CVE-2017-8903 in Xen
Summary
by MITRE
Xen through 4.8.x on 64-bit platforms mishandles page tables after an IRET hypercall, which might allow PV guest OS users to execute arbitrary code on the host OS, aka XSA-213.
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Analysis
by VulDB Data Team • 12/06/2022
The vulnerability identified as CVE-2017-8903 represents a critical security flaw in the Xen hypervisor affecting versions 4.8.x and earlier on 64-bit platforms. This issue stems from improper handling of page tables following an IRET hypercall operation, creating a privilege escalation vector that allows malicious guest operating systems to execute arbitrary code on the host system. The vulnerability specifically impacts Paravirtualized (PV) guest operating systems running on Xen hypervisors, making it particularly concerning for cloud environments and virtualized infrastructures where multiple tenants share the same physical hardware.
The technical root cause of this vulnerability lies in the hypervisor's failure to properly validate and manage memory page table entries during the IRET (Interrupt Return) hypercall execution. When a guest OS issues an IRET instruction, the hypervisor must correctly update the page table mappings to ensure proper memory access controls between the guest and host environments. In affected versions, the hypervisor incorrectly processes these page table modifications, leading to potential memory corruption and unauthorized code execution privileges. This flaw operates at the kernel level within the hypervisor's memory management subsystem and is classified under CWE-119 as a weakness related to memory safety and improper access control.
The operational impact of CVE-2017-8903 is severe and far-reaching across virtualized environments, as it enables a privilege escalation attack that can compromise the entire host system. An attacker controlling a guest OS can leverage this vulnerability to gain elevated privileges and execute malicious code with host-level permissions, potentially leading to complete system compromise. This vulnerability is particularly dangerous in cloud computing scenarios where multiple virtual machines share the same physical host, as it could allow one tenant to access or manipulate resources belonging to other tenants. The attack vector is relatively straightforward, requiring only that a malicious guest OS be able to execute an IRET hypercall with specific parameters, making it a significant concern for any organization relying on Xen-based virtualization technologies.
Mitigation strategies for CVE-2017-8903 primarily involve immediate patching of affected Xen hypervisor versions to the patched releases that address the page table handling issue. Organizations should prioritize updating their Xen installations to versions 4.8.1 or later, which contain the necessary fixes for this vulnerability. Additionally, implementing network segmentation and access controls can help limit the potential impact if exploitation occurs. The vulnerability aligns with ATT&CK technique T1055 for privilege escalation and T1068 for local privilege escalation, making it a significant concern for security operations teams monitoring for suspicious activity in virtualized environments. Regular security assessments and monitoring for anomalous behavior in hypervisor memory management should be implemented as part of comprehensive security posture management to detect potential exploitation attempts.