CVE-2025-38136: Azure Linux Attestation and Microsoft Artifact Risk

The short answer: no — Azure Linux is not necessarily the only Microsoft product that could contain the vulnerable Renesas USBHS code, but it is the only Microsoft product Microsoft has publicly attested (so far) to include the specific upstream component that maps to CVE‑2025‑38136. Treat Microsoft’s public line as an authoritative, product‑level inventory attestation for Azure Linux, but not as proof that every other Microsoft image, kernel, or appliance is unaffected.

Background / Overview​

CVE‑2025‑38136 is a Linux kernel stability bug in the Renesas USB host controller driver (renesas_usbhs). The defect arises from an incorrect initialization order in usbhs_probe(): the code can access hardware registers before clocks and runtime power management are enabled, which on affected Renesas SoCs (notably RZ/V2H) can produce a synchronous external abort and an immediate kernel fault. The National Vulnerability Database and multiple downstream trackers record the same technical summary and the upstream commits that reorder clock and PM handling in probe.
The operational profile is straightforward and familiar to kernel engineers: this is an availability/stability issue (kernel oops / crash) caused by accessing device registers when clocks are not yet active. Public scorings place the CVSS v3 base score in the Medium range (typical vendor breakdown: AV:L/AC:L/PR:L/UI:N, A:High but C/I:None), because an attacker or script with local abilities to trigger probe/register access can reproduce the fault — but the vector is local rather than remote for default deployments.

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What Microsoft actually said — reading the MSRC attestation​

Microsoft’s CVE mapping pages follow a concise, repeatable template for many Linux kernel issues. For CVE‑2025‑38136 Microsoft’s publicly visible mapping includes the short inventory line you quoted: “Azure Linux includes this open‑source library and is therefore potentially affected by this vulnerability.” That language is an explicit statement that Microsoft inspected the Azure Linux product artifacts and found the implicated upstream kernel component inside those builds. It is an authoritative attestation for Azure Linux customers: if you run Azure Linux images, treat those images as in‑scope and apply Microsoft’s fixes or mitigations. (msrc.microsoft.com)
However, that MSRC sentence is product scoped — it affirms presence in the product Microsoft checked, not exclusivity across all Microsoft products, distributions, or images. Multiple independent analyses and vendor‑side advisories emiat a single product includes upstream code does not by itself exclude the possibility that other Microsoft artifacts (WSL kernels, linux-azure kernels, Marketplace images, container host kernels, AKS node images, OEM appliance images or partner VM images distributed through Microsoft channels) may also carry the same upstream files until those arted and attested.

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So — is Azure Linux the only Microsoft product potentially affected?​

Short, evidence‑backed answer:

• Azure Linux is the only Microsoft product Microsoft has publicly attested (so far) to include the specific vulnerable upstream component mapped to CVE‑2025‑38136. That attestation makes Azure Linux a confirmed remediation priority.
• But no — this attestation does not mean Azure Linux is the only Microsoft artifact that could include the renesas_usbhs code. Any Microsoft‑supplied artifact that ships a Linux kernel built from an upstream branch predating the upstream fix — and that enables the renesas_usbhs driver in the krule — could be a carrier until it is verified. Examples include WSL2 kernels Microsoft distributes, the linux-azure kernel used in some Azure VM images, Marketplace images or partner appliance images that bundle vendor kernels, AKS node images, and other customized kernels or images that Microsoft or its partners publish.

Why that matters: Microsoft’s attestation is an operational signal with immediate value — it tells you to patch Azure Linux. But it is not a certificate proving everything else is safe. Defenders who treat the sentence as an exclusive “only Azure Linux” statement risk leaving unverified Microsoft artifacts unexamined.

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Technical context: why the same upstream code can appear in many places​

The Linux kernel and many of its drivers are upstream, shared sources. Multiple downstream products can include the same upstream file(s) via:

• Stock distribution kernels that vendors package (Ubuntu, Debian, SUSE, RHEL family).
• Vendor‑maintained kernels for appliance and embedded devices (OEMs shipping boards with Renesas SoCs).
• Cloud provider custom kernels or kernel variants (for example, linux‑azure kernels tuned for cloud instance kernel artifacts: kernels used by WSL2, kernels embedded in Marketplace images, kernels in managed node images (AKS/VMs), or specialized images for appliances and developer tooling.
• Containers or images that include kernel modules or build artifacts (less common, but possible in specialized images).

