The Linux kernel team fixed a use‑after‑free in the IPC subsystem — tracked as CVE‑2025‑38212 — and Microsoft’s public CVE entry names Azure Linux as a product that “includes this open‑source library and is therefore potentially affected.” That statement is an authoritative, product‑level attestation for Azure Linux, but it is not a technical proof that no other Microsoft product or artifact can contain the same vulnerable kernel code. In short: treat Azure Linux as a confirmed, high‑priority carrier to patch now, and simultaneously verify other Microsoft‑supplied kernels and images (notably WSL2 kernels, Azure VM/marketplace kernels, and any Microsoft‑published kernel artifacts) because those are plausible carriers until proven otherwise. (msrc.microsoft.com)
CVE‑2025‑38212 is a kernel vulnerability described upstream as “ipc: fix to protect IPCS lookups using RCU.” The root cause is a race/lifetime problem: code paths that iterate an idr/radix structure in the IPC subsystem were not consistently executed within an RCU read‑critical section, which allowed a radix_tree_node to be freed (via call_rcu) and then immediately re‑read — a classic use‑after‑free. The practical symptom is kernel instability and potential local denial‑of‑service (kernel oops/panic); in the worst circumstances a skilled attacker in an appropriately privileged local context might elevate the impact. The vulnerability has been catalogued by NVD and picked up by major distributions and vendors; fixes were merged into stable kernel trees and rolled into distributor patches.
Why this matters operationally: this is a kernel‑level bug. Unlike a userland library that is invoked only by applications that include it, this kind of defect affects any kernel binary that includes the implicated source and whose build/configuration exposes the affected code paths. That means a given product is affected if and only if the kernel binary the product ships (or runs) was built from a source tree and configuration that contains the vulnerable code and has not received the upstream fix or an equivalent backport.
It is important to parse the sentence exactly:
Source: MSRC Security Update Guide - Microsoft Security Response Center
Background / Overview
CVE‑2025‑38212 is a kernel vulnerability described upstream as “ipc: fix to protect IPCS lookups using RCU.” The root cause is a race/lifetime problem: code paths that iterate an idr/radix structure in the IPC subsystem were not consistently executed within an RCU read‑critical section, which allowed a radix_tree_node to be freed (via call_rcu) and then immediately re‑read — a classic use‑after‑free. The practical symptom is kernel instability and potential local denial‑of‑service (kernel oops/panic); in the worst circumstances a skilled attacker in an appropriately privileged local context might elevate the impact. The vulnerability has been catalogued by NVD and picked up by major distributions and vendors; fixes were merged into stable kernel trees and rolled into distributor patches.Why this matters operationally: this is a kernel‑level bug. Unlike a userland library that is invoked only by applications that include it, this kind of defect affects any kernel binary that includes the implicated source and whose build/configuration exposes the affected code paths. That means a given product is affected if and only if the kernel binary the product ships (or runs) was built from a source tree and configuration that contains the vulnerable code and has not received the upstream fix or an equivalent backport.
What Microsoft actually said — and how to read it
Microsoft’s MSRC advisory language (the same phrasing you quoted) typically reads along the lines of: “Azure Linux includes this open‑source library and is therefore potentially affected by this vulnerability.” Microsoft also states that it began publishing machine‑readable CSAF/VEX attestations in October 2025 and VE pages if impact to additional Microsoft products is identified. That combination — a product attestation plus a promise to expand VEX mapping — is explicit and actionable for Azure Linux operators. (msrc.microsoft.com)It is important to parse the sentence exactly:
- “Azure Linux includes the open‑source library” is an inventory statement about a named Microsoft product family (the Azure Linux distribution). It confirms Microsoft looked at that product’s build outputs and found the implicated upstream artifact there.
- “Is therefore potentially affected by this vulnerability” signals that Microsoft treats that product as in‑scope for triage and remediation.
- The statement does not say “no other Microsoft product includes this component.” Absence of a product name from MSRC’s attestation is absence of attestation, not proof of absence.
Why Azure Linux was named first
Microsoft’s phased approach to publishing machine‑readable attestations (CSAF/VEX) started with Azure Linux because:- Azure Linux is Microsoft’s own Linux distribution and is therefore the most straightforward initial target for a high‑confidence inventory and SBOM/VEX generation.
- Publishing attestations for a single Microsoicrosoft provide deterministic, machine‑readable signals quickly while the company scales inventory and artifact mapping across many other SKUs and services.
- The MSRC statement and the October 2025 VEX rollout were explicitly designed to be incremental — Microsoft will update CVEs and VEX attestations as it completes inventories for other products.
