Azure Linux and CVE-2025-38222: Ext4 Bug Not Exclusive to Microsoft

Microsoft’s short product attestation that “Azure Linux includes this open‑source library and is therefore potentially affected” is useful — but it is a product‑scoped inventory statement, not proof that no other Microsoft product or image can include the same vulnerable ext4 code. rview
CVE‑2025‑38222 is a kernel‑level correctness bug in the ext4 filesystem’s inline‑data path. The root cause is a length‑type mismatch: ext4_prepare_inline_data used an unsigned int for a length parameter where a wider loff_t was required, allowing a high offset/length to truncate and subsequently trigger a kernel BUG or panic when write_end verifies pos + len against inode inline size. Upstream trackers and multiple distributors document the same call trace, reproduce steps, and the change to use a loff_t as the corrective action.
This is primarily a local kernel stability/availability issue rather than a simple, remote exploit; the canonical repro shows a user process performing a pwrite at an extremely large offset that triggers truncated arithmetic and a BUG_ON in ext4_write_inline_data. Distributors and security trackers classify the issue as medium severity for typical environments (local vector, availability impact), and they mapped fixes into their kernel packages shortly after upstream merges.
Microsoft’s public advisory text for some Linux CVEs uses a short FAQ line that names Azure Linux as a confirmed carrier of an affected open‑source component and promises to publish machine‑readable CSAF/VEX attestations, while committing to update mappings if additional Microsoft products are identified. That wording has been repMSRC entries and is the basis for the current question.

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What Microsoft’s wording actually communicates​

Product‑scoped attestation, not exclusivity​

When Microsoft says “Azure Linux includes this open‑source library and is therefore potentially affected,” they are communicating the result of a product‑level inventory: Microsoft inspected the Azure Linux images/build outputs, found the implicated upstream component, and therefore marked Azure Linux as in‑scope for remediation. That statement is authoritative for Azure Linux as a product familyr customers who run those images.
Importantly, that same statement does not assert that Azure Linux is the only Microsoft artifact to ever include the code. The absence of a Microsoft attestation for other products is an absence of mapping or attestation — not a technical guarantee those other artifacts are clean. Multiple community analyses and vendor guidance make this point repeatedly: vendor attestations are phased, and large vendors typically begin with the product families they have the most complete inventories for.

Why vendors publish product‑scoped attestations first​

• Large vendors ship hundreds or thousands of distinct images and compiled artifacts. Exhaustively scanning and publishing attestations for every single artifact is operationally heavy; vendors commonly publish attestations for particular product families as inventories complete.
• A product attestation gives a machine‑readable signal (CSAF/VEX) that customers can feed into automated triage and patch orchestration for that product family.
• The attestation approach reduces the triage window for confirmed carriers (here, Azure Linux) while the vendor continues inventory work for other artifacts.

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Short answer to the user’s question​

No — Azure Linux is not necessarily the only Microsoft product that can include the vulnerable ext4 code tracked by CVE‑2025‑38222. Microsoft has publicly attested that Azure Linux includes the component and is potentially affected (making Azure Linux a confirmed carrier), but that attestation is product‑scoped; other Microsoft‑supplied artifacts (WSL2 kernels, linux‑azure kernel packages used by some Azure VM SKUs, Azure Marketplace images, AKS node images, appliance images, or other Microsoft‑distributed kernels) could also contain the same upstream code until each artifact is inventoried or patched. Treat Microsoft’s Azure Linux attestation as an authoritative “yes” for that product, and treat the absence of an attestation for other products as “unknown” rather than proof of absence.

