CVE-2018-19963 in Xen
Summary
by MITRE
An issue was discovered in Xen 4.11 allowing HVM guest OS users to cause a denial of service (host OS crash) or possibly gain host OS privileges because x86 IOREQ server resource accounting (for external emulators) was mishandled.
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Analysis
by VulDB Data Team • 04/19/2020
The vulnerability identified as CVE-2018-19963 represents a critical security flaw in the Xen hypervisor version 4.11 that affects the handling of x86 IOREQ server resource accounting mechanisms. This issue arises within the context of hardware virtualization where guest operating systems running under Xen can manipulate the hypervisor's resource management systems to cause unintended consequences. The problem specifically manifests in the interaction between the host hypervisor and external emulators that handle input/output requests from virtual machines, creating a scenario where guest users can exploit improper resource accounting to compromise system integrity.
The technical root cause of this vulnerability lies in the flawed resource accounting implementation within Xen's x86 IOREQ server subsystem. When HVM (Hardware Virtual Machine) guest operating systems make I/O requests that require external emulators, the hypervisor maintains accounting of these resources to prevent abuse and ensure fair allocation. However, the implementation contains a logic flaw that allows malicious guest users to manipulate this accounting mechanism, potentially leading to resource exhaustion or privilege escalation. The vulnerability stems from insufficient validation and proper resource management when external emulators process I/O requests from virtual machines, creating opportunities for exploitation that bypass normal security boundaries.
The operational impact of this vulnerability extends beyond simple denial of service conditions to encompass potential privilege escalation scenarios that could allow guest users to execute arbitrary code with host-level privileges. When exploited, the vulnerability can cause the host operating system to crash, effectively creating a denial of service condition that disrupts all virtual machines running on that hypervisor. More critically, the flaw may enable guest users to gain unauthorized access to host resources, potentially allowing them to escape the virtual machine sandbox and execute malicious code with elevated privileges. This represents a significant compromise of the fundamental security isolation that virtualization environments rely upon for protecting host systems from guest-based attacks.
Mitigation strategies for CVE-2018-19963 should focus on immediate patching of affected Xen hypervisor versions to address the resource accounting flaws in the IOREQ server implementation. Organizations should prioritize updating their Xen installations to versions that contain the appropriate fixes for this vulnerability, as the risk of exploitation increases with the presence of vulnerable systems in production environments. Additionally, implementing network segmentation and access controls can help limit the potential impact of exploitation by reducing the attack surface available to malicious guest users. The vulnerability aligns with CWE-362, which addresses concurrent execution using shared resource manipulation, and maps to ATT&CK technique T1055 for privilege escalation through hypervisor manipulation. Organizations should also consider implementing monitoring and logging mechanisms to detect anomalous resource usage patterns that may indicate exploitation attempts, as the vulnerability can be leveraged for both denial of service and privilege escalation attacks within virtualized environments.