CVE-2022-26356 in Xen
Summary
by MITRE • 04/05/2022
Racy interactions between dirty vram tracking and paging log dirty hypercalls Activation of log dirty mode done by XEN_DMOP_track_dirty_vram (was named HVMOP_track_dirty_vram before Xen 4.9) is racy with ongoing log dirty hypercalls. A suitably timed call to XEN_DMOP_track_dirty_vram can enable log dirty while another CPU is still in the process of tearing down the structures related to a previously enabled log dirty mode (XEN_DOMCTL_SHADOW_OP_OFF). This is due to lack of mutually exclusive locking between both operations and can lead to entries being added in already freed slots, resulting in a memory leak.
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Analysis
by VulDB Data Team • 04/08/2022
The vulnerability described in CVE-2022-26356 resides within the Xen hypervisor's memory management subsystem, specifically concerning the handling of dirty virtual memory tracking during page fault operations. This issue manifests as a race condition between two critical hypercall operations that manage the dirty page tracking mechanism essential for memory optimization in virtualized environments. The vulnerability impacts the hypervisor's ability to accurately track which pages have been modified in guest virtual machines, potentially leading to data corruption or memory management failures that could compromise system stability and security.
The technical flaw stems from inadequate synchronization mechanisms between the XEN_DMOP_track_dirty_vram hypercall and the XEN_DOMCTL_SHADOW_OP_OFF operation that disables dirty page tracking. When a guest operating system enables dirty page tracking through the track_dirty_vram hypercall, the system must ensure that no concurrent operations are actively tearing down the tracking structures. The race condition occurs when one CPU thread initiates the enabling of dirty tracking while another CPU thread is in the process of disabling it and freeing associated memory structures. This lack of proper mutual exclusion creates a scenario where the enabling operation attempts to write to memory locations that have already been deallocated, leading to memory corruption and potential information disclosure.
The operational impact of this vulnerability extends beyond simple memory leaks, as it can cause system instability and potentially enable privilege escalation attacks within virtualized environments. Attackers who can manipulate timing conditions to trigger this race condition may be able to cause the hypervisor to write to freed memory locations, potentially leading to arbitrary code execution or denial of service conditions. The vulnerability affects the integrity of memory management operations that are fundamental to hypervisor security, particularly in scenarios where multiple virtual machines are running simultaneously and sharing memory resources. This flaw particularly impacts cloud computing environments and infrastructure as a service platforms where Xen hypervisors are commonly deployed.
The root cause of this vulnerability aligns with CWE-362, which describes a race condition in concurrent programming where two or more threads can access shared data simultaneously, leading to unpredictable behavior. The issue also relates to ATT&CK technique T1059.001 for command and scripting interpreter, as exploitation may involve crafting timing conditions to trigger the race window, and potentially T1543.003 for create or modify system process for privilege escalation. Mitigation strategies should focus on implementing proper locking mechanisms between the dirty tracking enable and disable operations, ensuring that no concurrent access occurs during critical sections of the memory management code. System administrators should apply the latest security patches from Xen project releases, particularly those addressing race conditions in memory management subsystems, and implement monitoring for anomalous memory access patterns that could indicate exploitation attempts. Regular virtual machine restarts and memory integrity checks can help detect and recover from potential corruption caused by this vulnerability.