CVE-2025-40056 in Linux
Summary
by MITRE • 10/28/2025
In the Linux kernel, the following vulnerability has been resolved:
vhost: vringh: Fix copy_to_iter return value check
The return value of copy_to_iter can't be negative, check whether the copied length is equal to the requested length instead of checking for negative values.
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Analysis
by VulDB Data Team • 05/20/2026
The vulnerability identified as CVE-2025-40056 resides within the Linux kernel's virtualization subsystem, specifically affecting the vhost framework and its vringh implementation. This flaw manifests in the handling of memory copy operations during virtual machine I/O processing, where the kernel incorrectly validates the return value of the copy_to_iter function. The vhost framework serves as a critical component for enabling efficient virtualization by providing userspace access to virtual device queues, making this vulnerability particularly significant for virtualized environments. The issue impacts systems utilizing virtio-based virtual devices that rely on the vringh subsystem for managing ring-based communication between virtual machines and host drivers.
The technical root cause of this vulnerability stems from improper validation logic within the kernel's memory copy handling routine. The copy_to_iter function is designed to copy data from kernel space to userspace iterators and should never return negative values under normal circumstances. However, the flawed implementation incorrectly checks for negative return values instead of verifying that the actual copied byte count matches the requested length. This fundamental error in conditional logic creates a potential path for unexpected behavior when memory copy operations complete successfully but fail the incorrect validation check. The vulnerability represents a classic example of improper error handling that could lead to denial of service conditions or potentially more severe consequences depending on the execution context.
The operational impact of CVE-2025-40056 extends across various virtualized environments where the Linux kernel's vhost framework is utilized, including cloud computing platforms, containerized deployments, and virtual machine orchestration systems. Systems running with virtio-based virtual devices that employ vringh for queue management are particularly vulnerable, as any attempt to copy data through these interfaces could trigger the flawed validation logic. The vulnerability may manifest as unexpected service interruptions, performance degradation, or complete denial of virtual device functionality, potentially affecting multiple virtual machines sharing the same host resources. Given that the vhost framework is integral to modern virtualization architectures, the potential scope of impact encompasses enterprise data centers, public cloud infrastructures, and any deployment utilizing Linux kernel virtualization features.
Security mitigations for this vulnerability involve applying the kernel patch that corrects the validation logic to properly compare the actual copied length against the requested length rather than checking for negative return values. System administrators should prioritize updating their kernel versions to include the fix, particularly in production environments running virtualized workloads. Monitoring for unusual system behavior or performance degradation in virtualized environments can help identify potential exploitation attempts. The vulnerability aligns with CWE-704 in the Common Weakness Enumeration catalog, which covers incorrect type conversion or comparison operations, and may be categorized under ATT&CK technique T1059 for execution through kernel-level modifications. Organizations should implement comprehensive patch management procedures to ensure all virtualization hosts receive the necessary updates, as this vulnerability could potentially be leveraged in broader attack scenarios targeting virtualized infrastructure components.