Other Microsoft artifacts that can — and often do — ship Linux kernel code
Azure Linux being named does not imply Microsoft is the only place that kernel source appears inside the company’s artifacts. Microsoft builds and publishes several different Linux kernel binaries under different programs; any of these could include the vulnerable code depending on version and configuration:- Windows Subsystem for Linux (WSL2) kernel: Microsoft maintains the WSL2 kernel source and ships kernel binaries to Windows clients via Windows Update. The WSL2 kernel repo is public and receives regular releases; it is built from upstream kernel sources plus a set of Microsoft patches and configuration choices. Because Microsoft ships a real Linux kernel for WSL2, a WSL2 kernel that predates a backport of the CVE fix — or was built with the vulnerable code left enabled — could be affected. Verify the WSL kernel version on endpoints and apply WSL updates or custom rebuilds as needed. (github.com
- Azure VM images and Azure‑tuned kernels: Some Azure marketplace images and Azure VM SKUs run linux‑azure or Microsoft‑tuned kernel packages. These are distinct artifacts from the Azure Linux distribution but are functionally similar: they are compiled kernel partners ship into cloud images. Those kernel binaries must be inventoried and confirmed patched or backported. Community analyses and vendor advisories repeatedly emphasize that azure‑tuned kernels and marketplace images are plausible carriers.
- Marketplace and partner images, AKS node images: Marketplace appliances and partner VM images can ship kernels from many sour distro vendor ships a patched kernel, a partner image might repackage an older kernel or apply a custom build. Because the CVE is a kernel source issue, the specific kernel binary inside each image determines impact.
- Any Microsoft‑published kernel binary or image (for example, kernel builds for specialized appliances) that includes the implicated IPC code paths and has not received the fix is a candidate carrier. Microsoft’s attestation process will expand to more artifacts over time, but in the interim the onus is on operators to verify artifacts that matter to their environments.
How to determine exactly whether a Micr is affected — a practical checklist
The correct operational posture is simple: treat Azure Linux as “confirmed in‑scope” and immediately patch, and for all other Microsoft artifacts run the following artifact‑level checks.- Inventory: enumerate every place Microsoft‑published Linux kernels run in your estate.
- Azure VM images, custom Marketplace images, and AKS node pools.
- Developer and CI machines that use WSL2 (WSL kernel is updated independently).
- Any on‑prem or edge appliances built from Microsoft images or that include Microsoft kernel builds.
- For each Linux host or image, collect exact kernel metadata:
- uname -r to get the running kernel release.
- zcat /proc/config.gz or /boot/config-$(uname -r) to inspect the kernel configuration.
- Check installed kernel package versions and vendor advisories for the CVE mapping.
- For WSL2: inside WSL run uname -r to learn the kernel version; Microsoft’s WSL docs and GitHub repo provide release tags and change notes.
- Map the kernel version / package to upstream fixed commits:
- Use NVD, vendor advisories, and the kernel stable changelogs to learn which stabl contain the fix for CVE‑2025‑38212. Major distros and vendors (Ubuntu, Debian, Oracle, Red Hat, Amazon Linux) have listed fixed package releases. If your kernel is older than the fixed release and no vendor backport exists, assume vulnerability.
- Verify presence/absence of the vulnerable IPC path in the kernel binary:
- If you build kernels or ship custom images, inspect the source commit history or binary symbol mapping to check whether the vulnerable commit is present.
- For packaged kernels, rely on vendor advisories mapping CVE→package rather than raw version strings when possible.
- For WSL2 users and desktop fleets:
- Check Microtes and the WSL kernel binary version distributed via Windows Update. If your WSL kernel version predates the patched release, update WSL (or apply a custom patched kernel) and advise desktop users to update their systems. (github.com)
- Container images and static binaries:
- Remember: container images do not contain the host kernel. A vulnerable host kernel can affect containerized workloads even if the container image itself has no vulnerable kernel code. Conversely, statically linked userland binaries that embedded vulnerable userland lib remediate. Distinguish host/kernel remediation from image rebuilds.
- Document and automate:
- Ingest Microsoft’s CSAF/VEX feed once available and correlate VEX attestations to your asset inventory for automation. Microsoft’s VEX output for Azure Linux is immediately useful; subscribe for updates as Microsoft publishes more attestations.
Immediate remediation priorities and recommended timeline
- Immediate (hours): If you run Azure Linux images, apply the vendor remediation Microsoft has published for Azure Linux and reboot affected hosts as requiredion makes Azure Linux a canonical “known affected” product — act on it immediately.
- Near term (1–3 days): Inventory and verify WSL2 kernels across developer laptops and CI workers. Encourage/force Windows Update for clients where WSL kernel updates are delivered, or provide a patched custom WSL kernel forthe Windows Update rollout completes.
