Microsoft’s brief CVE entry and product note is correct — Azure Linux (formerly CBL‑Mariner) has been identified as including the open‑source kernel component referenced by CVE‑2025‑38636 and is therefore “potentially affected” — but that product‑level attestation is not a proof that no other Microsoft product can or does include the same code. The phrase Microsoft published is an inventory statement for the named product family; the absence of other Microsoft SKUs from the VEX/CSAF output is absence of attestation, not evidence of absence.
CVE‑2025‑38636 is a Linux‑kernel tracepoint correctness issue: certain DA‑monitor tracepoints used by the rv/da monitor code read fixed 32‑byte arrays instead of variable‑length string literals, which under KASAN reveals a global out‑of‑bounds read. The bug manifests as a KASAN warning (global‑out‑of‑bounds reads in do_trace_event_raw_event_event_da_monitor) and is classified as a medium‑severity robustness issue rather than a direct code‑execution primitive. Upstream fixes change the tracepoint definitions to use __string so the kernel does not read past the string terminator. Microsoft’s Security Response Center entry for the CVE contains two linked claims you should read together: (1) Azure Linux includes this open‑source library and is therefore potentially affected, and (2) Microsoft began publishing machine‑readable CSAF/VEX attestations in October 2025 and will update the CVE/VEX entry if additional Microsoft products are found to ship the component. That second point is a commitment to phased, product‑by‑product transparency (Microsoft’s VEX rollout began with Azure Linux).
Microsoft’s move to publish VEX/CSAF attestations is a welcome improvement for enterprise security automation; it creates an authoritative “yes/no/under investigation/fixed” mapping for products like Azure Linux. That capability reduces guesswork. At the same time, operational reality — multiple product artifacts, different build pipelines, and statically embedded binaries — means that verification remains the customer’s responsibility outside of attested product families. Until Microsoft’s VEX feed expands to name additional SKUs explicitly, organizations should act on the Azure Linux attestation immediately and perform artifact‑level checks for the rest of their Microsoft‑supplied Linux footprint.
Source: MSRC Security Update Guide - Microsoft Security Response Center
Background / Overview
CVE‑2025‑38636 is a Linux‑kernel tracepoint correctness issue: certain DA‑monitor tracepoints used by the rv/da monitor code read fixed 32‑byte arrays instead of variable‑length string literals, which under KASAN reveals a global out‑of‑bounds read. The bug manifests as a KASAN warning (global‑out‑of‑bounds reads in do_trace_event_raw_event_event_da_monitor) and is classified as a medium‑severity robustness issue rather than a direct code‑execution primitive. Upstream fixes change the tracepoint definitions to use __string so the kernel does not read past the string terminator. Microsoft’s Security Response Center entry for the CVE contains two linked claims you should read together: (1) Azure Linux includes this open‑source library and is therefore potentially affected, and (2) Microsoft began publishing machine‑readable CSAF/VEX attestations in October 2025 and will update the CVE/VEX entry if additional Microsoft products are found to ship the component. That second point is a commitment to phased, product‑by‑product transparency (Microsoft’s VEX rollout began with Azure Linux). What the MSRC wording actually means
Product‑scoped attestation, not global exclusion
VEX/CSAF attestations are designed to deliver deterministic, machine‑readable answers about whether a vendor‑shipped product includes a particular component and what its exploitability status is. When Microsoft says a product “includes” a library and is “potentially affected,” that is a statement of inventory for that specific product family. It is authoritative for the named product (Azure Linux) and is intended to be consumed by automated triage systems. It is not, however, an exhaustive scan of every Microsoft image, kernel build, Marketplace appliance, or embedded binary Microsoft produces. Microsoft has explicitly said it will update those attestations as its inventory work expands.Why vendors publish VEX in waves
Large vendors routinely roll out VEX/CSAF in stages because product inventories are complex: images, kernels, containers, and appliances are distinct artifacts built at different times with different toolchains and configuration flags. Starting with a single product family — in Microsoft’s case, Azure Linux — allows the vendor to validate tooling and processes before broadening coverage. This is good for transparency, but it also creates a temporary window where customers must not assume that non‑attested products are necessarily not affected.Technical summary of CVE‑2025‑38636 (quick, verifiable facts)
- Affected component: kernel tracepoints in the rv/da monitors area (Linux kernel).
