CVE-2020-11635 in Client Connector
Summary
by MITRE • 02/16/2021
The Zscaler Client Connector prior to 3.1.0 did not sufficiently validate RPC clients, which allows a local adversary to execute code with system privileges or perform limited actions for which they did not have privileges.
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Analysis
by VulDB Data Team • 03/02/2021
The vulnerability identified as CVE-2020-11635 affects the Zscaler Client Connector software version 3.1.0 and earlier, presenting a critical security flaw that stems from insufficient validation of remote procedure call clients. This weakness creates a privilege escalation vector that enables local adversaries to execute arbitrary code with system-level privileges, effectively bypassing normal access controls and authorization mechanisms. The vulnerability resides in the client connector's RPC implementation where proper authentication and authorization checks are inadequate, allowing malicious processes to impersonate legitimate RPC clients.
The technical flaw manifests through improper input validation within the RPC communication layer of the Zscaler Client Connector. When the system processes remote procedure calls, it fails to adequately verify the identity and privileges of the calling client, creating an opportunity for privilege escalation attacks. This vulnerability operates under the broader category of privilege escalation flaws that are classified under CWE-264, specifically related to permissions, privileges, and access controls. The flaw allows an attacker with local system access to craft malicious RPC requests that the system accepts as legitimate, thereby executing code with elevated privileges.
From an operational standpoint, this vulnerability poses significant risks to organizations using Zscaler Client Connector as their primary security solution. Local adversaries who gain access to a system running the vulnerable software can leverage this flaw to escalate their privileges from standard user level to system administrator level, potentially gaining access to sensitive data, modifying system configurations, or establishing persistent backdoors. The impact extends beyond immediate privilege escalation as attackers can use the elevated privileges to perform actions such as installing malware, modifying firewall rules, accessing encrypted communications, or exfiltrating sensitive information. This vulnerability directly maps to ATT&CK technique T1068, which covers 'Local Privilege Escalation' and represents a critical weakness in the system's defense-in-depth strategy.
The exploitation of this vulnerability requires local system access, making it particularly concerning for environments where insider threats exist or where system compromise occurs through other attack vectors. Once an attacker achieves local access, they can leverage the RPC validation bypass to execute code with system privileges, potentially leading to complete system compromise. Organizations should consider implementing additional monitoring controls to detect unusual RPC activity and privilege escalation attempts, as well as establishing robust access control policies to limit local user privileges where possible. The vulnerability underscores the importance of proper input validation and authentication mechanisms in security software, particularly in components that handle remote procedure calls and privilege management. Remediation efforts should focus on updating to Zscaler Client Connector version 3.1.0 or later, which includes proper RPC client validation mechanisms and enhanced privilege controls.