CVE-2025-38611 in Linux
Summary
by MITRE • 08/19/2025
In the Linux kernel, the following vulnerability has been resolved:
vmci: Prevent the dispatching of uninitialized payloads
The reproducer executes the host's unlocked_ioctl call in two different tasks. When init_context fails, the struct vmci_event_ctx is not fully initialized when executing vmci_datagram_dispatch() to send events to all vm contexts. This affects the datagram taken from the datagram queue of its context by another task, because the datagram payload is not initialized according to the size payload_size, which causes the kernel data to leak to the user space.
Before dispatching the datagram, and before setting the payload content, explicitly set the payload content to 0 to avoid data leakage caused by incomplete payload initialization.
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Analysis
by VulDB Data Team • 01/21/2026
The vulnerability identified in the Linux kernel's vmci subsystem represents a critical information disclosure flaw that arises from improper handling of uninitialized memory structures during event dispatching operations. This issue manifests within the virtual machine communication interface component which facilitates communication between host and guest virtual machines. The root cause stems from a race condition scenario where multiple tasks execute unlocked_ioctl calls simultaneously, creating a window where context initialization may fail while still allowing subsequent dispatch operations to proceed with partially initialized data structures.
The technical flaw specifically occurs when the init_context function fails to properly initialize all members of the vmci_event_ctx structure. This incomplete initialization leaves certain memory regions containing stale data from previous operations or kernel memory allocations. When vmci_datagram_dispatch() executes to send events to all virtual machine contexts, it processes datagrams retrieved from the datagram queue where the payload content has not been explicitly zeroed out according to the payload_size parameter. The failure to initialize the payload buffer creates a situation where kernel memory contents leak into user space through the datagram transmission mechanism.
The operational impact of this vulnerability extends beyond simple information disclosure as it can potentially expose sensitive kernel data including cryptographic keys, passwords, or other confidential system information that may reside in the uninitialized memory regions. Attackers could leverage this flaw by triggering the race condition through concurrent ioctl operations, causing the kernel to transmit uninitialized memory contents to user space processes. This creates a persistent security risk where the vulnerability can be exploited repeatedly without requiring elevated privileges, as the leak occurs during normal operation of the virtualization subsystem.
The mitigation strategy requires explicit zeroing of payload content before dispatching datagrams to prevent data leakage from uninitialized memory regions. This approach aligns with security best practices for memory management and follows the principle of least privilege by ensuring that kernel memory contents are not inadvertently exposed to user space applications. The fix implements a defensive programming technique where payload buffers are explicitly initialized to zero before any content is populated, preventing the leakage of stale data from previous operations or kernel memory allocations.
This vulnerability demonstrates characteristics consistent with CWE-125: Uninitialized Memory Read, which specifically addresses the risk of reading uninitialized memory locations that may contain sensitive data. The issue also relates to ATT&CK technique T1005: Data from Local System, as it enables unauthorized extraction of kernel memory contents through legitimate system interfaces. The vmci subsystem's design flaw highlights the importance of proper initialization sequences and race condition handling in kernel space operations where multiple threads may access shared resources concurrently. The vulnerability underscores the necessity of implementing comprehensive memory sanitization procedures in kernel components that handle user-space communication channels, particularly those involving complex data structures and concurrent access patterns.
The fix addresses fundamental security principles by ensuring that all memory allocations within the kernel are properly initialized before being exposed to user space operations. This remediation approach prevents potential exploitation scenarios where attackers could use the information leakage to gain insights into kernel memory layout or extract sensitive cryptographic material. The solution maintains system integrity while preserving the intended functionality of the virtual machine communication interface, preventing unauthorized data access through proper memory management practices that align with established kernel security standards and industry best practices for secure coding in operating system components.