CVE-2016-5331 in ESXi Server
Summary
by MITRE
CRLF injection vulnerability in VMware vCenter Server 6.0 before U2 and ESXi 6.0 allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks via unspecified vectors.
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Analysis
by VulDB Data Team • 03/21/2019
The CVE-2016-5331 vulnerability represents a critical CRLF injection flaw affecting VMware vCenter Server 6.0 before patch level U2 and ESXi 6.0 systems. This vulnerability resides within the HTTP response handling mechanisms of VMware's virtualization management platform, specifically targeting the way the software processes user-supplied input in HTTP headers. The flaw enables remote attackers to inject carriage return line feed sequences that can manipulate HTTP responses, creating a pathway for sophisticated attack vectors that extend beyond simple header manipulation.
The technical exploitation of this vulnerability stems from inadequate input validation and sanitization within the web server components of VMware's infrastructure management tools. When user-controllable data is improperly processed and included in HTTP response headers without proper encoding or filtering, attackers can insert CRLF sequences that break out of the intended header context. This creates a condition where malicious input can inject additional HTTP headers or manipulate existing response structures, fundamentally compromising the integrity of HTTP communications between clients and the vulnerable VMware systems.
From an operational perspective, this vulnerability poses significant risks to enterprise environments relying on VMware vCenter Server for virtual infrastructure management. Attackers leveraging this flaw can execute HTTP response splitting attacks that enable various malicious activities including session hijacking, cross-site scripting exploitation, cache poisoning, and transparent proxy attacks. The impact extends beyond immediate credential theft to potentially allowing attackers to redirect users to malicious sites or manipulate web content delivered to legitimate users, creating a persistent threat vector within the organization's network infrastructure.
The vulnerability aligns with CWE-113, which specifically addresses "Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting')", and maps to several ATT&CK techniques including T1190 for Exploit Public-Facing Application and T1071.1002 for Application Layer Protocol: Web Protocols. Organizations utilizing affected VMware products face potential compromise of their virtualized environments, with attackers able to manipulate management interfaces and potentially gain elevated privileges within the virtual infrastructure. The attack surface is particularly concerning given that vCenter Server serves as the central management point for VMware environments, making successful exploitation potentially devastating for enterprise security posture.
Mitigation strategies for CVE-2016-5331 should prioritize immediate patch application to VMware vCenter Server 6.0 U2 and ESXi 6.0 releases that address the underlying input validation issues. Network segmentation and web application firewalls should be implemented to monitor and filter HTTP traffic for suspicious CRLF sequences, while comprehensive logging and monitoring of HTTP response headers can help detect exploitation attempts. Security teams should also conduct thorough vulnerability assessments of their VMware environments and implement strict input validation policies across all web-facing components to prevent similar vulnerabilities from emerging in other system components.