Understanding CVE-2025-37830 The Linux SCMI cpufreq NULL Pointer Fix in Azure Linux

The recently assigned CVE‑2025‑37830 describes a NULL pointer dereference in the Linux kernel's SCMI cpufreq driver — a fix was merged upstream, and Microsoft’s MSRC entry explicitly notes that Azure Linux includes the affected open‑source code and is therefore potentially affected, while also promising to expand its machine‑readable VEX/CSAF attestations as inventory work continues.

Background / Overview​

The Linux kernel CVE team published CVE‑2025‑37830 to record a defect in the cpufreq System Control and Management Interface (SCMI) driver. The root cause is straightforward: the helper function cpufreq_cpu_get_raw() can return NULL when a requested CPU is not present in the policy->cpus mask, and scmi_cpufreq_get_rate() did not check that return value before dereferencing it — creating a classic NULL pointer dereference and a potential crash/denial‑of‑service for affected kernels. Upstream maintainers added a defensive NULL check and merged the change into the stable kernel trees.
This vulnerability is categorized as having a local attack vector and an availability impact: an unprivileged local actor (or a crafted workload running locally) could trigger the dereference, causing kernel instability or a crash. Public trackers list the issue as moderate in severity (CVSS v3.1 ~5.5 in vendor trackers) and show the usual vendor guidance: update kernels to versions that include the upstream fix or apply vendor backports where available.

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What the patch actually changed​

Technical snapshot​

• Affected file: drivers/cpufreq/scmi-cpufreq.c.
• Fault: missing NULL check after cpufreq_cpu_get_raw() in scmi_cpufreq_get_rate().
• Fix: add a defensive check for a NULL return and handle the error path, avoiding a dereference.

The kernel maintainers published the CVE announcement along with pointers to the specific commits that resolve the issue across supported stable branches. Those commits are the canonical source for the correct fix and are what distributors should backport into their kernel packages. The Linux kernel team explicitly recommends updating to a kernel release that includes the fixes rather than cherry‑picking individual commits unless you have a disciplined backport process.

Practical effect on running systems​

Because this is a NULL pointer dereference in a kernel driver, the realistic attacker outcome is a denial of service (system crash) or kernel panic. There is no indication in the public disclosures that this bug allows remote code execution, data corruption, or privilege escalation on its own — the impact is primarily availability. However, kernel panics can be weaponized in multi‑tenant cloud settings or used to disrupt critical services. Public trackers and vendor advisories recommend patching to maintain service reliability.

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Microsoft’s public wording — what it does and does not say​

Microsoft’s Security Response Center (MSRC) entry for CVE‑2025‑37830 includes this carefully worded FAQ text: “Is Azure Linux the only Microsoft product that includes this open‑source library and is therefore potentially affected by this vulnerability? … Azure Linux includes this open‑source library and is therefore potentially affected by this vulnerability. Microsoft is committed to transparency … we began publishing CSAF/VEX in October 2025. If impact to additional products is identified, we will update the CVE to reflect this.” (msrc.microsoft.com)
That language accomplishes two things simultaneously:

• It affirmatively attests that Azure Linux has been inventoried and found to include the vulnerable upstream component — in other words, Azure Linux is confirmed in scope for the CVE as Microsoft has mapped the upstream component into that product family. (msrc.microsoft.com)
• It does not assert exclusivity for other Microsoft artifacts. Microsoft explicitly ties this to its phased VEX/CSAF attestation rollout and promises to update mappings if additional Microsoft products are discovered to include the same component. The wording is therefore conservative and intentionally scoped to the product that has been verified, rather than claiming no other product could possibly carry the vulnerable code.

Put plain: Azure Linux = confirmed; other Microsoft products = unverified/under‑inventory until Microsoft updates its attestations or until each artifact is inspected.

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

Short answer: No — not necessarily. Azure Linux is the only Microsoft product Microsoft has publicly attested includes the implicated upstream component so far, but that attestation is a product‑level inventory statement, not a technical proof that other Microsoft‑distributed artifacts cannot contain the same kernel sources or compiled modules. Examples of other Microsoft Linux artifacts that could plausibly carry the same code include:

• WSL2 kernels distributed in Windows updates.
• linux‑azure kernels used in certain Marketplace images or Azure images.
• Kernel packages bundled into other Microsoft‑published images (Marketplace, AKS node images, managed appliances).
• Any custom images or maintenance artifacts Microsoft distributes where the kernel build picked up the upstream commit range that contained the vulnerable code.