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Technical validation and cross‑checks​

To ground this in independent facts, I cross‑checked the technical description and remediation across multiple distributor trackers:

• Ubuntu’s security notice describes the ext4 inline len overflow, reproducer, and the upstream fix (changing len parameter type). This corroborates the bug anatomy and the upstream remediation approach.
• AWS’s ALAS tracker and Amazon Linux advisories list the CVE, map it to kernel package updates across different kernel branches, and show the distribution‑level remediation cadence (some older branches are fixed later or not planned). This confirms distributors patched the issue on vendor‑timelines.
• Additional vulnerability trackers (Snyk, INCIBE, Positive Technologies) list the same behavior and confirm that the bug is in fs/ext4/inline.c and that the fix replaces the unsigned int with loff_t for len handling.

When multiple reputable sources independently describe the defect, call stacks, and the fix commit approach, we obtain high confidence in the technical facts used for triage and remediation.

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Why defenders should not assume exclusivity​

There are several practical reasons the attestation for Azure Linux should not be read as a global guarantee:

• Reuse and rebuilds: The same upstream kernel code can be embedded in many different downstream kernels via backports or rebuilds. A Microsoft WSL2 kernel, a linux‑azure kernel package, or a Marketplace VM image might have been built from a kernel tree that predates the upstream fix and therefore could contain the same buggy ext4 path.
• Distribution of compiled artifacts: Microsoft publishes multiple kernel artifacts (source trees, binary kepackages for Azure VM images). Unless each artifact is enumerated in a VEX/CSAF document, its status remains unverified.
• Customized backports: Enterprise kernels and vendor kernels commonly backport fixes, meaning that a kernel version number alone does not always indicate the presence or absence of a particular upstream commit. The only reliable method is artifact‑level verification: check the exact kernel commit, the patchset applied, or the vendor advisory mapping.

These realities create a “long tail” of artifacts that can remain unpatched or un‑mapped after a vendor publishes a product attestation for a primary product family.

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How to determine whether your Microsoft‑supplied artifacts are affected (practical steps)​

Below is a prioritized, actionable checklist you can use across your estate to verify exposure to CVE‑2025‑38222.

• Inventory Microsoft artifacts you run (images, kernels, WSL kernels, Marketplace images, unmanaged VM images).
• For each artifact, collect the kernel version and exact build provenance. Prefer:
• Exact kernel package name and package version (for packaged images).
• The kernel git commit ID used as the build input (when published).
• The WSL2 kernel source version if you use Microsoft’s WSL kernel binaries.
• Map your kernel version/commit to the upstream fix commit(s) for the ext4 inline len issue. If the upstream fix commit is present or the vendor advisory lists a fixed package version, mark the artifact as patched. If not, mark it as vulnerable.
• If you cannot obtain build provenance, perform an active verification:
• Boot a test instance and check kernel config / compile flags that indicate ext4 inline_data support.
• Run uname -a and compare to vendor advisory mappings.
• Grep for the function or check kernel sources (if available) to see if the loff_t change is present.
• For managed or vendor images where you cannot directly inspect kernel builds, rely on the vendor’s CSAF/VEX feed or security advisory mapping (and push the vendor to expand attestations when you need coverage of additional artifacts).
• When patching is not immediately possible, apply mitigations:
• Restrict untrusted local users where possible.
• Disable ext4 inline_data feature on filesystems that can be repartitioned and recreated without service disruption, if that is practical in your environment (this is a disruptive mitigation and not always feasible).
• Monitor kernel oops/panic logs and set host restart thresholds appropriately.

This methodical approach produces auditable evidence and lets you apply a risk‑based prioritization: start with Azure Linux images (confirmed carrier), then progress to other Microsoft artifacts in order of exposure ainfrastructure nodes, WSL instances used for CI, Marketplace images used by production workloads).