- Short term (3–7 days): Scan Azure VM images, AKS node pools, and Marketplace images used in production. For any image that contains an unpatched kernel, plan image replacement or kernel package upgrade and rolling reboot/orchestrated node replacemeneks): Integrate Microsoft’s CSAF/VEX feed into vulnerability management tooling so that when Microsoft expands attestations beyond Azure Linux, your systems will automatically update triage decisions. Also, require SBOMs or VEX attestations from third‑party image publishers where possible.
Technical and security analysis — strengths, gaps, and risk areas
Strengths- Microsoft’s decision to publish machine‑readable CSAF/VEX attestations is a measurable improvement in transparency. It reduces noise for Azure Linux customers and gives automated systems a deterministic signal for prioritization. That step should materially speed triage for Azure Linux and similar product families.
- Upstream kernel and major diickly: NVD and multiple vendor trackers list the CVE and mapped fixes into stable kernel trees and distribution packages, enabling straightforward remediation paths for most Linux consumers.
- Phased attestation rollout leaves a verification gap. Naming one product (Azure Linux) is the practical early step, but it creates an expectation that everything else is safe. That would be a dangerous assumption. Absence of a VEX attestation for WSL2, linux‑azure kernels, marketplace images, or other Microsoft artifacts is not a guarantee they lack the code — it simply means those artifacts have not yet been publicly attested.
- Multiple Microsoft‑shipped kernel artifacts. Microsoft publishdistinct kernel artifacts (WSL2 kernels, Azure‑tuned kernels, marketplace images), each with independent build and configuration decisions. Each artifact must be verified separately. The public attestation model must scale to cover these artifacts quickly to reduce residual uncertainty.
- Supply chain nuances: developers, build systems, partner images, and vendor packaging can replicate vulnerable code into places beyond a named distribution. For example, a vendor or developer might include the problematic IPC code in a custom kernel or an appliance image without immediate detection. This is why artifact‑level discovery (SBOMs, image scans, binary checks) matters.
- Userland mitigations do not fix kernel uilding userland components has no effect on a vulnerable kernel binary. Remediation for this CVE is primarily kernel updates/backports and reboots; any mitigation guidance that focuses solely on userland is insufficient.
- It is not possible from public data to exhaustively enumerate every Microsoft internal image, partner build, or ephemeral kernel used inside managed services. If a claim surfaces that “no Microsoft product other than Azure Linux ever contained this code,” treat it with skepticism until Microsoft publishes a VEX attestation or until you have local artifact verification. This is a fundamental supply‑chain transparency limitation that Microsoft’s own VEX program aims to reduce.
Practical commands and checks defenders can run now
- On a Linux VM or image (run as root or with appropriate reader access):
- uname -r
- zcat /proc/config.gz | grep -i 'CONFIG_'
- dpkg -l | grep linux-image (Debian/Ubuntu) or rpm -qa | grep kernel (RHEL/SUSE)
- Check vendor CVE advisories for kernel package mapping (use NV).
- On WSL2 (inside a WSL shell):
- uname -r # yields the WSL kernel release string
- If you rely on a custom kernel, rebuild with the upstream fix applied and update your .wslconfig to point to the patched kernel. Microsoft publishes the WSL kernel source and release notes which help map tags to changes.
- Image scanning:
- For Azure VM images: compare the image SKU and kernel package versions to distributor CVE advisories.
- For containers: scan base images for distribution kernel package lists (remember containers rely on host kernel). Use SBOMs and image scanners to flag binaries that embed kernel modules (rare) or vendors that ship kernels inside appliances.
Conclusion — concise operational answer
No: Azure Linux is not necessarily the only Microsoft product that can include the open‑source kernel code implicated by CVE‑2025‑38212. What is true and important: Azure Linux is the only Microsoft product Microsoft has publicly attested (via MSRC and its nclude the implicated code at the time of the advisory — and that makes Azure Linux a confirmed remediation priority. For every other Microsoft artifact (WSL2 kernels, Azure VM/marketplace kernels, AKS nodes, partner images), you must perform artifact‑level verification (kernel version, kernel config, package advisory mapping) to determine whether it is affected; absence of a Microsoft VEX attestation is not proof those artifacts are safe. Patch Azure Linux now, inventory your Microsoft‑supplied kernels and images, update WSL kernels where required, and integrate Microsoft’s VEX/CSAF feeds into your triage automation so you benefit from future attestations as Microsoft broadens coverage. (msrc.microsoft.com)Source: MSRC Security Update Guide - Microsoft Security Response Center
