Microsoft has confirmed that its Azure Linux distribution is vulnerable to CVE-2025-38495, a buffer accounting flaw in the Linux kernel’s HID stack. But thanks to the phased rollout of Microsoft’s new vulnerability attestation system, customers who only patch Azure Linux may still have vulnerable Linux kernels running elsewhere in their environment.

The Vulnerability and Microsoft’s Response

CVE-2025-38495 is an upstream Linux kernel bug in the HID (Human Interface Device) core. A report-buffer accounting error—where code assumed an implicit report ID byte—could leave a buffer one byte too small, reducing an eight-byte guarantee to seven and causing out-of-bounds behavior in certain device report paths. Upstream maintainers committed fixes into the stable kernel trees, and numerous Linux distributions have already shipped patched kernels.

When Microsoft published its advisory for the flaw, it contained a specific and deliberately narrow statement: “Azure Linux includes this open‑source library and is therefore potentially affected.” The company also noted it began rolling out machine-readable CSAF/VEX (Common Security Advisory Framework / Vulnerability Exploitability eXchange) attestations in October 2025 as part of a transparency push. Crucially, the advisory adds: “If impact to additional products is identified, we will update the CVE to reflect this.”

That phrasing is accurate—but it’s a product-scoped attestation, not a declaration that Azure Linux is the only Microsoft artifact carrying the vulnerable code. It simply means Microsoft has so far inventoried and publicly attested only that one product family.

What CSAF/VEX Actually Means for This CVE

CSAF/VEX is a machine-readable format designed to help organizations automate vulnerability assessment. Instead of reading a prose advisory, a tool can ingest a VEX document that says, for a given product and CVE, whether it’s affected, not affected, or under investigation.

Microsoft’s rollout is phased. The company started with a bounded set of products it can inventory reliably—Azure Linux, which Microsoft builds, packages, and publishes directly—to provide high-quality attestations quickly. Other Microsoft-distributed Linux kernels, such as the WSL2 kernel, the linux-azure kernel used for certain VM SKUs, or the kernels inside Azure Kubernetes Service (AKS) node images, may also contain the same upstream code. But until Microsoft explicitly attests them in its VEX feed, their status is unknown.

As the advisory itself implies, the absence of a product name does not mean it’s safe. It means no attestation exists yet. This is the core message security teams need to understand.

Who Is Affected—and Who Might Be

Microsoft’s advisory puts Azure Linux customers in a clear position: they have an authoritative signal and should patch immediately following Microsoft’s remediation guidance. But the practical scope is wider.

Azure Linux Users

If you’re running Azure Linux images, you are the primary audience for this advisory. Microsoft’s VEX attestation for Azure Linux is the authoritative source; apply the updated kernel packages as soon as they’re available.

WSL2 Users

Windows Subsystem for Linux 2 ships with a Microsoft-built Linux kernel that is updated independently of Windows. The kernel version in your WSL2 environment may predate the upstream fix for CVE-2025-38495. Microsoft has not yet issued a VEX attestation for the WSL2 kernel, so it’s on you to verify. Run uname -r in your WSL2 terminal and compare the kernel version against the upstream fix commits. If in doubt, update WSL2 via Microsoft’s standard update mechanism or directly replace the kernel with a patched build.

AKS Node Images and Marketplace Offerings

Many Azure services use Linux kernels that Microsoft curates but does not necessarily manage as a single “product” for attestation purposes. AKS node images, for example, are updated on a cadence that may not align with this CVE’s advisory. Similarly, partner appliances or Linux images from the Azure Marketplace may run kernels in which the HID code is present. Without a VEX statement, you must check each artifact’s kernel version and configuration.

IT Administrators Across the Board

The takeaway is clear: if you run any Linux workload that originated from Microsoft—whether it’s a custom VM image, an AKS node, a WSL2 instance on employee desktops, or a container host—don’t assume it’s covered by the Azure Linux attestation. Inventory those artifacts, determine their kernel versions, and map them to the upstream fix for CVE-2025-38495.

