CVE-2025-37930: Azure Linux Attestation and Nouveau Fix

The Linux kernel fix tracked as CVE-2025-37930 patches a race-condition robustness issue in the DRM/Nouveau fence handling code; Microsoft’s public advisory identifies Azure Linux as a product that includes the affected open‑source component and is therefore potentially affected, but that product‑level attestation does not prove Azure Linux is the only Microsoft product that could ever include the same vulnerable code.

Background / Overview​

CVE‑2025‑37930 was published in May 2025 and concerns a logic/race condition inside the Nouveau DRM driver used for NVIDIA GPUs in the Linux kernel. The underlying problem is a timing window in which a fence may be signaled by one code path while remaining listed in a pending list until removed by another updater; if a context‑teardown routine (nouveau_fence_context_kill()) runs during that window it may attempt to set an error on a fence that is already signaled, generating a WARN_ON and creating the potential for a kernel crash or memory‑robustness issue. Multiple upstream and downstream advisories classify the issue as medium severity with a CVSS v3 base score of 5.5 and describe it as an availability/robustness issue rather than an immediate information‑disclosure or remote code execution risk.
In response, kernel maintainers committed a targeted fix in the Nouveau driver to eliminate the race and the WARN_ON condition; downstream distributions and vendors have been mapping the upstream fix into their kernel package sets and publishing advisories indicating which artifacts are affected and which have been patched. Among major downstream trackers, Ubuntu, AWS/ALAS, and independent vulnerability databases have published summaries and affected-version ranges that mirror the upstream description.

Why Microsoft named Azure Linux — and what that wording actually means​

Microsoft’s Security Response Center (MSRC) entries for a set of Linux kernel CVEs (including CVE‑2025‑37930 and related driver fixes) frequently include the sentence: “Azure Linux includes this open‑source library and is therefore potentially affected.” That line is an authoritative, product‑scoped attestation: Microsoft has completed its inventory work for the Azure Linux family (the distro images it ships and maintains) and confirmed that those artifacts include the implicated upstream component. For customers running Azure Linux images, that statement is an actionable signal: treat the product as in‑scope and apply available kernel updates.
However, that sentence is also carefully narrow. Microsoft’s public attestation is a statement about the product artifacts the vendor inspected at the time of publication, not a universal guarantee that no other Microsoft product or artifact can or does include the same upstream source files. In plain terms: Azure Linux is the only Microsoft product Microsoft has publicly attested as including the affected Nouveau code in their CSAF/VEX output (at the moment the advisory was published), but other Microsoft‑supplied kernel images or distributions may also carry the same upstream code until explicitly inventoried and attested. The Windows and Linux communities have repeatedly emphasized this distinction because kernel sources are shared across many builds and build‑time configuration choices (CONFIG_* flags) determine whether a particular driver ends up in a shipped kernel binary.

The technical reason Microsoft’s attestation is scoped to Azure Linux​

There are two practical technical realities that make vendor attestations product‑scoped rather than universal:

• Kernel content is an artifact‑level property. The same upstream source tree can produce many different binary kernels depending on configuration flags (for example, whether Nouveau or other DRM drivers are built-in or as modules). A vendor must check each binary artifact to determine whether it actually includes the vulnerable code.
• Vendors often backport fixes. Distributions sometimes ship older nominal kernel version numbers while backporting specific upstream fixes. A binary could show as an older kernel release yet already include the upstream commit that removes the vulnerable window; conversely a newer release could remain vulnerable if the component was built differently. This makes per‑artifact verification necessary.

Because Microsoft’s initial CSAF/VEX rollout started with Azure Linux, the company’s earliest attestations were for that product family. Microsoft has stated it will expand VEX/CSAF attestations as its inventory work continues; until then, absence of a published attestation for another Microsoft product should be read as absence of attestation, not evidence of absence.

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Is Azure Linux the only Microsoft product that could include the vulnerable Nouveau code?​

Short answer: No — Azure Linux is the only Microsoft product Microsoft has publicly attested to include the implicated Nouveau driver for CVE‑2025‑37930 at the time of the advisory, but other Microsoft artifacts could also include the same upstream driver and therefore be in scope until verified or patched. Treat Microsoft’s attestation as authoritative for Azure Linux only.
Longer, technical answer:

