CVE-2025-38399: Understanding Azure Linux Attestation and Microsoft Coverage Limits

Microsoft’s security note that “Azure Linux includes this open‑source library and is therefore potentially affected” is accurate — but it is a product‑level attestation, not proof that no other Microsoft product can include the vulnerable code; Azure Linux is simply the only Microsoft product Microsoft has publicly inventory‑checked and published as “potentially affected” so far.

Background / Overview​

CVE‑2025‑38399 is a Linux kernel bug in the SCSI target subsystem: a NULL pointer dereference in core_scsi3_decode_spec_i_port that can be triggered when an error path calls core_scsi3_lunacl_undepend_item with a potentially unset dest_se_deve pointer. The upstream fix is a defensive NULL check in the error path to prevent the kernel from dereferencing a NULL pointer. Vendor and distribution trackers mapped the upstream patch into their advisories and kernel updates shortly after the fix was merged into the stable trees. Multiple distributors (Debian, Ubuntu, Oracle, Amazon Linux, Red Hat and others) published CVE mappings and patch statuses for their kernel packages, underscoring that this is an upstream kernel defect addressed via normal upstream-to-distribution maintenance. Why this matters operationally: the bug is a kernel robustness issue with an availability impact. A NULL dereference in kernel space typically yields an oops or kernel panic — a denial‑of‑service condition — rather than a straightforward remote code execution primitive. The practical exploit vector is local or depends on the ability to present crafted SCSI/protocol inputs to a target that exposes the affected target_core_mod paths.

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Microsoft’s statement, VEX/CSAF rollout, and what “includes” means​

Microsoft’s Security Response Center (MSRC) entry for this CVE contains a short attestation: Azure Linux includes the implicated open‑source component and is therefore potentially affected. Microsoft also stated that it began publishing machine‑readable CSAF/VEX attestations in October 2025 and that it will update CVE records if additional Microsoft products are identified as carriers. That combination — a product‑specific attestation plus a pledge to expand mapping — is the key context to read Microsoft’s wording correctly.
Two concise takeaways about vendor VEX/CSAF attestations:

• Attestation is product‑scoped and procedural. It records the result of the vendor’s inventory for the named product family (in this case, Azure Linux). It confirms Microsoft inspected Azure Linux artifacts and found the upstream component there.
• Attestation is not an exclusion for other artifacts. Absence of a VEX entry for another Microsoft product does not prove that product is free of the vulnerable component; it simply means Microsoft has not yet published an inventory result for that product. Microsoft explicitly committed to update CVE/VEX records if other Microsoft products are later discovered to include the same library.

Thus, Microsoft’s sentence should be read as “we have inventory‑checked and found the component in Azure Linux” rather than “only Azure Linux could include it.”

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Technical anatomy: what the upstream record shows​

The upstream kernel description and stable‑tree commits clarify the defect and the fix:

• The problem occurs in the SCSI target code path: an error branch in core_scsi3_decode_spec_i_port unconditionally calls core_scsi3_lunacl_undepend_item with dest_se_deve, which may still be NULL in some error scenarios.
• The fix is straightforward and low‑risk: add a NULL check before calling core_scsi3_lunacl_undepend_item, converting a crash into a safe error path.

Independent trackers (NVD, distro security advisories and industry vulnerability databases) reproduced the same description and classified the issue as a moderate/important kernel availability problem, reflecting consensus across upstream and downstream channels.

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

Short answer: No — not necessarily. Azure Linux is the only Microsoft product Microsoft has publicly attested to include the implicated upstream code so far, but that attestation is limited to the artifacts Microsoft has inventory‑checked and published in its CSAF/VEX feed. Other Microsoft‑distributed artifacts could include the same code depending on kernel version, build configuration, and packaging choices.
Why that nuance is important:

• Microsoft maintains multiple distinct Linux artifacts and images, each built independently:
• Azure Linux (the attested product).
• linux‑azure kernels used for some VM SKUs.
• The WSL2 kernel image that ships with Windows.
• Curated Marketplace images and partner/appliance images.
• AKS node images and other container/VM host images.
• The presence of an upstream source file in a repository is distinct from compiling it into a shipped kernel; kernel CONFIG options, module choices, and backports determine whether a given feature or driver is present in a binary artifact. Two kernels built from the same upstream tree can differ dramatically.