Those artifacts must be inventoried on a per‑artifact basis. Microsoft’s public VEX/CSAF rollout is a mechanism to make those attestations machine‑readable, but the process is staged: Azure Linux was the initial product Microsoft validated and attested. Until Microsoft expands the attestations — or until individual customers inspect their deployed artifacts — it is operationally prudent to treat non‑attested Microsoft artifacts as unknown and therefore potentially at risk.

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How to determine whether your systems are affected​

Inventory is the only reliable starting point. For any Linux‑based workload (Azure VMs, on‑prem images, WSL hosts, container nodes, Marketplace images) you should determine:

• Which kernel version is running.
• Whether the kernel includes the SCMI cpufreq driver and whether that driver is built as a module or built‑in.
• Whether your kernel includes the upstream commit(s) that fix CVE‑2025‑37830, or whether the vendor has backported those fixes.

Actionable checks you can run immediately on a live Linux system:

• Check current kernel version:
• uname -r
• Look for the SCMI cpufreq driver in the kernel tree or loaded modules:
• lsmod | grep scmi_cpufreq
• grep -i scmi /boot/config-$(uname -r) || zgrep -i scmi /proc/config.gz
• ls /lib/modules/$(uname -r)/kernel/drivers/cpufreq/ | grep scmi
• If the driver is present as a module, list its path and check modification dates against vendor kernel packages:
• modinfo scmi_cpufreq
• Map your kernel version to upstream commits:
• Identify the kernel branch/series (e.g., 6.1.y, 6.5.y) then consult the stable kernel commit list referenced in the Linux kernel CVE announcement. The Linux kernel CVE post provides canonical commit URLs you can compare against your vendor package changelog or kernel source package.

If you find the driver present and your kernel version predates the stable commit that added the NULL check, the system should be considered vulnerable until patched or mitigated.

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Mitigation and patching guidance​

The single correct remediation is to run kernels that include the upstream fixes or to apply vendor backports distributed as kernel updates. The kernel team’s official guidance is to update to a stable kernel release that contains the fix; if that is not feasible, rely on your vendor’s security updates or well‑tested vendor backports. Do not attempt to surgically cherry‑pick kernel patches in production unless you have a rigorous kernel backport and testing pipeline.
Vendor guidance summary:

• Apply official kernel security updates from your Linux vendor (Azure Linux, Debian, Red Hat, SUSE, Canonical, Oracle Linux, etc.). Many distributors have already published advisories and package updates referencing CVE‑2025‑37830.
• For cloud or managed guests: apply the platform provider’s recommended security patch actions (for Azure VMs running Azure Linux, follow Microsoft’s Azure Linux updates and restart/reboot guidance as required). Microsoft’s MSRC attestation confirms Azure Linux is in scope and will be updated via VEX/CSAF as the company completes inventory for other artifacts. (msrc.microsoft.com)
• Where kernel updates are impractical: implement operational mitigations (isolation, limiting untrusted local access, restricting who can run workloads that might trigger the driver, and using kernel hardening features). Note these are stopgaps and do not remove the underlying vulnerability.

Recommended patching checklist for operators:

• Identify all systems running Linux kernels that could include SCMI cpufreq.
• Obtain vendor advisories or kernel changelogs and map them to the upstream commits listed by the kernel CVE announcement.
• Schedule and deploy kernel updates (test in staging first).
• Reboot or reload modules as required by your distribution’s update process.
• Validate post‑patch by verifying the kernel version or the presence of the upstream fix in kernel sources or package changelogs.

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Why the MSRC wording matters in practical patch operations​

Enterprise patching systems and vulnerability scanners typically correlate CVEs with a product inventory to produce action lists. Microsoft’s MSRC attestation that “Azure Linux includes this open‑source library and is therefore potentially affected” provides a machine‑actionable signal for customers who run Azure Linux images: patch those images immediately based on Microsoft’s advisory. (msrc.microsoft.com)
However, operational risk arises when teams assume exclusivity — i.e., they see MSRC naming Azure Linux and infer no other Microsoft artifact could be affected. That is a dangerous assumption. Across multiple CVEs in 2024–2025, Microsoft’s approach has been to start by publishing attestations for Azure Linux and then expand the VEX/CSAF coverage as internal artifact inventories are completed. In practice, defenders should:

• Treat Azure Linux as confirmed in scope and patch it per Microsoft guidance. (msrc.microsoft.com)
• Treat other Microsoft‑distributed artifacts (WSL kernels, linux‑azure builds, Marketplace images, AKS node images) as potentially in scope until Microsoft’s VEX files, additional advisories, or independent artifact inspection confirms otherwise.

This conservative posture aligns with the way upstream kernel components propagate: the same source files can appear in many different kernel builds and distributions depending on build time configuration, vendor backports, and kernel branch selection.

