability. Security teams should also monitor for unusual spikes in process crashes or service restarts associated with the Zscaler agent, which could indicate an ongoing exploitation attempt. Regular audits of local user privileges and enforcement of least-privilege principles will further limit the attack surface available to potential local attackers seeking to disrupt security services.