CVE-2025-38160: Raspberry Pi Clock Driver NULL Pointer Fix and Azure Linux Attestation

The Linux kernel fix labeled CVE-2025-38160 patches a simple but meaningful null-pointer check omission in the Raspberry Pi clock driver: a call to devm_kasprintf() in raspberrypi_clk_register() could return NULL on allocation failure and the caller did not guard against that, allowing a kernel NULL-dereference and an availability-impacting crash. Microsoft’s public advisory for this CVE names Azure Linux as a product that “includes this open‑source library and is therefore potentially affected,” and that attestation is accurate for that product — but it is not, by itself, proof that no other Microsoft product can or does contain the vulnerable code. The practical answer for defenders is: Azure Linux is the only Microsoft product Microsoft has attested so far, but other Microsoft images and kernels may also be carriers until they are explicitly inventoried and attested.

Background / Overview​

CVE-2025-38160 is a classic kernel-level NULL pointer dereference rooted in a missing check after a memory-allocation helper. The upstream description is concise: devm_kasprintf() can return NULL when memory allocation fails, and raspberrypi_clk_register() used the result without verifying it. Upstream maintainers added a defensive NULL check to eliminate the dereference and the resulting kernel oops. The Linux CVE announcement and stable-tree commits identify the affected file as drivers/clk/bcm/clk-raspberrypi.c and map the fix to the stable kernel series listed in the upstream notices.
Why this matters operationally: kernel NULL dereferences typically produce an immediate kernel oops that can terminate the offending kernel task or, in the worst case, panic the whole system. The real-world impact is therefore availability loss — a local actor or misbehaving process able to exercise the driver could cause repeated crashes on an affected host. For Raspberry Pi devices and kernels that include the bcm rpi clock driver, the vulnerability is realistic and must be remediated by installing the upstream- or vendor-supplied kernel updates that include the backported fix.

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What the upstream fix actually changed​

Technical anatomy​

• Root cause: devm_kasprintf() returns NULL on allocation failure; the caller did not test the return value before dereferencing.
• Location: drivers/clk/bcm/clk-raspberrypi.c inside the Raspberry Pi-specific Broadcom clock driver.
• Fix: add a check for NULL immediately after devm_kasprintf() and avoid dereferencing or proceed with a safe error return if allocation failed.
• Affected kernel range and stable backports: the upstream CVE announcement and stable commit list show the change was introduced in an earlier commit and fixed in a range of stable releases; maintainers provided stable-tree cherry-picks to ease vendor backports.

This is a straightforward defensive change — small in code but important in production kernels where allocation can fail or where unusual early-boot ordering makes allocation failure transiently possible.

Why single-line fixes still matter​

Small, surgical memory-safety checks like this are common in kernel CVEs. They are easy to review and low-risk to apply, but they are also easy to miss in large upstream codebases. The critical operational point is that such defects are availability-focused: they do not, in themselves, commonly allow remote code execution, but they do make a host crashable by local actors or problematic device interactions. Distribution and vendor kernels need to pick up the patch and publish updated packages; until that happens, operators must treat affected hosts as vulnerable.

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Microsoft’s advisory: what it says and what it does not say​

Microsoft’s public messagl CVEs in 2025 has two distinct parts that are relevant here.

• For some CVEs Microsoft publishes a concise product-level statement asserting that Azure Linux includes the implicated open‑source library and is therefore potentially affected. That is a definitive inventory attestation for Azure Linux — Microsoft has inspected the artifact it calls “Azure Linux,” found the upstream component, and therefore declared the product potentially affected. This product-scoped attestation is machine‑readable when published via the CSAF/VEX files Microsoft began releasing as part of their transparency work.
• The company explicitly reserves the right to update the CVE mapping if additional Microsoft products are later found to ship the implicated library. In plain terms: Microsoft’s initial VEX/CSAF rollout started with Azure Linux as a tractable, high-priority inventory; other Microsoft artifacts are still being inventoried and will be attested later if they contain the component. Microsoft has communicated that this is a phased rollout: start with Azure Linux, then expand to other product families.

Important nuance: a VEX/CSAF attestation is an authoritative answer for the product it names. It is not an automatic exclusionary statement about every other product the vendor ships. Numerous technical, build-time, and process reasons mean that a given upstream source file may appear in some vendor artifacts and not in others — and those variations are precisely why vendors choose per-product attestations instead of a single, universal claim.
WindowsForum community analyses echo this point: Microsoft’s phrasing is deliberate and correct — Azure Linux is attested; absence of attestation for other Microsoft products is not proof of absence. In practice, defenders should treat “Azure Linux: affected” as confirmed and treat other Microsoft artifacts as unknown until Microsoft publishes additional attestations or until the customer inspects the artifacts directly.

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Is Azure Linux the only Microsoft product that includes the vulnerable library?​

Short answer: No — not necessarily. Longer answer and the reasoning follow.

