Overview
CVE-2025-40236 is a security vulnerability discovered and patched in the Linux kernel’s virtio-net subsystem. This flaw could potentially lead to an information leak when using GSO tunnels due to improper initialization of tunnel metadata. While the severity is not critical and has no CVSS score, understanding the issue and applying the fix is essential for maintaining a secure system.
Technical Details
The vulnerability stems from the virtio_net_hdr_tnl_from_skb() function. When a Generic Segmentation Offload (GSO) tunnel is negotiated, this function attempts to initialize tunnel metadata. However, it was found that the function failed to zero out unused receive hash (rxhash) fields within the metadata. This oversight could result in the transmission of potentially sensitive data from previous operations to the receiving end of the tunnel, leading to an information leak.
The fix ensures that these unused rxhash fields are explicitly zeroed, preventing the unintended exposure of potentially sensitive information.
CVSS Analysis
Currently, CVE-2025-40236 has not been assigned a CVSS score and severity rating by NVD or similar organizations. However, it is important to note that the absence of a CVSS score does not necessarily mean the vulnerability is inconsequential. The nature of an information leak, even if limited, warrants attention and mitigation.
Possible Impact
The impact of this vulnerability is primarily an information leak. Specifically, it could lead to the unintended disclosure of potentially sensitive data to a party operating at the other end of a virtio-net GSO tunnel. The specific nature of the information leaked would depend on the context of the virtualized environment and the previous network operations. While the risk is not classified as high, any potential data exposure represents a security concern and should be addressed.
Mitigation or Patch Steps
The recommended mitigation is to apply the patch associated with this CVE. This involves updating your Linux kernel to a version that includes the fix. Specifically, the following commits address the vulnerability:
The process for updating the kernel will vary depending on your Linux distribution. Consult your distribution’s documentation for instructions on how to apply kernel updates. In most cases, this involves using your distribution’s package manager (e.g., apt, yum, dnf) to install the latest kernel packages.