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Risk analysis: what operators should prioritize​

• Availability risk first: Because the vulnerability leads to kernel crashes, prioritize systems where availability matters: production VMs, database hosts, multi‑tenant hypervisors, and managed services. A denial of service in those contexts can have outsized consequences.
• Inventory and detection: The fastest risk reduction comes from accurate inventory and targeted patching. Use the commands listed earlier and your configuration management databases to identify all Linux artifacts and kernels in your estate. This is where Microsoft’s VEX/CSAF outputs become useful once they cover more products, because they can be machine‑ingested into automation.
• Cloud considerations: In cloud environments, kernels can be supplied by multiple parties — the guest OS vendor, the image author, or the cloud platform. Confirm whether your images use the distro kernel or a platform‑provided kernel (for example, some Azure images use linux‑azure variants). That determination changes who you rely on for updates and which advisories you follow.
• WSL & developer endpoints: WSL2 kernels distributed with Windows updates may also include upstream components; organizations that allow developer machines to run untrusted code should treat WSL hosts as part of the attack surface until attestations or artifact inspection proves otherwise.

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The limits of vendor attestations and the role of artifact inspection​

Microsoft’s VEX/CSAF rollout is a meaningful improvement in transparency: machine‑readable attestations let customers automate parts of triage and avoid false positives. But a VEX attestation is only as complete as the vendor’s inventory process. Because upstream code is reused across kernels and images, absence of a VEX mapping for a Microsoft product should be interpreted as “not yet attested” rather than “not affected.” Independent artifact inspection (checking the kernel image, modules, or package contents) remains the gold standard for validation.
Conservative defensive posture for operators:

• Patch Azure Linux immediately where it is used — Microsoft has attested that product. (msrc.microsoft.com)
• Inventory other Microsoft kernels/artifacts you run and validate whether they include the affected scmi code.
• Subscribe to Microsoft’s CSAF/VEX feeds and vendor advisories to pick up new attestations as Microsoft expands coverage.

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Practical checklist for administrators (quick reference)​

• Inventory: find all Linux systems and record kernel versions.
• Detect driver presence: run the module/config checks in the “How to determine” section above.
• Map kernel versions to upstream fixes: consult the Linux kernel CVE announcement for the commit IDs.
• Apply vendor patches and schedule reboots where required.
• For complex environments, prioritize patching by availability risk and exposure (multi‑tenant, managed services, critical infrastructure).
• Subscribe to VEX/CSAF feeds and vendor advisories to catch changes in product mappings.

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Notable strengths and unresolved risks​

The positive side of this event is threefold:

• The vulnerability was small and specific, and the upstream fix is simple and narrow — a defensive NULL check — minimizing the chance of regressions when vendors backport the change.
• The Linux kernel CVE process and vendor trackers reacted quickly and published the relevant commit links and advisories, giving vendors the material they need to produce safe backports.
• Microsoft’s VEX/CSAF rollout and the explicit attestation for Azure Linux give customers a machine‑readable signal to automate triage for that product family.

Remaining risks and gaps:

• The coverage gap: Azure Linux is the only Microsoft product explicitly attested so far, meaning other Microsoft artifacts remain unverified. If teams misread the MSRC wording as an exclusivity claim, they could miss other vulnerable images or kernels in their estates.
• Inventory inertia: Many organizations lack comprehensive, up‑to‑date inventories of kernel artifacts across clouds, developer endpoints, and managed services — making risk assessment slower than it should be.
• Operational friction: kernel updates and reboots are disruptive; organizations with strict uptime SLAs must balance patching speed against availability windows, which can lead to delayed remediation.

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Conclusion​

CVE‑2025‑37830 is a moderate‑severity Linux kernel null pointer dereference in the SCMI cpufreq driver that has an upstream fix. Microsoft’s public advisory explicitly attests that Azure Linux includes the affected code and is therefore potentially impacted, and Microsoft has committed to expanding its machine‑readable VEX/CSAF attestations as it inventories more products. That attestation is authoritative for Azure Linux, but it is not a proof that other Microsoft products cannot contain the same vulnerable code; those artifacts must be inventoried or attested separately.
Operators should patch confirmed‑in‑scope Azure Linux systems immediately, inventory other Microsoft kernels and images, check for the presence of the SCMI cpufreq driver, and apply vendor kernel updates or tested backports. Subscribing to MSRC’s CSAF/VEX feed and vendor security advisories will reduce manual work as attestations are added, but artifact‑level inspection remains essential to achieving full confidence that your fleet is clean.
Stay pragmatic: treat Azure Linux as confirmed affected and other Microsoft artifacts as unknown until verified — that approach minimizes operational risk while you complete inventory, testing, and patching.

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Source: MSRC Security Update Guide - Microsoft Security Response Center