CVE-2010-4255 in Xen
Summary
by MITRE
The fixup_page_fault function in arch/x86/traps.c in Xen 4.0.1 and earlier on 64-bit platforms, when paravirtualization is enabled, does not verify that kernel mode is used to call the handle_gdt_ldt_mapping_fault function, which allows guest OS users to cause a denial of service (host OS BUG_ON) via a crafted memory access.
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Analysis
by VulDB Data Team • 10/13/2021
The vulnerability identified as CVE-2010-4255 represents a critical flaw in the Xen hypervisor's memory management subsystem that specifically affects 64-bit platforms with paravirtualization enabled. This issue resides within the fixup_page_fault function located in arch/x86/traps.c, where the hypervisor fails to properly validate the execution context when handling certain memory access patterns. The flaw allows malicious guest operating systems to exploit a missing validation check that should ensure kernel mode execution before invoking the handle_gdt_ldt_mapping_fault function. This oversight creates a privilege escalation path that can be leveraged to trigger a BUG_ON condition in the host operating system, effectively causing a system crash or denial of service that impacts the entire virtualized environment.
The technical nature of this vulnerability stems from improper privilege validation within the hypervisor's fault handling mechanism. When a guest OS attempts a specific memory access pattern, the Xen hypervisor's page fault handler fails to verify that the call originates from kernel mode before proceeding with sensitive operations. This validation gap creates a condition where guest users can manipulate the execution flow to force the host kernel into an unexpected state. The handle_gdt_ldt_mapping_fault function, which is responsible for managing global descriptor table and local descriptor table mappings, becomes accessible through an unvalidated path that bypasses normal privilege checks. This flaw directly relates to CWE-284, which addresses improper access control, and demonstrates how insufficient privilege validation can lead to system instability and potential denial of service conditions.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the integrity of the entire virtualized infrastructure. When exploited, the vulnerability can cause the host operating system to enter an unrecoverable state through the BUG_ON macro, which is designed to catch programming errors and system inconsistencies. This type of exploitation can result in complete system crashes that affect all virtual machines running on the compromised hypervisor, potentially causing widespread service outages. The vulnerability affects all versions of Xen up to and including 4.0.1, making it particularly concerning for organizations that may have legacy systems or delayed patch adoption. Attackers can leverage this flaw to perform persistent denial of service attacks against virtualized environments without requiring elevated privileges within the guest operating systems.
Mitigation strategies for CVE-2010-4255 primarily focus on immediate patch deployment and system hardening measures. The most effective solution involves upgrading to Xen version 4.0.2 or later, which includes the necessary validation checks to prevent unauthorized access to the handle_gdt_ldt_mapping_fault function. Organizations should also implement monitoring solutions to detect anomalous memory access patterns that might indicate exploitation attempts. Network segmentation and isolation of virtualized environments can help limit the potential impact of successful attacks, while regular vulnerability assessments should be conducted to identify similar privilege escalation paths. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, specifically targeting the 'Exploitation for Privilege Escalation' tactic, where attackers leverage hypervisor flaws to gain unauthorized access to system resources. System administrators should also consider implementing additional logging and alerting mechanisms to detect when BUG_ON conditions are triggered, as these events often indicate successful exploitation attempts.