CVE-2025-38107: Azure Linux Attestation and Microsoft Artifact Risk

CVE-2025-38107 fixes a race in the Linux kernel’s ETS qdisc, and Microsoft’s public advisory names Azure Linux as a product that “includes this open‑source library and is therefore potentially affected” — but that wording is an inventory attestation for Azure Linux, not proof that no other Microsoft product can include the same vulnerable kernel code.

Background / Overview​

CVE-2025-38107 was assigned to a race condition in the kernel scheduling code (net/sched: ets), specifically a problematic interaction in ets_qdisc_change() that can be triggered when the SFQ perturb timer fires at an inopportune moment. The race can lead to incorrect qlen accounting and underflow of a parent qdisc’s queue length; upstream maintainers addressed it by changing the qdisc backlog handling to ensure packets are purged safely and locks are held correctly.
Multiple independent vulnerability trackers and distro advisories picked up the fix and catalogued affected kernels and fixed package snapshots. Amazon Linux’s advisory listing shows the CVSS context and fixed‑package mappings for several kernel channels; OSV likewise records the upstream summary and the stable branches that contain the corrective commits. These third‑party listings give operators the authoritative package-level signals they need to determine exposure for a given host or image.
Microsoft’s Security Response Center (MSRC) entry for this CVE uses a short product‑mapping sentence that has become common for Microsoft’s Linux CVE pages: “Azure Linux includes this open‑source library and is therefore potentially affected by this vulnerability.” Microsoft has also stated a programmatic commitment to publish machine‑readable CSAF/VEX attestations (a phasedn October 2025) and to update CVE product mappings if additional Microsoft products are identified as carriers of the implicated upstream code.

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What Microsoft’s one‑line attestation actually means​

Attestation, not exclusion​

When MSRC says a named product includes a component, it is performing a targeted inventory mapping for that pin terms:

• Microsoft inspected Azure Linux build artifacts and confirmed the upstream code referenced by the CVE is present in those Azure Linux images. That makes Azure Linux a known carrier and therefore an immediate remediation target.
• The statement is scoped to the named product; it does not assert that the same upstream code absolutely cannot appear in other Microsoft artifacts (WSL kernels, Azure MS node images, linux‑azure kernel builds, or other images and binaries). Absence of a public MSRC attestation for some other Microsoft product is absence of attestation, not proof of absence of the vulnerable component.

This pattern is deliberate: large vendors ship enormous numbers of artifacts, and a product‑level attestation is a pragmatic way to tell customers whatd confirmed. Microsoft’s public commitments also make it clear they intend to expand attestations over time and update CVE entries if more Microsoft products are found to contain the implicated code.

Why readers often misinterpret the phrasing​

Two cognitive shortcuts lead many operators to the wrong conclusion:

• “Includes X, therefore only X”: reading the MSRC line as an exclusivity statement. In reality, Microsoft is naming the product that it has verified — not saying it’s the only possible carrier.
• “If Microsoft doesn’t say it’s affected, it’s safe”: absence of a vendor attestation is commonly and dangerously treated as clearance. That is an operational mistake because many carriers of upstream code are build‑time choices and can exist in unexpected places.

Theosture is: treat the MSRC attestation as authoritative for the named product (Azure Linux); treat other Microsoft artifacts as unverified until they are attested or inspected.

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Is Azure Linux the only Microsoft product that could be affected?​

Short answer: No. Long answer: Azure Linux is the only Microsoft product Microsoft has publicly attested (so far) to include the upstream code tracked by CVE‑2025‑38107, which makes Azure Linux a confirmed remediation priority — but other Microsoft artifacts can and historically have included identical upstream kernel code depending on how those artifacts are built, packaged, or distributed.