Because renesas_usbhs targets embedded Renesas SoCs, the real exposure is concentrated in embedded fleets, SoC‑based appliances, evaluation boards and the small number of cloud VMs or images that are built to run on such hardware. On mainstream x86 server fleets the renesas driver is usually irrelevant — but the presence of the source in a kernel build, or of a module in /lib/modules for the running kernel, is the concrete signal you must check for each artifact you operate.

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How to verify whether an artifact you run includes the vulnerable driver​

Inventory is the practical center of gravity. Do not rely on product names alone — verify artifact contents.
Quick artifact‑level checks to run (examples):

• On a running host, check for the driver module or symbol:
• lsmod | grep -i renesas
• grep -i renesas /proc/modules
• modinfo renesas_usbhs (if module present)
• Inspect boot‑time kernel config for build‑time inclusion:
• zgrep CONFIG_USBHS /proc/config.gz or grep for renesas in /boot/config-$(uname -r)
• Search dmesg and journal for driver traces:
• dmesg | grep -i usbhs
• journalctl -k | grep -i renesas
• For imagehmands, rely on SBOMs / package manifests or request the VEX/CSAF attestations from the vendor that produced the image. If you publish or consume Marketplace images, inspect the image’s kernel package or ask the publisher for a verified SBOM.

If the module is not present and the target hardware is x86 servers without Renesas SoC footprint, exposure is unlikely. If the driver is present or the image is built for Renesas hardware, assume in‑scope until patched and verified.

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Mitigation and remediation: practical steps (priority order)​

• Prioritize Azure Linux images and nodes. Microsoft’s attestation means those images are confirmed carriers and should be patched or rebuilt with the fixed kernel as a priority. Apply the Microsoft‑published updates to affected Azure Linux images promptly.
• Patch kernels (the reliable fix). Install your vendor or distribution’s kernel update that contains the upstream fix (the upstream commits reorder clock acquisition and enable runtime PM early in usbhs_probe()). Verify package changelogs or kernel commit references to confirm the patch is present. Reboot into the patched kernel. Vendors and trackers (NVD, Amazon Linux advisories, distribution security advisories) list the upstream commit IDs and packages that include the fix.
• Short‑term controls if you cannot patch immediately:
• If ver is a module and you do not need the hardware functionality, unload it: sudo modprobe -r renesas_usbhs. Blacklist it across reboots via modprobe blacklist if acceptable. Test first — unloading kernel drivers can be disruptive on embedded devices.
• Restrict who can perform unbind/rebind or gadget operations: ensure unprivileged users cannot toggle driver bindings via sysfs.
• For hosted or virtualized environments, restrict USB passthrough and device redirection from untrusted guests so guest‑borne device input cannot induce host probe sequences.
• Verification and detection:
• After patching, reboot and confirm no oops traces in dmesg/journal referencing usbhs_probe or iowrite16 failures.
• Reproducen a lab (on a device representative of your fleet) to validate the bug no longer triggers.
• For fleets, stage the kernel update via canary/test → staged rollouts → full production, monitoring logs and crash metrics throughout.
• Coordinate with OEMs and partners:
• For embedded appliances, open a vendor support tickt confirmation that the vendor will backport the upstream commit into your device’s kernel tree and a timeframe for delivery. Many OEM kernels diverge from mainline and require vendor action to close the gap.

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Detection, monitoring and forensics​

• Monitor kernel logs (dmesg, journalctl -k) for oops traces that include usbhs_bset, usbhs_write, iowrite16, or stack traces mentioning renesas_usbhs. The NVD entry includes a canonical oops trace that is useful as a detection signature.
• Capture crash kernels (kdump), preserve serial console logs during reproduction, and gather full system journals when crashes occur — these are essential for forensic triage on embedded devices where access is limited.
• Add SIEM/EDR correlations that licrashes to recent device plug/unplug events or to processes invoking unbind/bind sequences. In some contexts (virtualization, USB passthrough), a guest may be able to trigger host probe behavior — monitor those subsystems closely.

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Why you should not be complacent if only Azure Linux is listed​

Microsoft’s statement that “Azure Linux includes this open‑source library and is therefore potentially affected” is an actionable, high‑value inventory signal: Azure Linux operators must act immediately. But the absence of the same MSRC attestation on other Microsoft product pages is not evidence of absence. Several independent reasons make broad verification necessary:

• Microsoft publishes CSAF/VEX attestations incrementally. Microsoft began publishing machine‑readable CSAF/VEX attestations in October 2025 and has committed to updating CVE mappings if additional Microsoft include a component. That process may lag discovery and publishing. Until attestations appear for other Microsoft artifacts, those artifacts should be treated as unknown and verified by artifact inspection. ([windowsforum.com](Azure Linux Attestation and CVE-2025-38257: What It Means for Microsoft Artifacts code means the same source file can appear in many kernels: upstream commits flow into multiple downstream kernel trees and vendor backports can vary in timing. A kernel built and packaged by Microsoft for WSL2 or a Marketplace VM image could cherry‑pick or includto the fix unless explicitly updated.
• OEM and partner images may ship vendor kernels with different maintenance cadences. Embedded fleets and appliances are the classic place where upstream security fixes take longest to arrive. Until the vendor confirms a backport, the device is effectively unpatched.