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Operational guidance: patching and triage​

• Prioritize Azure Linux images immediately. Microsoft’s attestation means Azure Linux customers have a definitive signal to drive patching and remediation automation for those images. Confirm the exact kernel vendor patch or upgrade to a kernel package that the vendor lists as fixed.
• For other Microsoft artifacts, perform the artifact‑level verification steps above. If you discover that some artifacts are built from vulnerable kernel branches, treat them the same as non‑Azure Linux artifacts — schedule remediation per business risk and exposure.
• Use machine‑readable VEX/CSAF feeds to automate triage where possible. Microsoft committed to publishing CSAF/VEX attestations beginning in October 2025; rely on t produced and cross‑check them against your inventory.
• Maintain robust logging and crash monitoring. Kernel stability issues often manifest as oops/panic traces in syslog/dmesg. Correlate such events with deployed workloads and apply containment controls to critical node groups if repeated kernel oops are observed.

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Risk analysis: strengths and notable risks of Microsoft’s attestation model​

Strengths​

• Transparency and machine‑readable attestations are operationally powerful. Publishing CSAF/VEX attestations for Azure Linux gives automation engines immediate, high‑confidence signals for that product family.patch for confirmed carriers and improves customer trust in vendor remediation processes.
• Product‑level attestation enables targeted remediation for the largest shared image family a vendor ships (Azure Linux), which is where many cloud customers have the greatest exposure.

Risks and limitations​

• Scoped coverage: an attestation naming a single product family cannot be used to infer absence across other artifacts. The long tail of images, WSL kernels, Marketplace appliances, and vendor-provided kernels may remain un‑mapped and therefore pose hidden operational risk.
• Dependence on completeness of vendor inventories: if a vendor’s inventory process is incomplete or delayed, customers must assume an “unknown until verified” posture for un‑attested artifacts.
• Potential mismatch between kernel version number and backported fixes: kernel package versioning and vendor backports complicate automated mapping; only an explicit vendor advisory or commit‑level check can guarantee presence of the fix. Distribution advisories (Ubuntu, Amazon Linux, Red Hat) remain essential cross‑checks for the same reason.

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When claims are unverifiable (and how to treat them)​

Any claim that “Azure Linux is the only Microsoft product affected” is unverifiable unless Microsoft explicitly attests that every Microsoft‑distributed kernel artifact does not include the implicated code. Microsoft’s attestation covers Azure Linux and a pledge to expand the mapping; it does not assert exclusivity. Treat any such exclusivity claim with caution, and require artifact‑level checks before concluding non‑exposure.

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Practical checklist for administrators (quick reference)​

• If you run Azure Linux:
• 1) Check your kernel package against Micapply the vendor package/patch immediately.
• 2) Reboot nodes as required by your vendor’s guidance and verify successful kernel upgrade.
• If you run other Microsoft images (WSL, Marketplace images, linux‑azure kernels):
• 1) Enumerate image origins and kernel provenance.
• 2) Map to upstream fixes or ask your vendor contact for CSAF/VEX attestations covering those artifacts.
• If you cannot patch immediately:
• Implement access controls to restrict untrusted local users.
• Consider temporary filesystem configuration changes or node isolation where practical.
• Automate:
• Ingest Microsoft’s CSAF/VEX outputs and relevant distro advisories into your vulnerability management workflows.
• Schedule re‑checks; vendor attestations and mapping may be updatoft expands coverage.

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Conclusion​

Microsoft’s public wording that “Azure Linux includes this open‑source library and is therefore potentially affected” is an important and actionable attestation: it confirms Azure Linux as a known carrier and gives Azure Linux customers a clear signal to patch. However, the statement is deliberately scoped: it is not a blanket declaration that no other Microsoft product could ever include the same vulnerable ext4 code. Defenders must treat Azure Linux as confirmed in‑scope and perform artifact‑level verification for other Microsoft kernels and images (WSL2 kernels, linux‑azure packages, Marketplace images, AKS node images, custom appliance images). Practical remediation depends on a mix of vendor advisories, kernel commit mapping, and active artifact inspections; use Microsoft’s CSAF/VEX feeds as they appear, cross‑check with distributor advisories (Ubuntu, Amazon Linux, etc.), and apply the prioritized patching and mitigation steps described above to reduce your exposure.

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Source: MSRC Security Update Guide - Microsoft Security Response Center