Practical examples of other Microsoft artifacts that may carry the same kernel code​

• WSL2 kernel: Microsoft builds and ships a kernel binary for WSL2; if a WSL kernel build used a vulnerable kernel tree, Wrriers. Microsoft publishes WSL kernel sources and updates, so WSL kernels are an artifact class that requires verification.
• linux‑azure / Azure Marketplace images: Microsoft publishes kernel builds tuned for Azure and supplies curatetplace; those kernels are distinct artifacts that may or may not match the Azure Linux image inventory.
• AKS (node images) and managed node pools: node images or managed base images can use a Microsoft-provided kernel or a distro the provider of the kernel in the node image, the same upstream defect may appear.
• Container base images and SDK packages: binary artifacts that embed or carry kernel‑adjacent code or user‑space utilities that interact with kernel features can sometimes pull st particular kernel interfaces; the build pipeline matters.

In other words, any Microsoft artifact that ships a Linux kernel build or supplies an image containing the kernel can technically include the same upstream net/sched code that CVE‑2025‑38107 addresses. The attestation simply documents which productleted the inventory for and confirmed.

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Technical summary of CVE‑2025‑38107 (concise, verifiable)​

• Affected component: Linux kernel net/sched ETS qdisc, function ets_qdisc_change().
• Symptom: race condition leading to incorrect qlen accounting and possible underflow of a parent qdisc’s queue length; this can manifest as scheduler misbehavior or packet-drop anomalies under specific timing conditions.
• Upstream remedy: adjust backlog handling (use qdiscpurgequeue or equivalent safe purging) and fix lock/release ordering so the race cannot be exploited.
• Distribution/packaging status: multiple vendors and distribution trackers (OSV, ALAS, and several distro advisories) list fixed snapshots and package releases; operators should consult their distro advisory for the exact fixed package name and kernel package version.

These technical claims are corroborated by at least two independent sources (OSV and Amazon Linux advisory), which provide the stable‑tree commit mappings and fixed package references operators need to triage their fleets.

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What operator — prioritized checklist​

• Immediate: If you run Azure Linux images, treat them as in-scope and apply Microsoft’s updates or replace affected images as Microsoft directs. Microsoft’s attestation means Azure Linux images were inspected and found to include the implicated upstream code.
• Inventory: E‑supplied kernels and images in your estate (WSL2 kernels on endpoints, Marketplace VM images, AKS node pools, linux‑azure kernels, and company‑managed images that may have used Microsoft artifacts as a base). Don’t rely on absence of attestations as proof of safety.
• Verify: For each artifact, check kernel version/build and kernel config. Use commands such as:
• uname -a (to get kernel release)
• zcat /proc/config.gz or grep CONFIG_NET_SCHED /boot/config-* (to test whether net sched/qdisc features are enabled)
• review SBOMs and image manifests where available
  These checks reduce guesswork and show whether a given image actually compiled in ETS/STQ code paths.
• Patch and replace: Apply the distro or vendor kernel update that contains the upstream fix. If you cannot patch immediately, replace affected images with patched images or move workloads to unaffected images. Use rolling replacements and test in staging before mass deploy. (osv.dev
• Mitigations while you patch: If you depend on qdisc configurations that exercise ETS/SFQ features, consider avoiding those qdisc settings on exposed hosts until kernels are patched; isolate vulnerable nodes or reduce exposure to untrusted tenants. Monitor tc usage on build/orchestration hosts.
• Subscribe and automate: Ingest Microsoft’s CSAF/VEX attestation feeds (when available) and your distro advisories into your vulnerability management pipeline so future product mappings and fixes are automated. Microsoft has committed to publishing VEX/CSAF attestations and updating CVE entries if more products are found to be carriers.

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Detection and validation guidance​

• Kernel logs: watch for scheduler-related oops traces and qdisc errors in dmesg and the system journal; upstream advisory traces often contain the call stack patterns to match.
• Package-level checks: consult your distro’s security advisory for the exact package version that contains the backport or fix. For example, Amazon Linux and other distros list fixed kernel package identifiers in their advisories. Don’t infer fixed status from major kernel number alone; distros may backport fixes into older kernel version numbering.
• Image SBOM / manifest scanning: where available, use SBOMs produced at image build time to find the kernel build and configuration metadata. If a vendor provides a machine‑readable VEX/CSAF attestation for a product, ingest it and map it to your image catalog. Microsoft has begun this VEX rollout and will expand attestations over time.