• Microsoft publishes the source tree for its WSL2 kernel on GitHub, and that repository contains the drivers/gpu/drm area where Nouveau and other DRM drivers live. The presence of the driver sources in a Microsoft‑maintained repository demonstrates a plausible carriage path: Microsoft supplies kernel source and binary artifacts beyond Azure Linux (for example, the WSL2 kernel builds), and those artifacts may or may not enable the Nouveau driver at build time depending on kernel configuration. Verification requires per‑artifact inspection (looking for the driver files in /lib/modules, checking kernel config, or comparing kernel package changelogs). (github.com)
• Microsoft also ships other Linux kernel artifacts: linux‑azure kernel packages, kernels embedded in some Marketplace images and vendor appliances, and custom kernel builds used in specialized services. Any of these artifacts that include a kernel build enabling Nouveau could, in principle, be affected if they fall within the upstream commit ranges that the advisories mark as vulnerable. That is why security operators should not assume that non‑attested Microsoft products are automatically safe.
• Finally, configuration and patch posture matter more than an upstream version number alone. The vulnerable behavior is tied to particular commit ranges and behavior; downstream vendors may have already included the upstream fix in some artifacts while others still require patching. Cross‑checking vendor package changelogs, module presence, and kernel config flags is the only reliable way to establish exposure for any given Microsoft artifact.

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How defenders should respond — a practical runbook​

If you operate any Microsoft‑supplied Linux artifacts (Azure Linux images, WSL2 on developer machines, Azure Marketplace appliances, or linux‑azure package kernels), follow these steps to determine exposure and remediate the risk.

1. Inventory the artifacts that matter​

• List all Azure Linux images, custom images, and Marketplace appliances in active use.
• Enumerate endpoints where Microsoft‑supplied kernels are used: VMs, containers using host kernels, developer machines running WSL2, CI runners, and baked‑in appliances.

2. Check whether the Nouveau driver is present in the kernel image​

• On a running host, look for the Nouveau module or sources:
• lsmod | grep nouveau
• grep -i nouveau /boot/config-$(uname -r)
• ls /lib/modules/$(uname -r)/kernel/drivers/gpu/drm/nouveau
• If the driver is not present and not loadable, that artifact is not vulnerable to this Nouveau‑specific CVE. If it is present, continue to step 3.

3. Determine kernel version and patch status​

• Check uname -r and the vendor package version. Then compare to upstream advisories and distribution bulletins to determine whether the specific kernel includes the upstream fix or a vendor backport.
• Consult your distro/vendor security tracker (for example, Ubuntu Security Notices, Amazon ALAS, Red Hat, or Microsoft’s CSAF/VEX attestations) for whether the artifact is listed as patched or in need of update. Cross‑reference at least two independent trackers where possible.

4. Apply remediation where required​

• For Azure Linux images listed as affected by MSRC: apply the vendor kernel update (follow Microsoft’s published package updates for Azure Linux).
• For WSL2: update WSL from Windows Update or rebuild the WSL kernel from the microsoft/WSL2-Linux-Kernel repo with the patched upstream commit; if you run a custom WSL kernel, rebuild with the upstream fix applied. (github.com)
• For other Microsoft artifacts (Marketplace images, linux‑azure packages): follow the vendor’s remediation guidance or, if none is available, treat the artifact as potentially affected and patch or rebuild with a kernel that contains the upstream fix.

5. Mitigations and compensating controls​

• If immediate patching is not possible, limit access and privileges for affected hosts, ensure vigilant local logging for kernel oops/WARN_ON events, and avoid exposing those hosts to untrusted GPU workloads where local privileges could trigger the vulnerable code path.
• Consider disabling the Nouveau driver where practical (blacklisting the module) on systems that do not require NVIDIA Open‑Source driver functionality — but be cautious: blacklisting may impact GPU workloads or driver stacks that depend on Nouveau. Always test in staging.

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Detection: what to look for in logs and telemetry​

Because CVE‑2025‑37930 is an availability/robustness bug manifesting as WARN_ON or OOPS under race conditions, detection is primarily about monitoring kernel logs and crash telemetry:

• Look for kernel messages that include WARN_ON messages emitted by nouveau_fence_context_kill() or related nouveau fence debug strings; such messages often appear in dmesg, /var/log/kern.log, or equivalent telemetry systems.
• Correlate recent GPU workloads or driver module load/unload activity with kernel oops events.
• If you have centralized telemetry (SIEM or EDR with kernel event capture), write searches for nouveau-related WARN_ON or oops signatures and alert on those.

If you can reproduce the conditions in a lab, run targeted GPU workloads that exercise fence signaling and context teardown while monitoring kernel logs; reproducing the race locally can confirm both the issue and remediation efficacy after patching.

