CVE-2021-22017 in vCenter Server
Summary
by MITRE • 09/24/2021
Rhttproxy as used in vCenter Server contains a vulnerability due to improper implementation of URI normalization. A malicious actor with network access to port 443 on vCenter Server may exploit this issue to bypass proxy leading to internal endpoints being accessed.
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Analysis
by VulDB Data Team • 01/30/2025
The CVE-2021-22017 vulnerability represents a critical security flaw in VMware vCenter Server's rhttproxy component that exploits improper URI normalization implementation. This vulnerability resides within the HTTP proxy functionality that handles requests between external clients and internal vCenter Server endpoints. The flaw allows attackers to manipulate URI parsing mechanisms in ways that circumvent intended access controls and proxy restrictions. The vulnerability specifically affects the normalization process that should standardize URL formats before routing requests, but fails to properly handle certain URI sequences that can be crafted to bypass security boundaries.
The technical implementation of this vulnerability stems from insufficient validation of URI components during the normalization phase. When vCenter Server processes incoming requests through its rhttproxy module, the system fails to properly canonicalize certain URI sequences that contain encoded characters, directory traversal patterns, or malformed path components. This weakness enables attackers to craft requests that appear to target external endpoints while actually accessing internal vCenter Server components that should remain protected behind the proxy layer. The flaw operates at the application layer and leverages the HTTP protocol's handling of URL encoding and path resolution.
From an operational impact perspective, this vulnerability creates a significant risk for organizations relying on vCenter Server for virtual infrastructure management. Attackers can potentially access internal management interfaces, administrative functions, and sensitive configuration data that should only be reachable through authorized channels. The attack vector requires network access to port 443, which is the standard HTTPS port for vCenter Server, making it particularly dangerous in environments where this port is exposed to untrusted networks. Successful exploitation could lead to complete compromise of the virtualization infrastructure, data exfiltration, and potential lateral movement within the network.
Security professionals should prioritize patching this vulnerability through VMware's official security updates and ensure proper network segmentation to limit exposure. The mitigation strategy should include implementing network access controls that restrict direct access to vCenter Server ports, deploying intrusion detection systems to monitor for suspicious URI patterns, and conducting thorough network audits to identify any unauthorized access attempts. Organizations should also review their existing security configurations to ensure that proper access controls are in place to prevent similar URI normalization issues in other components. This vulnerability aligns with CWE-601 and ATT&CK techniques related to URL manipulation and privilege escalation through proxy bypass mechanisms.