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Why Microsoft started with Azure Linux — and why that matters​

Microsoft’s early CSAF/VEX coverage prioritized Azure Linux because the company maintains a discrete Azure Linux distribution and image family that it builds, publishes, and supports. That made Azure Linux an early candidate for a machine‑readable inventory mapping. By confirming Azure Linux as a carrier for a given upstream component, Microsoft provides Azure customers a high‑confidence, actionable remediation signal. However, this prioritization does not imply exclusivity: many other Microsoft artifacts are separate build‑time outputs that require their own inventory checks.

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Risk analysis: strengths and potential gaps in Microsoft’s approach​

Notable strengths​

• Transparency: Microsoft’s decision to publish CSAF/VEX attestations and make explicit product mappings improves automation and reduces manurs who consume those feeds. This is an operationally meaningful improvement over opaque advisories.
• Product-level clarity for Azure customers: by attesting Azure Linux, Microsoft gives Azure operators a clear immediate action item, enabling prioritization and fast remediation for cloud tenants.

Potential risks and gaps​

-es interim uncertainty: until Microsoft extends VEX/CSAF attestations to other product families, organizations that use a mix of Microsoft images must perform their own artifact discovery and cannot rely solely on MSRC pages. That leaves a window of manual work for defenders.

• Dynamic pages and scraping limits: MSRC content is presented via a JavaScript application; automated scraping may be unreliable for some consumers. Rely on the published machine‑readable CSAF/VEX feeds and your distro advisories as authoritative, machine‑ingestible sources.
• Shared build artifacts and d the same upstream code can appear in many places via rebuilds, vendor backports, or image reuse. This means a single attestation is necessary but not sufficient to prove global safety across a vendor’s entire portfolio.

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What to expect from vendors and what to demand from your supply chain​

• Expect vendors to expand VEX/CSAF coverage: Microsoft has publicly committed to expanding product mappings and updating CVE entries when additional Microsoft products are found to carry affected components. Track the VEX feeds and MSRC updates and automate ingestion.
• Demand SBOMs and attestations for images you consume: when you deploy Marketplace VM images, Manageor-provided containers, require SBOMs or attestations that document which kernel trees and packages were used to create the image. This reduces the manual verification burden.
• Maintain artifact-level verification in CI/CD: enforce image scanning, SBOM veriffig checks in your build pipelines so you do not unknowingly ship vulnerable binaries. This is how you scale security across tens‑of‑thousands of images.

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Final assessment and guidance​

Microsoft’s public advisory that “Azure Linux includes this open‑source library and is therefore potentially afe and actionable product‑scoped attestation: if you run Azure Linux images, treat them as confirmed carriers and remediate promptly.
However, Azure Linux is not the only Microsoft artifact that could technically contain the vulnerable net/sched ETS code fixed by CVE‑2025‑38107. Other Microsoft kernels and images (WSL2 kernels, linux‑azure builds, Marketplace images, AKS node images, and even some managed offerings) are build artifacts that require per‑artifact verification; absence of a Microsoft attestation for those artifacts is not evidence they are safe. Put plainly: Microsoft has attested what it has inspected; it has not (yet) attested everything.
Operationally, prioritize patching Azure Linux images, inventory and verify other Microsoft artifacts you rely on, ingest machine‑readable VEX/CSAF attestations as they arrive, and use distro advisories (OSV, ALAS, vendor advisories) to identify the exact fixed kernel package versions you must deploy. Treat the MSRC attestation as the high‑confidence signal it is — and use artifact‑level discovery to close the remaining blind spots.

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Conclusion: Azure Linux is the named, confirmed carrier in Microsoft’s public advisory for CVE‑2025‑38107, but it is not logically or practically the only Microsoft product that could include the implicated upstream kernel code. Microsoft’s attestation tells you where they have looked and what they confirmed; your job as an operator is to patch the attested product and to verify any other Microsoft artifacts you run until they are similarly attested or you can confirm they contain the upstream fix.

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Source: MSRC Security Update Guide - Microsoft Security Response Center