How We Got Here

Microsoft’s move to CSAF/VEX is part of a broader industry shift toward automated, machine-readable vulnerability disclosure. For years, security teams have struggled to parse prose advisories and manually map vulnerabilities to their sprawling environments. VEX documents solve that by providing a deterministic signal that tools can consume directly.

Starting with Azure Linux was a logical, low-risk way to begin: Microsoft has complete control over that distro’s source, build, and delivery pipelines. It can say with confidence whether a given CVE applies. But Microsoft’s Linux footprint extends far beyond that single distro. The company ships multiple kernel artifacts for different purposes—from cloud-optimized VMs to desktop virtualization (WSL2)—and those kernels can diverge in version, configuration, and included drivers.

The upstream bug itself is a classic kernel robustness issue. It affects the HID core, meaning any kernel that enables HID support could carry the flaw—whether on a server, a laptop, or a virtual machine. The fix, once identified, was straightforward, and major distributions integrated it quickly. Microsoft’s acknowledgment, while limited in product scope, is consistent with its new transparency commitment. But it also highlights the reality that large vendors cannot instantly inventory every piece of open-source code they ship. The phased rollout is as much about operational pragmatism as it is about building trust.

What to Do Now

You can’t wait for Microsoft to expand its VEX feed. Here’s an actionable workflow for the next 48 hours.

  1. Identify every Microsoft-linked Linux artifact in your estate. This includes Azure virtual machines (note the exact image SKU and publisher), AKS node images, WSL2 instances on Windows machines, and any Marketplace or partner images you consume. Don’t forget development, test, and staging environments.

  2. For each artifact, get the kernel version. On a running host, uname -r gives the version string. For offline images, mount the image and inspect the kernel binary. Note the full version and, if available, the specific commit ID.

  3. Map the version to the upstream fix. The upstream commits that resolve CVE-2025-38495 are documented in the Linux kernel stable trees and referenced in advisories from Ubuntu, SUSE, and others. Cross-reference your kernel version with those commit IDs. If your kernel predates the fix, assume it’s vulnerable.

  4. Check kernel configuration. Even if the kernel version is old, the vulnerable code might not be compiled in. Inspect /boot/config-$(uname -r) or /proc/config.gz for HID-related options. If the HID subsystem is entirely disabled, you’re safe—but that’s rare in general-purpose kernels.

  5. Patch where you can, compensate where you can’t. For Azure Linux, follow Microsoft’s official update channel. For WSL2, update via wsl --update or manually replace the kernel. For AKS node images, check the release notes for updated images and plan node rotations. If a quick patch isn’t feasible, reduce exposure by restricting access to /dev/hidraw* devices, disabling USB passthrough where possible, and limiting untrusted user access to the host.

  6. Monitor Microsoft’s VEX feed. While you’re doing your own verification, keep an eye on Microsoft’s CSAF/VEX repository for new attestations. If additional products appear, you’ll need to act on those as well. Bookmark the MSRC update guide for this CVE; it’s the canonical location for changes.

Outlook

Microsoft’s phased CSAF/VEX rollout is a net positive for transparency, but CVE-2025-38495 exposes the gap between a vendor’s attestation ambitions and the messy reality of a mixed-source software supply chain. The company has committed to expanding attestations over time, but it hasn’t provided a timeline. For now, the burden of verification for anything beyond Azure Linux rests squarely on customers.

In the coming weeks, expect to see more distribution-level advisories confirming the fix, and possibly new VEX documents from Microsoft if it attests additional products. But don’t treat the absence of a VEX statement as a sign of safety. The lesson from this CVE is clear: when a vendor says “product X is affected,” that’s vital information—but it’s not the same as saying “only product X is affected.” Until the machines can read the whole story, humans still need to do the inventory.