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Recommended practical program for defenders running Microsoft artifacts​

• Immediate triage (first 24–72 hours)
• Patch all Azure Linux images and nodes using Microsoft’s updates.
• Identify and quarantine any devices or images known to run on Renesas SoCs or that include renesas_usbhs.
• If you can’t patch immediately, apply short‑term mitigations (module unload, device lockdown).
• Short‑term sweep (1 week)
• Run artifact‑level discovery across your Microsoft‑supplied images and binaries: check WSL2 kernel versions, linux-azure kes, AKS node images, Marketplace images and any partner appliance images you operate.
• Use SBOMs, package manifests, and image scans to search for renesas_usbhs or related kernel object files. If a publisher supplies a CSAF/VEX attestation, ingest it to short‑circuit your checks.
• Medium term (1–3 months)
• Build a recurring image verification program: require SBOMs and VEX attestations from image publishers, and integrate artifact scanning into CI/CD for custom images.
• Establish a kernel patch policy for embedded fleets: require vendor confirmation of backports or vendor images rebuilt with upstream fixes.
• Long term (programmatic)
• Treat the upstream kernel as a first‑class dependency: capture and track upstream commit shipments into your images and require traceability for kernel patches.
• Automate cross‑product attestation intake (CSAF/VEX) into your vulnerability management pipeline so product‑level attestations are machine‑actionable.

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Critical analysis: strengths and remaining risks​

Strengths of the upstream fix and vendor response

• The technical fix is surgical: enabling runtime PM and acquiring clocks earlier in usbhs_probe removes the root cause without complex rearchitecting. That makes backporting simpler and reduces regression risk. Upstream commits and stable release backports are available and have been recordtion trackers.
• Microsoft’s public attestation for Azure Linux is useful: it gives Azure Linux customers a clear, authoritative remediation target and aligns Microsoft’s disclosure posture with machine‑readable VEX/CSAF rollouts.

Limitations and operational testation process is incremental. Until Microsoft publishes VEX attestations for all products, defenders must not infer universal coverage from a single product mapping. Vders often operate dozens of images and artifacts; a single attestation does not sweep that surface.

• Embedded and OEM kernels remain a practical weak spot. Devices shipped with vendor kernels can lag in receivin fixes, and that window can be long.
• Livepatch coverage may not include this kind of structural probe ordering fix for all providers; do not assume livepatch removes the need for a reboot into a patched kernel without explicit vendor confirmation.

Unverifiable claims and where to be cautious

• If you do not have artifact access to certain Microsoft images (for example, sealed appliance images or closed partner images distributed through Microsoft channels), you cannot assume those images are unaffected simply because the MSRC page currently lists only Azure Linu must demand SBOMs or formal attestations from the image publisher. This practical requirement is an inference from how upstream code propagates; the assertion that any given image includes the code needs artifact confirmation.

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Bottom line — what to do now​

• If you run Azure Linux: patch immediately. Microsoft’s attestation makes these images a confirmed remediation priority.
• If you run other Microsoft kernels or images (WSL2 kernels, linux‑azure, Marketplace, AKS node images, partner appliances): do not assume you are safe. Run artifact‑level checks (lsmod/modinfo, kernel config inspection, SBOM/image scans). If you cannot inspect an image, request a VEX/CSAF attestation or vendor confirmation.
• If you operate embedded or OEM devices using Renesas Sour OEMs and require backport confirmation; apply mitigations where feasible (module unload, device lockdown) until the vendor supplies a patched kernel.

CVE‑2025‑38136 is, technically, a narrow and fixable kernel stabilization issue — but fixing the code upstream is only part of the operational job. The industrial reality of Linux kernel use means the same upstream driver can be present in many artifacts; Microsoft’s Azure Linux attestation is a valuable and actionable signal, but not a universal proof of safety across all Microsoft products. Prioritize patching Azure Linux, then run a measured, artifact‑level verification program across all Microsoft‑supplied kernels and images you operate until formal attestations or SBOMs demonstrate those artifacts are clean.

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Source: MSRC Security Update Guide - Microsoft Security Response Center