Put plainly: the attestation is an authoritative “yes” for Azure Linux; for other Microsoft products the correct state is “unknown until inventory‑checked.” Microsoft has publicly committed to update the VEX/CSAF records as it expands coverage.

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Cross‑validation: independent evidence that this is an upstream kernel issue (why this matters for non‑Azure Linux users)​

Multiple independent sources corroborate the upstream kernel description and the fact that distributors are mapping the fix into their kernels:

• NVD and public CVE aggregators show the same defect summary and fixed commit details.
• Vendor trackers (Amazon Linux ALAS, Debian/Ubuntu advisory summaries, Oracle Linux) list affected kernel packages and fix status across distributions. These vendor advisories show the defect is not specific to a single distribution — it is a general Linux kernel fix that distributors must absorb and ship.

This multi‑vendor corroboration matters because Microsoft’s attestation about Azure Linux is a product‑scoped statement; the underlying vulnerability exists in upstream Linux and therefore can appear in any Microsoft image or kernel that incorporated the affected commits without the fix.

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Practical verification — how to tell whether your Microsoft artifact is affected​

Administrators should treat Microsoft’s VEX/CSAF attestation for Azure Linux as an authoritative signal for Azure Linux images, and they should perform artifact‑level verification for any other Microsoft artifacts they run. The following runbook is designed to be concise and automatable.

Quick inventory and triage (high priority)​

• Identify Microsoft Linux artifacts in your estate:
• Azure VM images (including Azure Linux).
• Marketplace images and prebuilt appliances from Microsoft.
• AKS node images and node pools.
• Windows hosts running WSL2 (the WSL2 kernel is a Microsoft‑maintained kernel image).
• Any automation pipelines that build or ship Microsoft images.
• Prioritize Azure Linux artifacts immediately because Microsoft attested them as potentially affected.

Artifact‑level checks (commands you can run on a representative host)​

• Check kernel version:
• uname -r
• Inspect kernel package changelog and vendor advisory:
• For RPM systems: rpm -q --changelog kernel | grep -i CVE-2025-38399
• For Debian/Ubuntu: apt changelog linux-image-$(uname -r) | grep -i CVE-2025-38399
• Inspect kernel config for target_core_mod / SCSI target settings:
• zcat /proc/config.gz | grep -E 'TARGET_CORE|SCSI|TARGET' or
• grep -i 'CONFIG_TARGET' /boot/config-$(uname -r)
• Check loaded modules and dmesg for target_core_mod signs:
• lsmod | grep target
• dmesg | grep -i 'target_core_mod|target'
• If you build kernels from source, verify the upstream commit appears in your tree:
• git log --grep='core_scsi3_decode_spec_i_port' or search for the NULL check in target/target_core_mod files.
• If SBOMs are available for images, parse them for the kernel package version or the target_core_mod module; if MSRC/VEX lists product IDs, map those to your image SKUs.

Automation and fleet scale​

• Script the above checks for a representative sample of hosts and images, surface hosts with matching kernel package versions or module presence, and treat those as in‑scope for patching if the vendor advisory maps the fix to that package version.
• Use image scanning and SBOM tooling to inventory shipped images across cloud/edge hosts.
• If you cannot directly verify a Microsoft image SKU, open a support ticket with Microsoft referencing the CVE and asking whether the specific SKU or kernel build is inventory‑checked in their VEX feed; Microsoft committed to update CVE/VEX records as inventory expands.

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Mitigation and remediation guidance​

• Primary remediation: install the vendor’s patched kernel package that includes the upstream fix and reboot hosts. Distribution advisories (Amazon ALAS, Debian, Ubuntu, Oracle, Red Hat) list the fixed package versions and release dates.
• For Azure Linux: follow Microsoft’s remediation guidance for Azure Linux images — Microsoft’s VEX/CSAF and update guidance list the attested product and the remediation status. Treat Azure Linux images as in‑scope until the VEX record marks them fixed.
• Temporary mitigations: if target_core_mod (SCSI target functionality) is not required on certain hosts, consider unloading the module or removing the capability until you can deploy a patched kernel. This reduces local attack surface where SCSI target paths could be triggered. Note: unloading core kernel modules may not be possible on production hosts without service impact. Use with caution.
• Patch windows and reboots: because the fix is in kernel code, remediation requires kernel updates and a reboot. Plan maintenance windows accordingly.
• Monitoring and detection: enable and collect kernel logs (journalctl -k, dmesg), configure kdump/vmcore collection for hosts that experience oops/panics, and hunt for crash signatures that reference target_core_mod or the relevant call trace.

