Azure Linux Attestation and CVE-2025-38375: Implications for Microsoft Products

Azure Linux being named in Microsoft’s advisory is an important, actionable signal — but it is not a proof that no other Microsoft product contains the same vulnerable upstream code; Microsoft’s wording means Azure Linux is the only Microsoft product the company has completed and published an inventory attestation for so far.

Background / Overview​

CVE-2025-38375 is a Linux-kernel vulnerability that affects the virtio networking code: virtio-net: ensure the received length does not exceed allocated size. The bug lives in the virtio receive path (xdp_linearize_page and related receive code) and arises when received lengths are not validated against the actual allocated buffer size, which can permit an out‑of‑bounds read. The kernel community assigned CVE‑2025‑38375 and published upstream fixes; the typical remediation is to update to a kernel that includes the listed stable commits or to apply vendor backports. Microsoft’s public advisory described Azure Linux as the Microsoft product that “includes this open‑source library and is therefore potentially affected,” and the company simultaneously noted its rollout of machine‑readable CSAF/VEX attestations (starting with Azure Linux) and committed to updating the CVE/VEX mapping if additional Microsoft products are found to ship the same upstream component. That phrasing is deliberate: it is a product-level attestation for Azure Linux, not a blanket exclusion that other Microsoft artifacts cannot contain the code.

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What the vulnerability is (technical snapshot)​

• Affected component: virtio-net (networking driver code in the Linux kernel).
• Fault: missing or incorrect validation of the received length against the allocated buffer size during receive processing (xdp_linearize_page and the virtio receive path).
• Primary impact: out‑of‑bounds read, which leads to kernel instability or crashes (availability impact). Public trackers classify the practical threat model as local/host‑driven rather than instant remote code execution.

Upstream kernel announcements and multiple vendor trackers list the exact commits that fix the issue and identify the kernel branches to which the fix was merged. Operators should map their running kernel versions to the fixed commit IDs to confirm whether their kernels are vulnerable or already patched.

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What Microsoft actually said — precise reading of the language​

Microsoft has two connected statements you should read together:

• Microsoft published a VEX/CSAF attestation that maps the upstream component to Azure Linux and marks that product as potentially affected. This tells Azure Linux customers the company has validated that component inside that product’s builds.
• Microsoft also announced (October 2025) that it would publish machine‑readable VEX attestations and expand those attestations to other Microsoft products over time; Microsoft explicitly promised to update CVE/VEX records if additional Microsoft products are found to ship the same upstream code. That is a phased inventory process, not a global guarantee.

Put simply: Azure Linux is the only Microsoft product Microsoft has publicly attested (so far) as including the implicated library, but the statement does not technically prove that no other Microsoft product can or does include the same upstream code. The attestation is authoritative for Azure Linux; absence of attestation elsewhere is absence of published inventory, not proof of absence of the component.

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Are other Microsoft products plausibly affected?​

Short answer: Yes, they are plausible carriers — but Microsoft has not (yet) attested them as such.
Why this is true:

• Microsoft ships multiple Linux-derived artifacts or kernels that could, depending on version and build-time kernel configuration, include the same upstream virtio/driver code:
• Azure Linux (explicitly attested).
• CBL‑Mariner / linux-azure / Azure host images (used as container hosts or base OS images).
• Windows Subsystem for Linux (WSL2) kernel images — Microsoft maintains a WSL kernel tree and publishes prebuilt kernels; those kernels may include virtio drivers depending on configuration.
• Marketplace VM images or vendor kernels used on Azure — each image is a separate artifact and must be inventoried independently.
• A product contains the vulnerable code only if (a) its kernel version includes the affected commit range and (b) the kernel was built with the relevant configuration (virtio drivers compiled-in or as modules). Both factors are per-artifact build-time properties. Therefore the presence or absence of the vulnerability is an artifact-by-artifact question, not a universal company-level fact.

