CVE-2017-10923 in Xen
Summary
by MITRE
Xen through 4.8.x does not validate a vCPU array index upon the sending of an SGI, which allows guest OS users to cause a denial of service (hypervisor crash), aka XSA-225.
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Analysis
by VulDB Data Team • 12/30/2020
The vulnerability identified as CVE-2017-10923 represents a critical validation flaw in the Xen hypervisor version 4.8.x and earlier, specifically impacting the handling of software-generated interrupts within virtualized environments. This issue manifests when the hypervisor fails to properly validate the vCPU array index during the processing of SGI (Software Generated Interrupt) operations, creating a potential vector for malicious exploitation by unprivileged guest operating system users.
The technical implementation of this vulnerability stems from insufficient input validation within the hypervisor's interrupt handling mechanism. When a guest OS attempts to send an SGI to a specific virtual CPU, the hypervisor should verify that the target vCPU index falls within acceptable bounds of the allocated vCPU array. However, the absence of this validation check allows an attacker to specify an invalid or out-of-bounds vCPU index, which can trigger memory corruption or access violations within the hypervisor's memory management subsystem. This flaw directly maps to CWE-129, which describes improper validation of array indices, and specifically aligns with the ATT&CK technique T1068, which involves exploiting local privileges to execute malicious code.
The operational impact of this vulnerability extends beyond simple denial of service, as it represents a fundamental weakness in the hypervisor's security boundaries that could potentially be escalated to more severe consequences. When exploited, the vulnerability causes the hypervisor to crash or become unresponsive, effectively rendering all virtual machines hosted on that hypervisor unavailable until manual intervention occurs. This disruption affects not only individual guest operating systems but can compromise the entire virtualized infrastructure, particularly in cloud computing environments where multiple tenants share the same physical hardware. The vulnerability's severity is compounded by the fact that it requires minimal privileges to exploit, as guest OS users already possess the necessary permissions to send SGIs, making this attack vector particularly dangerous in multi-tenant cloud deployments.
Mitigation strategies for CVE-2017-10923 should prioritize immediate patching of affected Xen hypervisor versions to the patched releases that include proper index validation mechanisms. Organizations should implement comprehensive monitoring of hypervisor stability and performance metrics to detect potential exploitation attempts, as well as establish robust incident response procedures for handling hypervisor crashes. Additionally, virtualization administrators should consider implementing network segmentation and access controls to limit guest OS privileges where possible, though this approach provides only partial protection given that the vulnerability is inherent to the hypervisor's interrupt handling code. The vulnerability also underscores the importance of regular security assessments and penetration testing of virtualization environments to identify similar validation flaws that may exist in other components of the virtualized infrastructure stack.