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Risk assessment and attacker model​

• Exploitability: the vulnerability is a NULL pointer dereference that causes kernel crashes; this is primarily an availability risk (DoS). Public trackers classify it accordingly, and there is no authoritative public evidence of a remote, unauthenticated RCE worm chain for this specific defect at time of disclosure.
• Threat vectors: local unprivileged code that can reach the affected SCSI target paths, crafted SCSI traffic presented to a target, or privileged processes that exercise the target_core_mod code could trigger the condition. In cloud or multi‑tenant environments, any kernel crash is high impact because it disrupts multiple tenants or services.
• Severity: vendor CVSS and severity assessments vary, but many vendors rated it moderate-to-important because of host availability implications and the local attack vector. Amazon ALAS reported a CVSSv3 score in the important range for affected Amazon Linux kernels.

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Organizational checklist: recommended actions today​

• Treat Azure Linux images as high‑priority: apply Microsoft’s updates or the distribution kernel patch for Azure Linux first because MSRC attested Azure Linux as potentially affected.
• Inventory other Microsoft artifacts that run Linux kernels (WSL2, linux‑azure, Marketplace images, AKS nodes) and run the verification runbook above to determine whether those artifacts include the vulnerable module or kernel package.
• Patch and reboot vulnerable hosts as vendor advisories become available for the kernel package you run. Use canary hosts and staged rollouts for large fleets.
• For images you distribute internally or to tenants (custom Marketplace appliances, baked images): rebuild with patched kernel packages and publish new image versions.
• Automate detection: add kernel oops / call‑trace signatures to your detection rules and alert on repeated target_core_mod crashes.
• If you cannot patch immediately, consider temporary mitigations: disable SCSI target functionality on hosts where it is not needed, and limit exposure to untrusted device inputs.

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Limitations and unverifiable claims (cautionary notes)​

• Microsoft’s MSRC entry for the CVE is rendered via a JavaScript application and some public pages may require interaction to fully view the VEX/CSAF JSON. The MSRC wording quoted — that Azure Linux “includes this open‑source library and is therefore potentially affected” — is a product‑scope attestation and is the authoritative statement for Azure Linux at the time of publication. When MSRC expands VEX coverage to additional products, it will publish updates accordingly.
• It is not possible to conclusively declare that no other Microsoft product includes the vulnerable code without a complete inventory of every Microsoft artifact and SKU. Any statement claiming exclusivity would be unverifiable until Microsoft publishes attestations for the entire product set or until you have inspected every artifact you depend on. Treat “no mention” as absence of attestation, not as evidence of absence.

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Final analysis and takeaways​

• Microsoft’s phrasing is deliberate and helpful: it tells defenders exactly what Microsoft has checked (Azure Linux), and it commits to expanding that mapping via CSAF/VEX. That improves automation and reduces uncertainty for Azure Linux customers.
• However, Microsoft’s attestation is not an organizational all‑clear for the rest of Microsoft’s product portfolio. The underlying defect is an upstream Linux kernel issue; any Microsoft artifact that ships a Linux kernel built from the affected upstream code could be a carrier until inventory‑checked and patched.
• Operational priority: treat Azure Linux as in‑scope immediately, then run artifact‑level verification and patch rollouts for other Microsoft images, WSL2 kernels, AKS nodes, and marketplace appliances you run or distribute. Use SBOMs, kernel package changelogs, and Microsoft’s VEX/CSAF outputs to automate triage where possible.

The pragmatic truth for defenders is simple: Microsoft’s attestation clarifies where the vendor has looked; it does not remove the need for artifact‑level verification. Prioritize Azure Linux per the attestation, but do not presume the rest of your Microsoft‑supplied Linux artifacts are clean — verify, patch, and monitor.

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Source: MSRC Security Update Guide - Microsoft Security Response Center