Azure Linux Attestation and CVE-2025-22125: What It Means

Microsoft’s brief advisory that “Azure Linux includes this open‑source library and is therefore potentially affected” is accurate — but it is a product‑scoped attestation, not a categorical statement that no other Microsoft product could include the same vulnerable md/raid1,raid10 code.

Background / Overview​

The vulnerability tracked as CVE‑2025‑22125 is a Linux kernel bug in the device‑mapper RAID code (md/raid1 and md/raid10) where the RAID layers were dropping important IO flags (for example REQ_IDLE, REQ_META, REQ_NOWAIT) when constructing the underlying bios. That behavior can throttle IO unexpectedly, reverse intended IO priorities, or change failure semantics — producing degraded throughput, stalled IO, or availability impacts under certain workloads. The upstream fix preserves the IO flags from the master bio so per‑request semantics are retained. Independent vulnerability trackers and distribution advisories catalogue the issue and link to the upstream patch set. Microsoft’s public CVE entry for this issue explicitly states that Azure Linux includes the implicated open‑source component and is therefore potentially affected, and the company has announced a phased rollout of machine‑readable CSAF/VEX attestations (starting with Azure Linux) and committed to update CVE/VEX mappings if additional Microsoft products are identified as carriers. That Microsoft wording is deliberate: it reports the result of Microsoft’s inventory work for the Azure Linux product family at publication time, and promises to expand the attestation set as more artifacts are inventoried.

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What Microsoft actually said — precise reading and why it matters​

• Microsoft’s statement is an authoritative product attestation for Azure Linux: it confirms Microsoft inspected and found the upstream md/raid code in Azure Linux images and therefore those images must be treated as in‑scope for remediation.
• The statement is not an explicit denial that other Microsoft products cannot include the same code. Absence of a VEX/CSAF attestation for other Microsoft SKUs is not proof they are free of the component; it simply means Microsoft has not yet completed that product’s inventory and published an attestation for it.
• Microsoft’s transparency work — publishing CSAF and VEX artifacts — is intended to reduce ambiguity by telling customers exactly which Microsoft artifacts have been checked and what the vendor found. But the rollout is phased: Azure Linux was the initial, easiest target to inventory and publish. Expect additional attestations over time.

These three points are the crux: treat Microsoft’s Azure Linux attestation as an authoritative yes for Azure Linux; treat everything else as unknown until proven otherwise.

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Technical snapshot: what CVE‑2025‑22125 is and why it matters​

The defect concerns how the md layer forwards IO to underlying devices:

• Root cause: When md/raid1 and md/raid10 assembled the lower‑level bio for a strip of a logical RAID IO, some IO flags were cleared or ignored rather than being propagated from the master bio. This included flags such as REQ_IDLE, REQ_META, and REQ_NOWAIT, each of which carries subtle but important semantics: REQ_IDLE affects write throttling behavior under blk‑wbt, REQ_META signals metadata priority semantics, and REQ_NOWAIT changes whether the lower layer should block or fail the IO immediately. Upstream patches preserve these flags when constructing the sub‑bios.
• Practical impact: In environments where blk‑wbt (block writeback throttling) is enabled by default, clearing REQ_IDLE can cause all RAID writes to be treated as idle — massively throttling throughput — or conversely remove intended prioritization. Clearing REQ_NOWAIT changes whether IOs fail fast or block, which can change error handling and availability semantics. Vendors characterize the issue primarily as an availability/performance problem.
• Exploitation vector: The issue is local; it doesn’t create a remote code execution primitive on its own. However, the operational impact can be meaningful in multi‑tenant hosts, hypervisor guests, or any service where untrusted workloads can trigger high IO or manipulate IO flags. Distributors backported fixes into stable kernels and published package mappings.

