CVE-2026-74520 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
iommu/iommufd: Fix IOPF group ownership UAF
iopf_group_alloc() links each last-page IOPF group into the generic IOPF pending list before invoking the domain fault handler. iommufd_fault_iopf_handler() also queued an accepted group in the IOMMUFD deliver list without removing it from the generic pending list.
When detach or HWPT replacement drops the device's IOPF reference count to zero, an IOMMU driver may call iopf_queue_remove_device(). That function responds to and frees groups through the generic pending list without removing the same groups from IOMMUFD's deliver list or response xarray. A later read, response, or cleanup can then access the freed group and cause a UAF.
Fix this by dequeuing an accepted group from the generic pending list before IOMMUFD queues it for userspace response. Make iopf_group_response() send a response regardless of pending-list membership, so the dequeued group can still be completed by IOMMUFD.
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability exists within the Linux kernel's IOMMU (Input-Output Memory Management Unit) subsystem, specifically in the iommufd component responsible for handling IOPF (IOMMU Page Fault) groups. The issue stems from improper synchronization between multiple internal data structures that manage pending and delivered fault groups during IOMMU operations. When an IOMMU driver processes device detachment or hardware page table replacement scenarios, it triggers cleanup functions that can lead to use-after-free conditions due to inadequate group list management.
The technical flaw manifests in the interaction between iopf_group_alloc() and iommufd_fault_iopf_handler() functions where groups are added to multiple lists without proper synchronization. When iopf_group_alloc() places last-page IOPF groups into the generic pending list, subsequent calls to iommufd_fault_iopf_handler() queue these same groups into the IOMMUFD deliver list while failing to remove them from the generic pending list. This dual-list membership creates a race condition scenario where cleanup operations can free memory that is still referenced in other data structures.
The operational impact of this vulnerability extends across virtualization and device management contexts where IOMMU functionality is critical for system security and stability. Attackers could potentially exploit this use-after-free condition to achieve arbitrary code execution within kernel space, particularly when malicious devices trigger fault conditions during cleanup operations. The vulnerability affects systems utilizing IOMMU with IOMMUFD subsystem, which are common in cloud environments, containerized deployments, and virtual machine configurations where device passthrough is implemented.
The fix implements proper list management by ensuring that accepted groups are dequeued from the generic pending list before being queued for userspace response in the IOMMUFD deliver list. This modification addresses the root cause by preventing the scenario where the same memory region could be freed while still referenced in multiple internal tracking structures. The iopf_group_response() function is enhanced to guarantee response delivery regardless of pending-list membership status, ensuring that all group processing paths can complete properly even after removal from the generic list.
This vulnerability aligns with CWE-415 which describes double free conditions and CWE-416 which covers use-after-free errors in memory management. The attack surface maps to ATT&CK technique T1059.003 for command and scripting interpreter, specifically shellcode execution within kernel contexts, and T1547.001 for privilege escalation through kernel exploits. The fix demonstrates proper resource management practices and follows established kernel security guidelines for concurrent data structure access patterns in IOMMU subsystem implementations.
The mitigation strategy requires updating to patched kernel versions that implement the corrected list management behavior. System administrators should prioritize deployment of these patches, particularly in virtualized environments where IOMMU functionality is actively used. Monitoring for anomalous system behavior or kernel oops messages during device detachment operations can help identify potential exploitation attempts. Additionally, implementing proper system hardening measures and maintaining up-to-date security configurations provides defense-in-depth against potential exploitation of this vulnerability class.
This issue represents a critical kernel-level memory corruption vulnerability that could enable privilege escalation attacks in environments utilizing IOMMU functionality with IOMMUFD subsystems. The vulnerability demonstrates the complexity of managing shared kernel resources across multiple subsystem interfaces and highlights the importance of proper synchronization mechanisms in concurrent kernel programming scenarios.