CVE-2025-40051 in Linux
Summary
by MITRE • 10/28/2025
In the Linux kernel, the following vulnerability has been resolved:
vhost: vringh: Modify the return value check
The return value of copy_from_iter and copy_to_iter can't be negative, check whether the copied lengths are equal.
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Analysis
by VulDB Data Team • 05/20/2026
The vulnerability identified as CVE-2025-40051 resides within the Linux kernel's virtual host networking subsystem, specifically affecting the vringh component that handles virtio ring operations. This issue manifests in the improper handling of return value checks for memory copy operations that are fundamental to virtualized network communication. The vulnerability impacts systems utilizing vhost-net or similar virtualization frameworks where guest operating systems communicate with host networks through virtio interfaces. The flaw represents a subtle but significant deviation from expected behavior in how the kernel processes data movement operations between virtual and physical network interfaces.
The technical root cause stems from a flawed assumption in the vringh implementation regarding the return values of copy_from_iter and copy_to_iter functions. These functions are designed to copy data from or to kernel buffers and typically return the number of bytes successfully copied, which should always be a non-negative value. However, the vulnerable code incorrectly assumes that negative return values might occur, leading to potential misinterpretation of copy operation results. The actual problem emerges when the code fails to properly validate that the copied data lengths match expected values, creating a scenario where incomplete data transfers might go unnoticed. This type of error handling flaw falls under the category of improper handling of return values as classified by CWE-704, which specifically addresses incorrect handling of function return values that can lead to unexpected program behavior.
The operational impact of this vulnerability extends across virtualized environments where Linux systems serve as hypervisors managing multiple guest virtual machines. Attackers could potentially exploit this weakness to manipulate data flow between virtual machines and host networks, potentially leading to data corruption, information disclosure, or even privilege escalation within the virtualization layer. The vulnerability affects systems using vhost-net for network virtualization, which is prevalent in cloud computing environments, container orchestration platforms, and enterprise virtualization deployments. Since the issue occurs at the kernel level within the networking subsystem, the potential for widespread impact exists across various deployment scenarios where virtio networking is utilized.
Mitigation strategies for CVE-2025-40051 focus primarily on applying the upstream kernel patches that correct the return value checking logic in the vringh component. System administrators should prioritize updating their Linux kernel versions to include the fixed implementation that properly validates copied data lengths against expected values. The fix ensures that the code correctly handles the guaranteed non-negative return values from copy_from_iter and copy_to_iter functions by implementing proper length comparison checks rather than relying on negative value interpretations. Organizations should also consider implementing monitoring solutions that can detect anomalous network behavior patterns that might indicate exploitation attempts. Additionally, the vulnerability demonstrates the importance of rigorous input validation and return value checking in kernel space code, aligning with ATT&CK technique T1068 which focuses on exploiting vulnerabilities in kernel drivers and system components. Regular security audits of virtualization infrastructure and kernel modules should be conducted to identify similar issues that might exist in other subsystems, as the improper handling of system call return values represents a common attack surface in operating system security.