CVE-2011-2519 in Linux
Summary
by MITRE
Xen in the Linux kernel, when running a guest on a host without hardware assisted paging (HAP), allows guest users to cause a denial of service (invalid pointer dereference and hypervisor crash) via the SAHF instruction.
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Analysis
by VulDB Data Team • 01/18/2022
The vulnerability identified as CVE-2011-2519 represents a critical denial of service flaw within the Xen hypervisor implementation in Linux kernel environments. This issue specifically manifests when a guest operating system runs on a host system that lacks hardware assisted paging capabilities, creating a unique exploitation vector that can compromise system stability. The vulnerability stems from improper handling of the SAHF (Set AH Flag) instruction within the hypervisor's memory management subsystem, where guest users can manipulate this instruction to trigger invalid pointer dereferences that ultimately lead to hypervisor crashes.
The technical flaw occurs in the hypervisor's memory management routines when processing guest instructions without hardware assisted paging support. The SAHF instruction, which sets the flags register based on the lower 8 bits of the accumulator, becomes a critical attack vector when executed in guest contexts. When the hypervisor attempts to process this instruction in environments lacking HAP support, the memory management subsystem fails to properly validate or handle the instruction's effects on the processor state. This results in an invalid pointer dereference that causes the hypervisor to crash and subsequently terminate the virtual machine hosting the malicious guest.
The operational impact of this vulnerability extends beyond simple denial of service, as it can potentially disrupt critical virtualized environments and compromise the availability of services running within virtual machines. Attackers can exploit this weakness to repeatedly crash hypervisor instances, leading to system-wide service interruptions and potential data loss. The vulnerability is particularly concerning in cloud computing environments where multiple virtual machines share the same physical host, as a single compromised guest could affect the entire host system and all hosted virtual environments. Organizations relying on Xen virtualization platforms for infrastructure hosting face significant risk from this vulnerability, especially when running guests on hosts without hardware assisted paging capabilities.
Mitigation strategies for CVE-2011-2519 focus primarily on ensuring hardware assisted paging is enabled on host systems whenever possible, as this eliminates the vulnerable code path entirely. System administrators should implement regular patching schedules to ensure Xen hypervisor versions include fixes for this vulnerability, typically addressed through updates that properly validate guest instructions before processing them in memory management contexts. Additionally, monitoring systems should be deployed to detect unusual hypervisor crash patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-125, which addresses out-of-bounds read conditions, and relates to ATT&CK technique T1499.001 for network denial of service attacks. Organizations should also consider implementing guest isolation measures and monitoring for anomalous instruction execution patterns that could indicate exploitation attempts.