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Risk analysis — who should worry and why​

• Azure Linux customers who run kernel images Microsoft has attested are the primary audience for immediate action: follow MSRC guidance and apply Azure Linux kernel updates. Microsoft’s attestation is explicitly there to give those customers a clear, authoritative instruction.
• Other Microsoft artifact consumers (WSL2 users, Azure Marketplace image users, appliance operators) must not assume safety simply because they are not mentioned in an MSRC attestation. Those customers should inventory, verify driver presence, and patch if the driver was built into the kernel image. The WSL2 kernel source is available in Microsoft’s public repository, and that fact creates a plausible risk vector for WSL-based workloads if the driver is enabled in those builds. (github.com)
• The vulnerability’s exploitability profile favors local workloads that exercise the Nouveau driver and its fence handling code. This is not described as a remote, unauthenticated RCE — rather it is an availability/robustness weakness that can cause kernel WARN_ON or OOPS. Hosts that accept untrusted GPU workloads, host multi‑tenant containerized GPU workloads, or provide GPU passthrough/virtualization interfaces have higher operational risk exposure.

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Cross‑checking claims: why multiple independent sources matter​

To avoid false reassurance, I verified the core technical description and affected ranges against multiple independent trackers: upstream kernel notices and vendor advisories (Ubuntu and AWS/ALAS) reflect the same technical description of the race and WARN_ON, and independent vulnerability databases summarize the impact and remediation guidance. Microsoft’s MSRC entry provides the product‑attestation statement for Azure Linux and commits to expand CSAF/VEX attestations as inventory work proceeds; the WSL2 kernel repository demonstrates Microsoft ships kernel source that includes the drivers/gpu/drm tree. Taken together, these independent sources converge on the operational conclusions above: Azure Linux is the attested Microsoft product, but other Microsoft artifacts may contain the same code and must be verified per‑artifact.
If any of those claims cannot be independently verified for a specific artifact you operate, treat the artifact as potentially vulnerable until you can confirm the kernel lacks the Nouveau code path or includes the upstream fix.

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Strengths and limitations of Microsoft’s public attestation approach​

Strengths​

• Microsoft’s move to publish CSAF/VEX attestations provides actionable, machine‑readable signals for customers running Azure Linux. That lowers friction for automated vulnerability management in cloud images and helps customers prioritize patching for known affected artifacts.
• Publishing per‑product attestations allows Microsoft to provide precise remediation guidance for the product families they have audited. This is best practice for vendors with diverse product portfolios and multiple Linux artifacts.

Limitations and risks​

• The attestation is only as broad as the vendor’s completed inventory: customers who depend on other Microsoft artifacts (WSL2, Marketplace images, linux‑azure kernels) must not assume they are covered until the vendor explicitly attests them. This creates an interim period of uncertainty for organizations with mixed Microsoft‑supplied Linux artifacts.
• Product‑level attestations can lull teams into a false sense of completeness if they treat a single vendor statement as exhaustive across a company’s full artifact footprint. Operational defenders must still perform host‑level checks (lsmod, /lib/modules, kernel config, package changelogs) to validate exposure.

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Final recommendations (concise)​

• If you run Azure Linux: prioritize the kernel update Microsoft has published for the product family. Microsoft’s attestation covers these artifacts and is the authoritative signal for them.
• If you run WSL2, Marketplace images, linux‑azure kernels, or other Microsoft‑supplied kernel artifacts: inventory and verify. Check for the presence of the Nouveau driver in the kernel image and confirm whether the upstream fix is present or backported. If the driver is present and the artifact predates the fix, patch or rebuild. (github.com)
• If you cannot patch immediately: mitigate by reducing exposure to untrusted GPU workloads, increase log/telemetry monitoring for nouveau WARN_ON/OOPS symptoms, and consider temporarily disabling the Nouveau module where acceptable and safe.

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Conclusion​

Microsoft’s public statement that “Azure Linux includes this open‑source library and is therefore potentially affected” is deliberate and useful: it tells Azure Linux customers that their product images were inventoried and found to include the implicated Nouveau code and therefore deserve immediate attention. That attestation, however, is not an all‑clear for other Microsoft artifacts. Any Microsoft‑supplied kernel binary or image that includes the drivers/gpu/drm tree (or specifically builds the Nouveau driver) could — until verified otherwise — be within the scope of CVE‑2025‑37930. Defenders must therefore combine vendor attestations with per‑artifact verification (module presence, kernel config, package changelogs) and patch accordingly. The good news is that the upstream fix is narrow and has been widely propagated by distributions; the practical job for operators is to find which artifacts in their environment actually contain Nouveau, and then apply the available vendor updates or rebuild kernels to close the window.

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Source: MSRC Security Update Guide - Microsoft Security Response Center