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Is Azure Linux the only Microsoft product that includes the library and is potentially affected?​

Short answer: No — not necessarily.
Long answer: Microsoft has publicly attested that Azure Linux includes the implicated upstream md/raid code and is therefore potentially affected; that attestation is authoritative and actionable for Azure Linux customers. But that assertion is a statement about Microsoft’s inventory for Azure Linux only at the time of publication — it does not prove that no other Microsoft product or image includes the same upstream kernel code.
Why the distinction matters:

• Microsoft builds and ships multiple Linux kernel artifacts and images that are separately built and packaged:
• Azure Linux (the Azure‑tailored CBL‑Mariner lineage images that Microsoft curates) — attested.
• linux‑azure / kernel‑azure builds used by some Azure VM images — these are separate artifacts that can include different kernel versions/configurations and may carry the same md code. Canonical’s linux‑azure package demonstrates Microsoft‑specific Azure kernel builds are in wide use.
• WSL2 kernel (Microsoft‑maintained kernel for Windows Subsystem for Linux) — Microsoft maintains a kernel repo for WSL2 which can and does receive upstream merges; a vulnerable commit could appear there depending on the branch, configuration, and timing.
• Marketplace, Partner, and custom images hosted in Azure Marketplace — those images may be built by publishers other than Microsoft and may embed kernels or modules that contain the code.
• CBL‑Mariner derivatives used in various Microsoft services or appliances — separate build pipelines can diverge in CONFIG_* and backports.
• Whether a specific Microsoft artifact is affected depends on two build‑time/runtime facts:
• The kernel commit range / upstream version used for the build (pre‑fix vs post‑fix).
• The kernel configuration (CONFIG flags) — whether md/raid is compiled in or present as a module.
• Microsoft’s VEX/CSAF rollout makes the inventory explicit as it completes for product families; Azure Linux is first in the initial rollout. Until Microsoft publishes an attestation for another product, that product’s status is unknown — not conclusively “not affected.”

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Cross‑checks and independent confirmation​

• The vulnerability and upstream fixes are recorded in NVD and in multiple distributor trackers (Ubuntu, Debian, Red Hat secondary trackers), which confirm the technical summary and list stable kernel commits that include the fix. These independent confirmations validate the bug description and the intended remedy.
• OSV and other open vulnerability databases point to the upstream git commits (stable backports) that resolve the problem — that commit trail is the primary evidence for whether a kernel build is fixed or not. Use those commits to map shipped kernel versions to fixed/unfixed status.
• Microsoft’s published VEX/CSAF program and blog post confirm the procedural approach: publish machine‑readable attestations starting with Azure Linux and expand coverage over time. That is Microsoft’s formal change in disclosure practice and explains why certain product families are listed first.

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How to confirm whether your Microsoft artifact (or any Linux host) is affected — a pragmatic checklist​

These are the most reliable, artifact‑level checks to determine exposure. Run them on the host or image you manage.

• Identify the running kernel and distribution metadata:
• uname -a
• cat /etc/os-release
• Map kernel version to upstream commits:
• Check the vendor/distributor advisory for the CVE and confirm whether your kernel package/version matches a vulnerable range or a fixed backport. Distributor advisories (Ubuntu, Debian, Amazon, SUSE) list package‑level mappings.
• Verify whether the md/raid code and relevant flags are enabled in the kernel:
• If /boot/config-$(uname -r) exists: grep -E 'CONFIG_MD|CONFIG_BLK_WBT' /boot/config-$(uname -r)
• Else if /proc/config.gz exists: zcat /proc/config.gz | grep -E 'CONFIG_MD|CONFIG_BLK_WBT'
• Look for CONFIG_MD, CONFIG_MD_RAID1, CONFIG_MD_RAID10, and blk‑wbt settings.
• Inspect loaded modules and md device state:
• lsmod | egrep 'md|dm_mod'
• cat /proc/mdstat
• mdadm --detail /dev/mdX (for any existing RAID devices)
• If the kernel is provided as a package (apt/yum/zypper):
• Query the package version and compare it to the distributor’s fixed version list (Ubuntu’s CVE page and Debian security tracker are good starting points).
• For images and artifacts you cannot boot locally (Marketplace images, WSL kernels):
• Inspect the kernel package or container image manifest if available.
• For WSL2: check the WSL kernel version and the WSL2 kernel repo branch used by your host; Microsoft’s WSL kernel is publicly visible and updated via Microsoft channels.
• Automate this inventory:
• Ingest Microsoft’s CSAF/VEX outputs (MSRC provider metadata) and cross‑reference the product SKUs you run.
• Use image scanning or EDR inventory to correlate running kernel strings with vendor‑published fixed versions.

These checks are the only definitive way to tell whether a build includes the vulnerable commit or not — an attestation is useful, but an artifact inspection is conclusive.

