CVE-2017-4940 in ESXi
Summary
by MITRE
The ESXi Host Client in VMware ESXi (6.5 before ESXi650-201712103-SG, 5.5 before ESXi600-201711103-SG and 5.5 before ESXi550-201709102-SG) contains a vulnerability that may allow for stored cross-site scripting (XSS). An attacker can exploit this vulnerability by injecting Javascript, which might get executed when other users access the Host Client.
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Analysis
by VulDB Data Team • 01/27/2021
The vulnerability identified as CVE-2017-4940 represents a critical stored cross-site scripting flaw within VMware ESXi Host Client interfaces. This security weakness affects multiple versions of VMware ESXi including 6.5 before specific patch levels and 5.5 before their respective security updates. The flaw resides in the Host Client component which serves as the primary management interface for ESXi hosts, making it a prime target for attackers seeking to compromise virtualized environments. The vulnerability stems from insufficient input validation and output encoding mechanisms within the client-side processing of user-supplied data, creating an environment where malicious scripts can be persistently stored and subsequently executed.
The technical exploitation of this vulnerability occurs when an attacker successfully injects malicious JavaScript code into the Host Client interface through vulnerable input fields or parameters. This stored payload remains persistent within the application's data storage, waiting for unsuspecting users to access the affected interface. When other administrators or users navigate to pages containing the malicious content, the injected JavaScript executes in their browser context, potentially leading to complete session hijacking, credential theft, or further exploitation of the compromised system. The vulnerability specifically targets the Host Client's handling of user-provided data without proper sanitization, aligning with CWE-79 which defines cross-site scripting vulnerabilities as improper handling of untrusted data.
The operational impact of CVE-2017-4940 extends beyond simple script execution, as it provides attackers with a persistent foothold within virtualized environments. Attackers can leverage this vulnerability to establish backdoors, steal administrative credentials, or manipulate virtual machine configurations through the compromised Host Client interface. The persistence aspect of stored XSS makes this particularly dangerous as the malicious code continues to execute whenever users access the affected interface, potentially going unnoticed for extended periods. This vulnerability directly impacts the security posture of VMware environments by undermining the integrity of the management interface, which is critical for maintaining proper virtual infrastructure control and monitoring.
Organizations affected by this vulnerability should immediately apply the recommended security patches provided by VMware, specifically targeting the ESXi versions mentioned in the advisory. The patching process requires careful planning and execution to avoid service disruption while ensuring complete remediation. Network segmentation and access controls should be implemented to limit exposure of the Host Client interface to trusted users only, reducing the attack surface for potential exploitation. Security monitoring should be enhanced to detect unusual activity patterns that might indicate exploitation attempts, including monitoring for suspicious script injections or unauthorized access to management interfaces. According to ATT&CK framework, this vulnerability maps to T1059.007 for script execution and T1566 for credential access, highlighting the multi-faceted attack vectors possible through this flaw. Regular security assessments and penetration testing should be conducted to identify similar vulnerabilities in other management interfaces and applications within the virtualized environment.