CVE-2017-17564 in Xen
Summary
by MITRE
An issue was discovered in Xen through 4.9.x allowing guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging incorrect error handling for reference counting in shadow mode.
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Analysis
by VulDB Data Team • 01/17/2023
The vulnerability identified as CVE-2017-17564 represents a critical security flaw in the Xen hypervisor affecting versions through 4.9.x. This issue stems from improper error handling within the reference counting mechanism when operating in shadow page mode, creating a pathway for malicious guest operating system users to exploit the system. The flaw exists at the fundamental level of memory management within the hypervisor, where incorrect reference counting can lead to unpredictable behavior and potential privilege escalation. Such vulnerabilities are particularly dangerous because they exist at the hypervisor level, where guest users can directly influence host system operations and potentially compromise the entire virtualization environment.
The technical implementation of this vulnerability involves the shadow page mode functionality within Xen's memory management system. When guest operating systems manipulate memory references in specific ways, the hypervisor's reference counting logic fails to properly handle error conditions, leading to memory corruption or improper deallocation. This error handling failure can manifest in two primary ways: either causing a host system crash through memory corruption that results in a denial of service, or enabling privilege escalation where guest users can execute code with host-level privileges. The vulnerability specifically targets the shadow page tables that Xen uses to maintain memory mappings between guest and host systems, making it particularly dangerous in multi-tenant virtualization environments.
The operational impact of CVE-2017-17564 extends far beyond simple denial of service scenarios, as it can enable complete compromise of the host system. In cloud computing environments and virtualized infrastructure, this vulnerability could allow an attacker with access to a single guest VM to potentially gain control over the entire host system and all other VMs running on that host. This represents a severe violation of the fundamental security isolation principles that hypervisors are designed to maintain. The vulnerability can be exploited through carefully crafted memory operations that trigger the faulty reference counting logic, making it particularly insidious as it may not require sophisticated attack vectors beyond normal guest execution capabilities.
Mitigation strategies for this vulnerability involve immediate patching of Xen hypervisor installations to versions that address the reference counting error handling issues. Organizations should prioritize updating their Xen installations to versions 4.10.0 or later, which contain the necessary fixes for this specific vulnerability. Additionally, implementing monitoring systems to detect unusual memory access patterns and reference counting behaviors can help identify potential exploitation attempts. From a defense-in-depth perspective, virtualization administrators should consider implementing additional security measures such as hardware virtualization extensions, memory protection mechanisms, and regular security audits of virtualized environments. The vulnerability aligns with CWE-691, which covers insufficient control flow management, and maps to ATT&CK techniques involving privilege escalation and denial of service through hypervisor manipulation. Organizations should also review their incident response procedures to ensure preparedness for potential exploitation of this class of vulnerabilities in their virtualized infrastructures.