Understanding CVE-2025-38142: ASUS EC sensors bug in Azure Linux and Microsoft artifacts

A bug in the Linux kernel’s hardware-monitoring driver for ASUS embedded‑controller sensors — tracked as CVE‑2025‑38142 — was fixed upstream this summer, and Microsoft’s advisory for the issue explicitly attests that Azure Linux is a product that includes the affected open‑source component; however, that attestation is a product‑level statement of scope, not a technical proof that no other Microsoft artifact could contain the vulnerable code. This article explains what the bug is, which kernel trees and releases were affected and fixed, what Microsoft’s attestation actually means, and how administrators and developers should verify and mitigate exposure across Microsoft‑distributed Linux artifacts (Azure images, Marketplace images, WSL2 kernels, linux‑azure builds, and others).

Background / Overview​

CVE‑2025‑38142 is a medium‑severity Linux kernel vulnerability (CVSS ~5.5 in common assessments) in the hwmon subsystem’s asus‑ec‑sensors driver. The bug is a classic missing‑check / negative‑index issue: a helper function that looks up a sensor may return a negative error code (for example, -ENOENT) when a requested sensor is not present, and that negative value was not validated before being passed to a function that expects a non‑negative sensor index. The fix added an explicit check and returns a proper error code when the lookup fails, preventing a potential invalid memory access and the resulting kernel instability or crash.
The kernel community recorded the issue as introduced around the 5.18 merge and fixed in several stable branches with explicit backport commits. Upstream guidance is straightforward: update to a kernel that contains the upstream fix, or apply the individual stable‑branch fix if you cannot update the entire kernel tree.
Microsoft’s public advisory language says, in effect: “Azure Linux is the Microsoft product that we have verified includes the open‑source library and is therefore potentially affected.” That phrasing has been repeated across Microsoft VEX/CSAF attestations and MSRC advisory entries since Microsoft began publishing machine‑readable attestations for Azure Linux. It is an authoritative attestation that Azure Linux images should be treated as in‑scope for remediation — but it is not a technical guarantee that no other Microsoft product could ever contain the same vulnerable driver. Below I unpack why.

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CVE‑2025‑38142 — technical facts and patch status​

What the bug actually is​

• Component: Linux kernel hwmon drivers — file drivers/hwmon/asus‑ec‑sensors.c.
• Root cause: The function find_ec_sensor_index() may return a negative error code if the requested sensor is not found. The earlier code passed that return value straight into get_sensor_info() without a sanity check.
• Symptom: Passing a negative index into code that expects a non‑negative index may produce an invalid memory access, undefined behavior, or a kernel crash (DoS). The issue requires local access to trigger — it is not remotely exploitable by default.
• Typical attacker/prerequisite: An unprivileged local user (or process running on the host) calling the exposed hwmon sysfs or driver interfaces that enumerate or read sensor strings could trigger this condition by requesting a non‑existent sensor.

Where it was introduced and where it was fixed​

• Introduced around the 5.18 upstream merge.
• Fixed in multiple stable branches (example fixes landed in 6.1.142, 6.6.94, 6.12.34, 6.15.3 and in 6.16‑rc1 related commits). These fixes are the canonical upstream corrections; distribution vendors commonly adopt the stable patchsets into their kernels or ship fixed kernel packages.
• Upstream guidance: update to a kernel release that includes the fix, or apply the specific stable commit backport if you cannot upgrade the whole kernel.

Real‑world impact and exploitability​

• Scope: local, low‑privilege code can cause a crash or system instability. There is no credible public remote exploit vector tied to this driver in typical server configurations.
• Exploitation evidence: as of the upstream advisories and vendor reconciliations published around the disclosure window, there was no widespread proof‑of‑concept exploitation in the wild and the community EPSS values were low — this looks like a reliability / DoS class bug rather than an escalation/exfiltration vector.
• Severity: described as Medium by many vendors because it requires local access and affects availability (A in CIA), not confidentiality or integrity in the typical attack chain.

