Azure Linux CVE-2025-38275 Attestation: Scope and Mitigation

Microsoft’s public advisory confirms that Azure Linux images include the upstream open‑source kernel code referenced by CVE‑2025‑38275 and are therefore potentially affected, but it does not assert that Azure Linux is the only Microsoft product that contains the vulnerable component — the attestation is product‑scoped and Microsoft says it will expand the CVE notice if additional products are identified.

Background​

CVE‑2025‑38275 describes a kernel driver robustness issue in the Qualcomm QMP USB PHY path — a classic NULL vs IS_ERR error handling omission that can lead to a kernel NULL pointer dereference (availability impact). The upstream fix is typically a small, defensive check: validate a pointer returned from a helper (IS_ERR_OR_NULL or explicit NULL test) before dereferencing. Upstream maintainers have folded the fix into stable kernel branches and distributions are mapping or backporting the commit to their packaged kernels.
Microsoft’s published statement on this CVE explicitly calls out Azure Linux as including the open‑source library in question and therefore being “potentially affected.” Microsoft also highlighted their commitment to publishing machine‑readable CSAF/VEX attestations for Azure Linux to improve transparency about what open‑source components are present in their images. The statement stops short of declaring other Microsoft products unaffected, and Microsoft has pledged to update the CVE page if more products are found to include the same component.

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What Microsoft actually attested — and what that means​

The scope of the attestation​

• Microsoft’s attestation is product‑scoped: it covers Azure Linux images that Microsoft distributes and maintains. That means the company completed an inventory for that product family and confirmed the presence of the vulnerable code in those images.
• The attestation is not a catalogue of every Microsoft product or artifact. The absence of a Microsoft‑wide attestation should not be read as proof that other Microsoft products are immune; it simply means Microsoft has not (yet) published the inventory for those other products.

Plain language conclusion​

Because the attestation is limited to Azure Linux, Azure Linux is confirmed in‑scope, but it is not correct to read Microsoft’s statement as definitive evidence that no other Microsoft product contains the same open‑source library. Microsoft’s public posture — “we’ll update the CVE if additional products are identified” — explicitly leaves the possibility open that other artifacts may be affected.

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Technical context: why this class of kernel bug matters​

Kernel code frequently uses pointer-returning helpers that encode error information as either NULL or ERR_PTR values. When a caller assumes a helper always returns a valid pointer and fails to test for NULL or IS_ERR, a kernel NULL dereference or an invalid pointer dereference can occur. In privileged, kernel‑mode context this commonly results in an oops, panic, or other host‑wide instability — an availability problem rather than immediate data disclosure or guaranteed code execution. The upstream remediation pattern is well understood: add an IS_ERR_OR_NULL or NULL guard and gracefully propagate the error instead of dereferencing.
Practical exposure models for such defects:

• Local or local‑adjacent: an attacker usually needs to be able to attach or present a crafted device (e.g., USB device) or to run code that exercises the kernel driver.
• Cloud / virtualization considerations: USB passthrough or device emulation in virtual environments can create a local‑adjacent attack surface where an attacker in a guest or a host can cause the path to execute.
• Embedded and vendor kernels: devices that ship long‑tail kernel forks or delayed backports are often the highest risk population because they may not receive the upstream fix promptly.

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Is Azure Linux the only Microsoft product that includes the library?​

Short answer: No — Azure Linux is the only Microsoft product Microsoft has publicly attested to so far, but that does not mean it is the only Microsoft product that could include the same vulnerable open‑source library. Microsoft’s attestation confirms Azure Linux images are in‑scope; it does not provide negative proof about other products. The company explicitly said it will update the CVE when impact to additional Microsoft products is identified.
Why that conclusion is warranted:

• Microsoft performed and published a targeted inventory for Azure Linux and issued a product‑scoped attestation. That inventory is authoritative for that product family.
• Microsoft did not publish a simultaneous, company‑wide inventory covering other artifacts (WSL kernels, Marketplace images, vendor tools, internal builds). The absence of those attestations is not evidence of absence — it is simply that those inventories were not reported in this advisory window.
• Microsoft has stated an intent to update the CVE record if further products are affected, which indicates their analysis is ongoing or staged. Treat the current attestation as an initial product‑scoped disclosure rather than a final, company‑wide declaration.

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How customers and defenders should respond (practical playbook)​

Operators who run any Microsoft‑provided Linux artifacts (Azure Marketplace images, WSL2 kernels, CBL‑Mariner‑based builds, or vendor images) should treat Microsoft’s Azure Linux attestation as a high‑priority signal but not the only source of truth. Follow these prioritized steps:

• Inventory Microsoft‑supplied Linux artifacts you run:
• Locate all Azure Marketplace images, WSL2 kernel binaries, Microsoft‑branded virtual machine images, and vendor images acquired from Microsoft channels.
• Treat Azure Linux images as confirmed in‑scope per Microsoft’s statement and prioritize them for immediate kernel verification and patching.
• Check running kernels and module presence:
• Run basic on‑host checks:
• uname -a
• cat /proc/version
• lsmod | grep <relevant_module_name>
• grep -i <driver_name> /boot/config-$(uname -r)
• Confirm whether the compiled kernel includes the vulnerable driver code paths. Practical examples and commands appear in vendor guidance and Microsoft‑adjacent advisories.
• Validate patch presence via package changelogs or commit IDs:
• Confirm your kernel package changelog explicitly references the upstream stable commit ID that fixed the condition, or that your vendor advisory lists the CVE and fixed package version.
• For Microsoft Azure Linux images, consult the CSAF/VEX attestation payload (machine‑readable) where Microsoft publishes component inventories and patch status for that product family.
• Apply the kernel updates and reboot:
• Kernel fixes require new kernel packages and a reboot unless a vendor provides a certified livepatch. Schedule test and production rollouts accordingly.
• If you cannot patch immediately, apply short‑term controls (disable USB passthrough, restrict untrusted device attach, blacklist the problematic module where feasible).
• For Microsoft customers running other Microsoft artifacts:
• Don’t assume those artifacts are safe. Map each artifact to its kernel provenance and apply the same verification checklist.
• If you cannot determine whether the artifact includes the vulnerable library, treat it as potentially affected until proven otherwise and prioritize mitigation.

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Detection and evidence gathering​

Because this class of defect produces kernel oopses and stability issues, detection focuses on kernel telemetry:

• Monitor dmesg and journalctl -k for oops/backtrace messages mentioning the driver symbols or generic NULL pointer dereference strings.
• Centralize and correlate kernel logs across hosts to spot repeated, correlated failures after device attach/detach events.
• For virtualization and cloud workloads, correlate guest/host attach events (USB passthrough) with kernel oopses.
• Keep vmcore/kdump enabled on critical systems to capture post‑mortem evidence for forensics and vendor escalation. Examples and guidance on detection patterns and telemetry are standard for kernel NULL/IS_ERR fix advisories.

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Critical analysis — strengths and gaps in Microsoft’s approach​

Strengths​

• Transparency for Azure Linux: Microsoft produced a targeted, machine‑readable attestation (CSAF/VEX) for Azure Linux. Publishing machine‑readable VEX artifacts is a positive step toward enabling automation and clear upstream mapping.
• Explicit commitment to update: Microsoft’s promise to update the CVE page if more products are impacted sets a clear, accountable path for expanding the scope as inventory work completes.

Potential gaps and operational risks​

• Product scope vs. corporate scope: The attestation covers only Azure Linux. Customers who run other Microsoft‑supplied artifacts (WSL kernels, Marketplace images, proprietary images) must not assume they are out of scope. Microsoft’s current statement does not guarantee those artifacts are unaffected; it only confirms inventory for Azure Linux. This distinction is critical for large, mixed estates.
• Lag between inventory and remediation: Even when an attestation proves a product is affected, remediation depends on distribution packaging and scheduling. Azure Linux being in‑scope does not equal immediate patch availability for every image — operators must validate package changelogs and apply updates.
• Communication cadence for other products: Microsoft’s pledge to update the CVE if additional products are identified is necessary but reactive; proactive, company‑wide component inventories published concurrently would reduce customer uncertainty.

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Verification checklist and escalation guidance​

• If you run Azure Linux images:
• Treat them as confirmed in‑scope and follow your normal kernel update process immediately. Confirm updates by package changelog that references the upstream fix.
• Use Microsoft’s CSAF/VEX output for Azure Linux to automate inventory checks where possible.
• If you run other Microsoft artifacts:
• Map the artifact to its kernel/package provenance.
• Apply the same verification steps: uname + package changelog + check for the upstream commit ID.
• If uncertain, assume potential exposure and apply mitigations (disable passthrough, blacklist module, isolate workload).
• Escalation path:
• If you confirm a Microsoft product beyond Azure Linux includes the vulnerable code, report it to Microsoft security channels and request VEX/CSAF updates for the artifact in question.
• If Microsoft does not respond or you require more urgent action for managed services, treat the host as vulnerable in your operational risk model and apply compensating controls.

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Recommendations for IT teams and security operators​

• Prioritize Azure Linux images for immediate verification and patching — Microsoft has explicitly inventoried them and flagged potential exposure.
• Don’t conflate attestation scope with product safety. Build automated checks that:
• Parse CSAF/VEX attestations where provided,
• Map binaries in images to upstream components and commit IDs,
• And alert when a known vulnerable component is present in any image, regardless of vendor branding.
• Harden device attach vectors in the short term: limit USB passthrough, enforce device allowlists, and disable unneeded kernel modules on hosts that do not require the affected drivers.

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Final assessment​

Microsoft’s public attestation correctly identifies Azure Linux as including the vulnerable open‑source library referenced by CVE‑2025‑38275 and therefore potentially affected. That attestation is a useful, authoritative signal for operators who use Azure Linux images. However, it is not a blanket statement about all Microsoft products. The attestation is product‑scoped; other Microsoft artifacts may still include the same upstream code, and Microsoft has committed to updating the CVE entry should further products be found to contain the vulnerable component. Treat Microsoft’s Azure Linux attestation as a confirmed in‑scope finding for that product, and continue to inventory and verify all other Microsoft‑supplied artifacts in your environment rather than assuming they are unaffected.

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This analysis synthesizes the public attestation language and standard kernel remediation patterns and provides a practical, verifiable playbook to help teams find and fix exposure across Microsoft‑provided Linux artifacts and mixed estates.

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Source: MSRC Security Update Guide - Microsoft Security Response Center