Why Azure Linux may not be exclusive​

Microsoft distributes many separate Linux-related artifacts that are produced from different kernel sources, configuration sets, and packaging pipelines. Examples (non-exhaustive):

• The Azure Linux distribution (the one Microsoft attested) with its own kernel and package set.
• The linux-azure kernel packages that may be used in particular VM SKUs or referenced by marketplace images.
• Azure Marketplace base images and partner images, which may be built from different kernel sources or vendor-supplied kernels.
• **AKther managed-service images that are derived from base images and may carry patched or unpatched kernels depending on the build pipeline.
• WSL2 kernels that Microsoft ships inside Windows or provides as downloadable kernels for WSL images.
• Internal appliances, service-specific VM images, or partner appliances that Microsoft hosts or distributes.

Any of these artifacts could, in principle, include the same drivers and therefore be carriers of the vulnerable code if they are built from a kernel tree and configuration that included the affected drivers prior to the upstream fix. Because product-to-artifact mapping is complex and per-artifact, you cannot conclude exclusivity from a single product attestation. Community research and vendor advisories repeatedly emphasize that a product-level VEX statement is an authoritative “yes” for the named product and an informational “not yet attested” for the rest — which is operationally important for large environments that consume multiple Microsoft images.

When could other Microsoft products contain the code?​

• If a Microsoft image used a kernel commit prior to the upstream fix or backport, that image may carry the vulnerable file.
• If the bcm rpi clock driver was compiled into the kernel image (vs. built as a module) in a given artifact, that artifact is a potential carrier.
• If Microsoft or a partner rebuilt an image from an older kernel tree without applying the specific patch, those builds could be vulnerable even if Azure Linux is patched.
• Marketplace images created by third parties and published via Microsoft channels can carry third-party kernels; Microsoft’s attestation process may not have inspected every partner image at the time of their initial VEX rollout.

Because of those variables, the safe operational posture is to assume that non-attested Microsoft artifacts may be carriers until proven otherwise.

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Practical guidance for administrators anonsume Microsoft-provided Linux artifacts, these are the prioritized actions you should take now.​

1. Treat Azure Linux as confirmed in-scope (act immediately)​

• If you run Azure Linux images, apply the vendor-updated kernel or image that Microsoft lists as patched for CVE-2025-38160. The attestation means Microsoft has validated the component exists in those artifacts and will provide updates accordingly.

2. Inventory Microsoft-sourced images and kernels in your environment​

• Search your image and VM inventory for any artifacts that derive from Microsoft-provided images: VM marketplace images, AKS node images, WSL kernels, custom images created from Azure base images.
• For each image, collect:
• Kernel version and package name (uname -a, /proc/version, package manifest).
• Whether the bcm rpi clk driver is present as a module (look under /lib/modules/$(uname -r)/kernel/drivers/clk/bcm) or compiled into the kernel (check kernel config for the CONFIG_* flag during build).
• Any image SBOM or CSAF/VEX that Microsoft has published for that artifact (ingest those into your scanner). WindowsForum and Microsoft’s VEX rollout make this a practical approach.

3. Map kernel versions to the upstream fix​

• Upstream commit listings and the Linux CVE announcement map the fix to specific commits and stable backports. If your kernel versions are older than the fixed stable releases or were built from the earlier commit ranges, treat them as vulnerable until vendor packages indicate they have been patched.

4. Apply vendor patches or replace images​

• Prefer vendor-supplied kernel updates and patched images rather than cherry-picking single commits unless you run a validated custom build pipeline.
• For managed services (AKS, Azure VM scale sets), follow the provider’s guidance for image refresh and node pool upgrades. Microsoft has committed to updating CVE entries when additional products are identified, so stay subscribed to the vendor’s CSAF/VEX feed if you consume Microsoft artifacts.

5. Short-term mitigations (if immediate patching is impossible)​

• On systems where the driver is a module and the system does not require the driver, unloading or blacklisting the module reduces attack surface. Warning: on Raspberry Pi systems the driver may be required for basic hardware operation — blacklisting may be infeasible for those hosts.
• Constrain local-user access and untrusted workloads on hosts that carry the vulnerable driver. For multi-tenant or CI systems, remove device access to untrusted containers or sessions that could exercise kernel interfaces with the driver present.
• Increase monitoring for kernel oops / OOM / driver traces in dmesg and centralized logs; configure alerts for repeated OOPS patterns that may indicate attempted or accidental triggers.

6. Rebuild or revalidate third-party binaries/images​

• If you consume any marketplace or partner images that you cannot patch in place, consider rebuilding those images in your pipeline from a known-good kernel trwith vendor-patched images.