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Microsoft’s advisory: what “Azure Linux is the product” means — and what it does not​

Microsoft’s CVE mapping and the VEX/CSAF attestations began with a focused rollout that started with Azure Linux (the Microsoft‑maintained distro artifacts). When MSRC (or a Microsoft advisory) states that Azure Linux is the Microsoft product that includes the open‑source library and is therefore potentially affected, read it precisely:

• That statement is an attestation of inventory and verification for Azure Linux images at the time of publication. Microsoft has scanned and mapped the code in its Azure Linux artifacts and can declare with confidence whether those artifacts include the vulnerable upstream component.
• It is not a universal assertion that no other Microsoft product can or does include the same piece of upstream code. Microsoft’s VEX rollout was intentionally phased: they started with Azure Linux and are extending attestations to other product families over time. The wording explicitly promises updates to the CVE entry if additional Microsoft products are identified as impacted.

Put bluntly: absence of a Microsoft attestation for, say, WSL2 kernels or Marketplace images is absence of attestation, not proof of absence. Operationally that matters: many Microsoft products either ship or depend on Linux kernels (WSL2, azure VM kernel builds, marketplace images using vendor kernels, linux‑azure packaging used in some images, and so on), and whether they include this kernel driver depends on three technical variables:

• Which upstream kernel commit range or stable branch was used to build that artifact (was the driver introduced in that range?).
• Whether the kernel build configuration for that artifact enabled the ASUS EC sensors driver (kernel config symbol: CONFIG_SENSORS_ASUS_EC).
• Whether the artifact vendor or product applied additional patches or stripped drivers from their kernel tree before shipping.

Because of those variables, it is entirely plausible for other Microsoft‑distributed kernel artifacts to include the vulnerable driver. The conservative operational stance is to treat Azure Linux as the attested, confirmed hit, and to validate other Microsoft artifacts in your environment rather than assume they are unaffected.

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Why other Microsoft kernel artifacts could contain the driver​

The Linux kernel is built and packaged differently across artifact types. Consider these examples and how they affect inclusion of drivers:

• WSL2 kernel builds: Microsoft publishes the WSL2 kernel source tree and a canonical kernel configuration used to build kernels for Windows Subsystem for Linux. Historically, the WSL kernel configuration aims to keep the kernel small and exclude many platform‑specific drivers. In default WSL2 kernel configs seen in public WSL repos/configs, CONFIG_SENSORS_ASUS_EC has been not set in the WSL configuration snapshots we examined — which means the asus‑ec‑sensors driver is not built into those WSL kernels by default. However, WSL kernels are rebased over time and custom kernels are supported; a different kernel config (or a future upstream change) could include or enable the driver, so you should verify the kernel config for the WSL kernel version you run.
• Linux kernels backing Azure cloud images or marketplace images: Azure images may be built from an upstream kernel branch, or they may use distribution kernel packaging. If a kernel package includes CONFIG_SENSORS_ASUS_EC=y or =m and the build used an upstream range that included the buggy commit, that image would carry the vulnerable code until the vendor ships a fixed package.
• Custom or third‑party marketplace images: Many ISVs publish images that include kernels or kernel modules; these images are outside Microsoft’s immediate source tree and must be inventoried by customers.
• linux‑azure or Microsoft’s linux‑msft kernels: Microsoft maintains kernels and backports for certain Azure environments. Whether a given linux‑azure build includes the ASUS EC sensors driver depends on the linux‑azure kernel version and config used in the build.

Consequence: a one‑line vendor attestation that “Azure Linux is a product that includes the library” is meaningful and actionable for Azure Linux customers — but you cannot treat that single attestation as a global guarantee for all Microsoft Linux artifacts. You must do artifact‑level verification.

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How to check whether a given system (or Microsoft artifact) includes the vulnerable driver​

Use these practical, reproducible checks. Each step is short and intended for automation or quick triage.