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Immediate operational guidance and remediation priorities​

• If you run Azure Linux images: treat the MSRC attestation as a confirmed in‑scope signal and prioritize patching or image replacement per Microsoft’s guidance. Azure images that are attested as “Known Affected” should be updated immediately.
• For other Microsoft artifacts (WSL kernels, linux‑azure images, Marketplace images, CBL‑Mariner derivatives):
• Do not assume they are unaffected. Run the artifact‑level checks above and prioritize remediation where the kernel version/config shows exposure.
• If you host multi‑tenant workloads (cloud VMs, CI runners, container hosts), prioritize hardening and patching because local attack vectors are more plausible in shared environments.
• If patching is delayed:
• Restrict access to host IO devices and limit untrusted workloads’ ability to issue heavy IO loads.
• Isolate hosts running unpatched kernels from sensitive services when possible.
• Automate detection:
• Ingest Microsoft’s CSAF/VEX files as they are published and correlate them with your asset inventory. Microsoft’s blog notes this exact use case for VEX: to give deterministic, machine‑readable mappings of product‑level exposure.

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Critical analysis — strengths and potential risks in Microsoft’s approach​

Strengths​

• Deterministic signal for Azure Linux: Microsoft’s VEX/CSAF attestations provide machine‑readable, authoritative statements that let automation systems decide at scale whether a named Microsoft product is affected. That eliminates guesswork for customers running those images.
• Phased rollout is pragmatic: Starting with Azure Linux — a Microsoft‑built, centrally managed distribution — is a low‑friction place to validate pipelines, and it delivers immediate benefit to cloud customers who run those images.
• Public commitments to expand: Microsoft has explicitly said it will update CVE/VEX entries if additional products are later found to ship the component, which provides an accountable process for expanding coverage.

Risks and gaps​

• Attestation ≠ exhaustiveness: The biggest operational hazard is interpreting an attestation for one product as an implicit assurance for all Microsoft artifacts. That is not how the program works; vendors with many build pipelines must inventory product families one‑by‑one. Absence of attestation for a product is unknown, not safe.
• Static/embedded artifacts remain blind spots: Statically linked binaries, appliance images, or partner Marketplace images may include vulnerable code without being covered by Microsoft’s attestation — those require publisher‑level inventory.
• Timing gap between disclosure and full coverage: Phased VEX rollouts inevitably produce a window where some Microsoft artifacts have been inventoried and others have not. During that window, defenders must run artifact checks rather than rely solely on vendor attestations.

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Recommended playbook (concise, ranked steps)​

• Patch Azure Linux instances immediately if Microsoft has attested them as affected.
• Inventory other Microsoft artifacts you run (WSL2 clients in developer fleets, Azure VM images using linux‑azure, Marketplace images) and run the artifact checks above.
• Automate ingestion of MSRC CSAF/VEX and your distributor advisories into your vulnerability management system to detect changes quickly.
• For hosts you cannot patch immediately, reduce attack surface: limit access to IO devices, restrict untrusted user workloads, and consider temporary policy controls to prevent intense IO storms from untrusted processes.
• Track upstream stable commit references and vendor backport notes to prove remediation (the git.kernel.org commits are the canonical patch references).

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Conclusion​

Microsoft’s MSRC entry that “Azure Linux includes this open‑source library and is therefore potentially affected” is an accurate and useful product attestation — and it is the right actionable signal for customers who run Azure Linux images. However, it is not a global guarantee that no other Microsoft product can include the same md/raid1,raid10 code. Kernel artifacts are an artifact‑level property: whether md/raid code appears in a specific product depends on the kernel commit range and the kernel configuration used when that product was built. Until Microsoft publishes additional VEX/CSAF attestations, other Microsoft artifacts (for example linux‑azure kernels, WSL2 kernels, Marketplace/partner images, or CBL‑Mariner derivatives) should be treated as unknown and verified through artifact‑level checks. Operationally: act now on the Azure Linux attestation; concurrently, inventory and verify every Microsoft‑supplied image and kernel you run; and automate ingestion of VEX/CSAF outputs so you detect future attestation updates the moment Microsoft publishes them. The vulnerability itself is well documented across upstream and distributor trackers — use the upstream commit IDs and the vendor package mappings to confirm whether a given kernel build is fixed. For defenders, the defensible posture is simple: trust the attestation as definitive for the named product, but treat absence of attestation as absence of evidence, not as evidence of absence.

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Source: MSRC Security Update Guide - Microsoft Security Response Center