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Verified technical facts and cross-checks​

To ensure accuracy, the following key claims were verified against independent authoritative sources:

• The nature of the bug (missing received‑length check in virtio‑net / xdp_linearize_page) is documented in the Linux kernel’s CVE announcement and stable commit pointers. The kernel CVE mailing list entry clearly describes the problem and lists the stable commits that fix it.
• The CVE record and vendor advisories (SUSE, Red Hat trackers, Debian, Amazon Linux) reflect the same technical summary and map the fix into vendor packages and kernel backports. This confirms the upstream analysis and the practical remediation path (kernel updates/backports).
• Microsoft’s messaging about VEX/CSAF and the Azure Linux attestation was confirmed from Microsoft’s public VEX rollout blog and Microsoft’s CVE advisory language: Microsoft is deliberately rolling out machine‑readable attestations starting with Azure Linux and will update records if more products are discovered to ship the component. That is the procedural context for the Azure Linux statement.

Where the record is less certain or dynamic:

• Whether any particular Microsoft artifact beyond Azure Linux contains the vulnerable virtio code depends on inventories Microsoft may still be completing. Microsoft has pledged to update the VEX/CSAF data if and when it finds additional carriers. Until Microsoft updates those attestations, there is no public vendor attestation for other Microsoft products; that is a status-of-inventory fact, not a technical impossibility. This is a time-sensitive statement — check Microsoft’s VEX/CSAF feeds for updates.

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Practical guidance for administrators and engineers​

If you manage systems — whether running on Azure, on Windows (WSL2), or in on‑prem clouds — treat the situation with the following prioritized actions.

• Identify exposures (fast triage)
• List virtual machines and images that run kernels which may include virtio-net (Linux guests, Azure images, container hosts).
• For each artifact, run: uname -r to get kernel version and then map that kernel to the kernel stable trees that contain the fix (the Linux CVE announcement lists the fixed stable commits and fixed branch versions).
• Check for presence of virtio/net driver: grep -i virtio /lib/modules/$(uname -r)/modules.builtin modules.alias or inspect /boot/config-$(uname -r) for CONFIG_VIRTIO_NET. If virtio-net is built as a module, list modinfo virtio_net. These checks are lightweight and safe.
• Verify kernel patch level (how to confirm fix presence)
• Look up your distribution’s kernel changelog or package metadata to confirm whether it includes the upstream commit IDs referenced by the kernel CVE announcement. The kernel CVE post includes the exact commit IDs and the stable release points; use those IDs to match against distribution changelogs.
• Remediate
• Apply vendor-provided kernel updates that reference CVE-2025-38375 or the upstream commit IDs and reboot guests/hosts according to your change control policy. Distributors (Debian, Red Hat, SUSE, Amazon Linux) and kernel maintainers have published fixes and advisories — follow the vendor advisory for the specific package names and backports.
• Short-term mitigations if you cannot immediately patch
• Limit who can perform device hotplug or attach operations on your hosts.
• Harden vhost/vhost_net module usage and restrict management-plane APIs so tenants or untrusted users cannot modify host vhost behavior.
• Schedule a controlled maintenance window and test patches in staging before mass deployment. These are mitigations to reduce attack surface while you patch.
• WSL2 and Windows hosts
• If you use WSL2, check the WSL kernel image version that ships with Windows and whether that build contains virtio-net (WSL kernels are Microsoft-maintained); verify Microsoft’s VEX/CSAF or WSL kernel release notes, and update the WSL kernel if Microsoft publishes a fixed build. Because Microsoft publishes VEX data starting with Azure Linux and will expand coverage, if WSL2 is not listed in the VEX feed as affected that is an absence of attestation — you should still verify the WSL kernel build or contact Microsoft for clarification.

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How to interpret Microsoft’s VEX/CSAF approach (operationally)​

• Attestation-first rollout: Microsoft’s VEX rollout started with Azure Linux. The company is producing machine-readable attestations that answer “does product X ship component Y?” for each product family as inventory work completes. That makes each attestation a timely but partial inventory snapshot.
• Why this matters to customers: Azure Linux customers received an authoritative signal they can automate against (VEX/CSAF machine-readable files). Customers of other Microsoft products should not assume those artifacts are out of scope — they should query the VEX feed for their product or perform artifact inspection. The absence of a published attestation for a product does not imply immunity.
• Vendor transparency vs. completeness tradeoff: Publishing targeted attestations rapidly is a practical tradeoff: it gives customers immediate, actionable data for the most widely used product family while the vendor completes inventory for others. This is standard practice for large vendors with many product SKUs and binary artifacts.