• Determine kernel version and release string
• uname -r
• uname -a
• Inspect kernel config for the ASUS EC sensor symbol
• If /boot/config-$(uname -r) exists:
• grep -i 'SENSORS_ASUS_EC' /boot/config-$(uname -r)
• If /proc/config.gz exists:
• zgrep -i 'SENSORS_ASUS_EC' /proc/config.gz
• If you have a vendor config file (WSL or custom), inspect it for the same symbol: CONFIG_SENSORS_ASUS_EC=y or =m or commented out.
• Check for the driver module on the running system
• lsmod | grep -i asus
• modinfo asus-ec-sensors (or modinfo asus_ec_sensors) — if the module is present in the modules tree, modinfo will show it.
• Locate module file:
• find /lib/modules/$(uname -r) -type f -name 'asus' -print
• ls /lib/modules/$(uname -r)/kernel/drivers/hwmon/ | grep -i asus
• Check for device bindings or probes
• dmesg | grep -i 'asus' or dmesg | grep -i 'hwmon'
• ls /sys/bus/platform/drivers/ and look for entries that mention asus or asus_ec_sensors
• For WSL2:
• Check the WSL kernel release (inside WSL):
• uname -r
• If you rely on Microsoft’s distributed WSL kernel, verify the WSL kernel config in the published repo or the config file used to build your specific WSL kernel build.
• For WSL custom kernels, make sure the custom kernel build config does not enable CONFIG_SENSORS_ASUS_EC.
• For Azure VM images and Marketplace images:
• Query the kernel package version via aptitude/rpm/yum (dpkg -l linux-image-$(uname -r) or rpm -q kernel) and cross‑check whether that kernel release is earlier than the upstream fix. If the kernel version is inside the vulnerable range, look for distribution advisories or kernel updates that include CVE‑2025‑38142.

These checks let you answer two concrete questions for each artifact: (A) does the kernel build include the asus‑ec‑sensors driver?, and (B) is the kernel version in a range that predates the upstream fix? If the answers are yes/yes, treat the artifact as affected until patched.

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Mitigation and remediation strategy​

Follow these prioritized steps for operations teams and security owners.

• Immediately apply vendor patches if available
• For Azure Linux customers: follow Microsoft’s Azure Linux advisory and update the Azure Linux images or kernel packages Microsoft published. Microsoft’s attestation means Azure Linux images are in scope and should be patched as Microsoft directs.
• For other distributions (Debian, Ubuntu, Red Hat, SUSE, etc): install vendor kernel updates that include the stable patch backports for CVE‑2025‑38142. Most vendors publish security updates and fixlists that mention the CVE and the kernel package version you need.
• If you cannot update the kernel immediately
• Temporarily unload or blacklist the driver module (only if the module is built as a module and you confirm it is present). Example:
• modprobe -r asus-ec-sensors
• Create a blacklist file in /etc/modprobe.d/ to prevent the module from loading on reboot.
• Note: do not unload or blacklist the module if it is compiled into the kernel (CONFIG_SENSORS_ASUS_EC=y). Unloading only works for module builds and should be tested, as it can affect hardware monitoring functions for ASUS motherboards that rely on it.
• Harden local access to reduce attack surface
• Limit unprivileged access to systems where local users exist (container hosts, multi‑tenant machines).
• Monitor calls to hwmon sysfs nodes and unusual access patterns to sensor interfaces, if you maintain host‑level EDR or auditing for local syscalls.
• Inventory Microsoft artifacts in your estate
• Enumerate all Microsoft‑published Linux artifacts you run: Azure Marketplace images, AKS node images, WSL2 kernels on developer workstations, linux‑azure packages in your images, and any custom images derived from Microsoft artifacts.
• For each artifact, run the detection checklist above (kernel version + config + module presence).
• Treat Azure Linux as a confirmed affected product under Microsoft’s attestation; for other Microsoft artifacts, don’t assume they are not affected — verify.
• Use VEX/CSAF machine‑readable attestations as they become available
• Microsoft has explicitly moved to publish CSAF and VEX attestations beginning with Azure Linux. Use those machine‑readable artifacts to automatically map CVEs to Microsoft products where Microsoft has completed inventory and attestation. When Microsoft updates attestations for additional products, incorporate them into your automation.
• Track patch notes and the upstream stable commit references
• If you manage kernel build automation, consume the upstream stable commits that fix the driver rather than hand‑picking arbitrary code changes. Kernel maintainers recommend using the full stable release or the official stable patch backports rather than cherry‑picking unless you clearly understand the dependency context.

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Practical examples: commands and checks you can run now​

• Check kernel release:
• uname -r
• Search the kernel config for the driver symbol:
• grep -i 'SENSORS_ASUS_EC' /boot/config-$(uname -r) || zgrep -i 'SENSORS_ASUS_EC' /proc/config.gz
• Search for the module:
• find /lib/modules/$(uname -r) -type f -name 'asus' -print
• modinfo asus-ec-sensors || modinfo asus_ec_sensors
• Check whether module is loaded:
• lsmod | grep -i asus
• Check dmesg for driver probes:
• dmesg | grep -i 'asus' | tail -n 20
• For WSL2 specifically:
• In WSL: uname -r
• Compare the running WSL kernel release against the WSL2 kernel repo or your distribution’s notes; if you rely on the Microsoft‑provided WSL kernel, verify the Microsoft kernel config for CONFIG_SENSORS_ASUS_EC.

