CVE-2017-4928 in vSphere Web Client
Summary
by MITRE
The flash-based vSphere Web Client (6.0 prior to 6.0 U3c and 5.5 prior to 5.5 U3f) i.e. not the new HTML5-based vSphere Client, contains SSRF and CRLF injection issues due to improper neutralization of URLs. An attacker may exploit these issues by sending a POST request with modified headers towards internal services leading to information disclosure.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 01/24/2021
The vulnerability identified as CVE-2017-4928 affects the legacy flash-based vSphere Web Client version 6.0 prior to 6.0 U3c and 5.5 prior to 5.5 U3f, representing a critical security flaw in VMware's virtualization management interface. This vulnerability specifically targets the older flash-based client implementation rather than the newer HTML5-based vSphere Client, highlighting the continued risks associated with legacy components in enterprise environments. The affected systems typically operate within data center environments where vSphere manages virtualized infrastructure, making these systems prime targets for attackers seeking to exploit authentication bypasses and information disclosure vulnerabilities.
The technical flaw stems from improper neutralization of URLs within the vSphere Web Client's processing logic, creating conditions where Server-Side Request Forgery (SSRF) and CRLF injection attacks can be successfully executed. The vulnerability manifests when the application fails to properly validate and sanitize user-supplied input in HTTP headers, particularly those containing URL parameters or redirect specifications. This inadequate input validation allows attackers to craft malicious POST requests that manipulate internal service communications, effectively bypassing normal network security controls. The vulnerability maps directly to CWE-93, which specifically addresses improper neutralization of CRLF characters, and CWE-918, which covers server-side request forgery vulnerabilities. These weaknesses enable attackers to construct requests that can access internal services that would normally be restricted from external access.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with potential access to internal network resources and sensitive system information. When exploited successfully, attackers can leverage the SSRF capabilities to probe internal services, potentially discovering additional vulnerabilities within the network infrastructure. The CRLF injection component allows for manipulation of HTTP responses, which could lead to session hijacking, cross-site scripting attacks, or other malicious activities that compromise the integrity of the vSphere management environment. This vulnerability particularly affects organizations that maintain legacy vSphere installations, as these systems often continue to operate without the latest security updates, creating persistent attack vectors for threat actors.
Organizations should implement immediate mitigations including updating to the patched versions of vSphere 6.0 U3c and 5.5 U3f, which address the URL neutralization issues in the flash-based client. Network segmentation and firewall rules should be implemented to restrict access to internal vSphere services from external networks, while monitoring systems should be configured to detect anomalous HTTP request patterns that might indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1190, which covers exploit for client execution, and T1071.004, which covers application layer protocol: DNS, demonstrating how attackers can leverage these flaws to gain unauthorized access to internal systems. Security teams should also consider disabling the legacy flash-based vSphere Web Client entirely in favor of the newer HTML5-based interface, which has been designed with improved security controls and input validation mechanisms to prevent similar vulnerabilities from occurring in the future.