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Strengths of Microsoft’s approach — why the Azure Linux attestation matters​

• Actionable machine-readable data: VEX/CSAF files allow automated triage systems to filter which CVEs apply to specific product artifacts rather than relying on noisy matching of library names. This reduces false positives and speeds remediation for Azure Linux customers.
• Clear vendor commitment: Microsoft explicitly committed to expand attestations and update CVE records if additional Microsoft products are found to ship the component. That procedural transparency is a useful improvement over opaque advisories.
• Alignment with upstream and distro trackers: The technical analysis (kernel commit IDs, fixed branches) matches upstream kernel announcements and the usual distro advisory flow; vendors and distros are rolling fixes and backports as expected. This makes remediation straightforward when vendor packages are available.

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Risks, caveats and remaining uncertainties​

• Inventory incompleteness is not the same as safety: Microsoft’s attestation for Azure Linux is authoritative for that product, but until Microsoft completes inventories for the broad set of Microsoft artifacts (WSL kernels, Marketplace images, container host builds, etc., other products may or may not include the vulnerable code. Treat missing attestations as unknown rather than safe.
• Time-sensitivity: The mapping of CVE → product artifacts can change as vendors backport fixes or discover additional carriers. Customers should monitor vendor VEX/CSAF feeds and distro advisories for updates.
• Complexity of kernel-based exposures: Whether a Microsoft product is affected depends on both kernel version and build configuration (what drivers/modules are enabled). This requires artifact‑level checks that many organizations must automate to avoid blind spots.
• No public exploit reported: As of the latest published advisories, this class of virtio receive-length bugs is seen primarily as an availability/stability risk (kernel oops / crash) with no credible public RCE exploit. Nevertheless, availability issues in multi-tenant cloud environments are operationally important and can be weaponized for denial-of-service. Treat claims of RCE cautiously and rely on vendor and upstream analysis for exploitability assessments.

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Recommended checklist for Azure and Microsoft‑hosted environments​

• For Azure Linux images:
• Immediately apply the Microsoft-published kernel updates or the Azure image updates that incorporate the upstream fix; follow Microsoft’s VEX/CSAF guidance for the attested images.
• For WSL2 and other Microsoft-shipped kernels:
• Check the WSL kernel version and Microsoft’s WSL release notes or VEX feed for any attestation or updates referencing CVE-2025-38375.
• If your WSL environment uses a custom kernel, ensure that custom kernel is patched or rebuilt with the upstream fixes.
• For hybrid fleets and multi-cloud:
• Inventory kernel versions and build configurations across images; check vendor advisories for your distribution and map those to the fixed commit IDs referenced in the kernel CVE announcement.
• For service providers and cloud operators:
• Harden vhost management-plane access and monitor for repeated guest crashes that might indicate abuse of a receive-length vector. Schedule coordinated kernel updates and reboots where necessary.

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Conclusion​

Microsoft’s advisory that “Azure Linux includes this open‑source library and is therefore potentially affected” is meaningful: it is an authoritative, machine‑readable attestation for Azure Linux that customers should act on. However, it is not a global statement that no other Microsoft product could include the same vulnerable virtio/driver code. Microsoft’s VEX/CSAF rollout deliberately started with Azure Linux and the company committed to updating CVE/VEX records if additional Microsoft products are found to ship the component. Until those attestations expand, operators should assume other Microsoft‑supplied Linux artifacts are potentially in scope and validate kernel versions and build configurations artifact-by-artifact.
Practical next steps are clear: inventory your kernels, map them to the upstream kernel commits listed in the Linux CVE announcement, and apply vendor or distribution kernel updates that reference CVE‑2025‑38375. Prioritize multi‑tenant and host components that use vhost/vhost_net, and monitor Microsoft’s VEX/CSAF feeds for attestations that expand beyond Azure Linux.

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Source: MSRC Security Update Guide - Microsoft Security Response Center