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How to verify whether other Microsoft products include the vulnerable file (concrete checks)​

• Extract or inspect the kernel package or kernel image used by the Microsoft artifact (for VM images, mount the image and inspect /lib/modules and /boot).
• Search the kernel tree or modules for the path drivers/clk/bcm/clk-raspberrypi.c or for the built module name. If present, correlate the kernel version and commit to the upstream commit ranges cited in the CVE announcement.
• If you cannot extract the kernel easily, collect runtime evidence from the live host: uname -r, lsmod, modinfo, and inspect the kernel config in /proc/config.gz (if present) for relevant CONFck the artifact against Microsoft’s published CSAF/VEX files; Microsoft’s VEX rollout is intended to make these attestations machine‑readable so you can automate matching. If an artifact is listed as “Not Affected” or “Known Affected,” use that as your authoritative signal; otherwise treat the artifact as “unknown” and validate manually.

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Critical analysis: strengths, limitations, and supply-chain risk​

Strengths of Microsoft’s approach​

• Product-scoped attestation is practical. Microsoft’s phased CSAF/VEX rollout gives customers a clear, machine-readable signal for at least one major product family (Azure Linux), reducing noisy false positives for that artifact. This heloritization for large cloud customers and security vendors.
• Transparency commitment. Microsoft’s public statement that it will expand attestations and update CVE mappings when additional products are found shows a commitment to improving inventory clarity across its supply chain.

Limitations and operational risks​

• Attestation != exhaustiveness. A VEX/CSAF attestation that names Azure Linux does not prove the component is absent from other Microsoft images or kernels. Defenders must therefore treat non‑attested artifacts as unverified rather than safe. This gap creates a verification burden for large enterprises that consume many Microsoft artifacts. Multiple WindowsForum analyses emphasize this caution and recommend per-artifact scanning.
• Marketplace and partner images. Third-party images published via Microsoft-managed channels may carry different kernels and are not necessarily included in Microsoft’s initial attestation scope. That can produce fragmented risk across an enterprise that uses both Microsoft- and partner-supplied images.
• Supply-chain drift. A patched base image can be re-used to create an unpatched derivative or a custom rebuild can reintroduce older kernel commits; without continuous artifact scanning, vulnerable components can reappear in downstream images. This is the fundamental supply‑chain risk that VEX/CSAF intends to mitigate but cannot eliminate without broad coverage.

Unverifiable claims and cautionary notes​

• It is currently unverifs single attestation whether any other Microsoft products contain the vulnerable file unless Microsoft publishes further attestations or your organization performs artifact-level inspection. Treat any exclusivity claim as unverified until the vendor attests more artifacts or your scans show otherwise. This is a subtle but important distinction that affects patch prioritization and image replacement strategies.

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Recommended policy for enterprise adoption of VEX/CSAF attestations​

• Integrate vendor CSAF/VEX feeds into your vulnerability ingestion pipeline and treat vendor attestations as authoritative per product.
• Maintain a per-image artifact inventory and a repeatable, automated scanner that inspects kernel modules, kernel config, and package manifests inside each image you consume.
• Prioritize remediation for products explicitly attested as “Known Affected” by vendors; for “unknown” artifacts, require either a vendor attestation or a local verification before downgrading remediation priority.
• Include a governance step in your image publishing process: any internal or partner image that uses vendor base images should be scanned and compared against the vendor’s published VEX/CSAF data before deployment. Microsoft has explicitly signalled that its VEX rollout will expand over time; use the VEX feed to automate re-checks as new attestations are published.

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Closing appraisal and concrete next steps​

CVE-2025-38160 is a straightforward kernel NULL-check omission in the Raspberry Pi clock driver that upstream maintainers fixed with a defensive guard. Microsoft has responsibly published an attestation that Azure Linux includes the implicated open-source library and is therefore potentially affected, and that attestation is an actionable signal for Azure Linux customers. However, the phrasing and the practical realities of kernel builds mean that Azure Linux is the only Microsoft product Microsoft has attested so far — it is not a definitive statement that no other Microsoft product can include the vulnerable code. Defenders must therefore combine vendor attestations with image-level inventory and scanning to achieve complete coverage.
Immediate checklist (one-page action plan)

• Confirm whether you run Azure Linux images; if yes, apply Microsoft’s patched Azure Linux image or kernel update now.
• Scan your entire fleet for kernels/images that include drivers/clk/bcm or the specific file drivers/clk/bcm/clk-raspberrypi.c. If present, map kernel versions to the upstream fix commits.
• For images you cannot patch quickly, apply short-term mitigations: unload/blacklist modules where safe, restrict untrusted local access, and increase OOPS monitoring.
• Ingest Microsoft’s CSAF/VEX attestations and schedule automated re-checks; treat vendor attestations as authoritative for the product they name, and treat non-attested artifacts as “unknown” until verified.

The practical takeaway for IT teams is straightforward: rely on Microsoft’s VEX/CSAF attestations where they exist (Azure Linux here), but do not let a single attestation lull you into assuming every Microsoft artifact is safe. Inventory, scan, and patch streams remain the operational foundation for reducing supply-chain and kernel-level risk.

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Source: MSRC Security Update Guide - Microsoft Security Response Center