These commands are safe and non‑disruptive; they allow rapid triage.

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Risk analysis — strengths, limits, and operational pitfalls​

Strengths of Microsoft’s attestation approach​

• MSRC publishing of CSAF/VEX attestations improves clarity for Azure Linux customers — a confirmed attestation reduces guesswork and lets customers automate patching decisions for that product.
• The targeted attestation model allows Microsoft to provide high‑confidence statements about artifact inclusion without delaying remediation guidance for the attested product.

Limits and pitfalls​

• A published attestation for one product is not comprehensive for the whole Microsoft ecosystem. Customers who run varied Microsoft artifacts (WSL2 on developer machines, marketplace images, AKS, custom Azure VM images) must perform their own artifact-level verification.
• Some Microsoft kernel artifacts may be rebuilt or reconfigured over time. A driver disabled in one WSL kernel config snapshot may be enabled in a different branch or custom build. Static assumptions are unsafe.
• Relying solely on vendor attestation without confirming the build that runs in your environment is risky. Customers running upstream or third‑party images need to map binary provenance and build configuration.

Detection gaps and false negatives​

• If your kernel had the driver compiled in (not as a module), lsmod/modinfo will not show it and only inspecting the kernel config or the kernel image contents will reveal it. If /boot/config‑* is missing, you must extract the kernel config or rely on distribution packaging metadata.
• In cloud environments, images may be baked and deployed before vendor advisories; ensure image rotation and rebase procedures incorporate security scanning and patch automation.

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Actionable checklist for WindowsForum readers (summary)​

• Treat Microsoft’s Azure Linux attestation as authoritative for Azure Linux images; apply Microsoft‑published updates for that product without delay.
• Inventory every Microsoft‑distributed Linux artifact you operate (WSL2, Marketplace images, linux‑azure kernels, custom images derived from Microsoft artifacts).
• For each artifact:
• Check kernel version vs. upstream fix timelines.
• Check kernel config for CONFIG_SENSORS_ASUS_EC.
• Check for the presence of the asus‑ec‑sensors module and whether it is loaded.
• If the driver is present and the kernel predates the stable fixes, patch or update the kernel to a fixed version as your top priority.
• If immediate updating is impossible and the module is loadable/unloadable, consider unloading and blacklisting the module as a short‑term mitigation (test carefully).
• Monitor the MSRC VEX/CSAF feed for updates: Microsoft will expand attestations to additional products over time and update CVE records if more Microsoft artifacts are found to be affected.
• Add a kernel‑artifact verification step to your cloud‑image CI pipeline so future vendor attestations and upstream fixes can be mapped to your running artifacts automatically.

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Final assessment and takeaways​

CVE‑2025‑38142 is a straightforward upstream kernel bug with a low to medium operational impact in the majority of deployments: local access is required and the principal consequence is availability (kernel crash). The upstream fix is narrowly scoped and has been backported into stable kernel tree releases, and vendors have — or will — ship distribution updates that include those fixes.
Microsoft’s public statement that Azure Linux includes the affected open‑source library and is therefore potentially affected is meaningful: it is an authoritative attestation for Azure Linux customers and should be acted upon. That same statement does not prove other Microsoft products are unaffected; customers must verify other Microsoft artifacts running in their estates. Because many Microsoft products either ship kernels or publish kernel source and configs (WSL2, linux‑msft kernels, linux‑azure packaging, Azure Marketplace images), the safe operational stance is to verify artifact‑by‑artifact rather than rely on a single product attestation.
Security owners should use the concrete detection steps above to answer the binary questions that matter to risk and patching: does the kernel artifact you run include the asus‑ec‑sensors driver, and is the kernel version within the vulnerable range? If both answers are yes, patch or apply vendor kernels that include the stable backports immediately.
Finally, Microsoft’s VEX/CSAF rollout (started with Azure Linux) is progress: it reduces noise and gives customers a machine‑readable way to automate risk decisions for attested products. But transparency does not replace verification: for reliable protection, couple vendor attestations with artifact‑level checks and a processes to rotate and rebase kernels in cloud images as security fixes are published upstream.

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Source: MSRC Security Update Guide - Microsoft Security Response Center