CVE-2018-7541 in Xen
Summary
by MITRE
An issue was discovered in Xen through 4.10.x allowing guest OS users to cause a denial of service (hypervisor crash) or gain privileges by triggering a grant-table transition from v2 to v1.
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Analysis
by VulDB Data Team • 02/16/2023
The vulnerability identified as CVE-2018-7541 represents a critical flaw in the Xen hypervisor affecting versions through 4.10.x that enables guest operating system users to exploit a grant-table transition mechanism. This issue stems from inadequate validation during the process of transitioning grant tables from version 2 to version 1, creating a potential pathway for malicious guest users to manipulate hypervisor memory management structures. The grant-table mechanism serves as a fundamental component for sharing memory pages between guest operating systems and the hypervisor, making this vulnerability particularly dangerous as it directly impacts the core virtualization infrastructure.
The technical implementation of this vulnerability involves a specific transition scenario within the grant-table handling code where guest users can manipulate the grant-table versioning system to force an improper transition from v2 to v1. This transition occurs without proper boundary checks or validation of the underlying data structures, allowing attackers to craft malicious grant table entries that trigger memory corruption within the hypervisor. The flaw essentially creates a condition where guest users can manipulate the hypervisor's internal state through carefully constructed grant table operations, bypassing normal access controls and memory protection mechanisms. This type of vulnerability falls under CWE-129, which addresses improper validation of array indices, and specifically relates to improper handling of grant table version transitions.
The operational impact of CVE-2018-7541 extends beyond simple denial of service scenarios to include potential privilege escalation capabilities that could allow guest users to execute arbitrary code within the hypervisor context. When exploited successfully, this vulnerability can cause hypervisor crashes that result in complete system downtime, affecting all virtual machines hosted on the compromised hypervisor. Additionally, the privilege escalation aspect means that attackers could potentially gain administrative access to the hypervisor itself, undermining the fundamental security isolation that virtualization environments are designed to provide. The attack vector is particularly concerning because it requires only guest user privileges to execute, making it accessible to any user running within a virtual machine that shares the same hypervisor instance.
Mitigation strategies for this vulnerability involve immediate patching of affected Xen hypervisor versions to address the grant-table transition logic and implement proper validation checks. System administrators should prioritize updating to Xen version 4.11 or later where this vulnerability has been resolved through enhanced grant table handling mechanisms. The fix typically involves adding proper bounds checking and validation routines during grant table version transitions to prevent malicious manipulation of the internal hypervisor data structures. Organizations should also implement monitoring solutions to detect unusual grant table operations and consider isolating critical virtual machines through additional security measures. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and denial of service, specifically targeting the hypervisor layer and exploiting weaknesses in virtualization management systems. The remediation process should include comprehensive testing of patched systems to ensure that the fix does not introduce regressions in legitimate grant table operations while maintaining the security posture of the virtualized environment.