- Symptom: KASAN reports a global out‑of‑bounds read when DA monitor tracepoints read fixed 32‑byte arrays instead of string literals.
- Impact: correctness / robustness; KASAN warnings or kernel oopses under KASAN-enabled builds, potential reliability/diagnostic noise. The commonly reported impact is non‑exploitable in the sense of remote code execution, but still worth fixing to avoid undefined behavior and potential diagnostic corruption.
The short answer to the user’s question
No — Azure Linux is not necessarily the only Microsoft product that includes the affected open‑source kernel code, but Azure Linux is the only Microsoft product Microsoft has publicly attested (via VEX/CSAF) to include it so far. Treat Microsoft’s attestation as definitive for Azure Linux and as a prompt to verify other Microsoft artifacts you run. Absence of a VEX/CSAF mapping for another Microsoft product is not proof that product is safe.Why that nuanced answer matters operationally
Short, practical reasons why you cannot assume exclusivity:- Kernel inclusion is a build‑time property. Two kernels compiled from the same upstream sources can include different features depending on CONFIG_* flags.
- Microsoft ships multiple Linux artifacts:
- Azure Linux (attested).
- linux‑azure kernels used for certain Azure VM SKUs.
- Windows Subsystem for Linux (WSL2) — Microsoft builds and ships a tailored Linux kernel for WSL.
- Marketplace VM images and third‑party appliances hosted by Azure.
- Container base images, AKS node images, and curated platform images.
- Statically compiled or bundled binaries (or kernel modules packaged into appliances) can carry vulnerable code independent of the distribution package manager updates.
- Marketplace or partner images may be built by third parties and are not automatically covered by Microsoft’s Azure Linux attestation.
Evidence and independent verification
Key cross‑checks performed:- NVD and major distro trackers document the same root cause and remediation steps for CVE‑2025‑38636 (tracepoint reading array vs string). This confirms the technical description.
- Debian and Ubuntu vulnerability tracking pages list the CVE and reflect distribution packaging activity (backports / fixes) for kernels where applicable.
- OSV and other aggregator services show the CVE and downstream mappings.
- Microsoft’s public security update guidance and its VEX rollout blog show the company intentionally started publishing machine‑readable attestations with Azure Linux in October 2025 and committed to expand those attestations. That explains the phrasing in the CVE entry and sets expectations for updates.
- Windows Forum community analysis (uploaded evidence) unpacks Microsoft’s wording and consistently reaches the same operational conclusion: Azure Linux is attested; other Microsoft artifacts may be unverified until attested or inspected.
Practical verification and remediation checklist (actionable steps)
Below is a prioritized checklist IT teams can use to determine exposure and remediate across mixed Microsoft + Linux estates.- Inventory: locate Microsoft‑supplied Linux artifacts in your estate.
- Azure VM images: check the image publisher and SKU.
- AKS/managed node images: list node images and underlying base image references.
- Marketplace images and appliances: catalogue third‑party images pulled into your environment.
- WSL instances: enumerate Windows hosts with WSL2 enabled.
- Check kernel versions and builds:
- On Linux instances: run uname -r and compare kernel package versions against vendor/security tracker advisories.
- Check the kernel provenance for “linux‑azure” or “azl” kernels in Azure images.
- For WSL: run wsl --status and inside distro run uname -r to identify the WSL kernel version; Microsoft documents that WSL2 uses a Microsoft‑built kernel and supports wsl --update to apply kernel updates.
- Inspect SBOMs / VEX/CSAF outputs:
- Consume Microsoft’s CSAF/VEX feed (the provider metadata and product attestations) where available to determine “Known Affected / Not Affected / Under Investigation / Fixed” for named products. Microsoft published its VEX rollout blog and the provider metadata path.
- Where Microsoft has not provided VEX for a product, obtain or generate SBOMs for your images and appliances and scan them for matching kernel symbols, modules, or source versions.
- Search for KASAN or tracepoint errors:
- On systems built with KASAN (test/dev kernels), check dmesg or journalctl for “KASAN” warnings referencing do_trace_event_raw_event_event_da_monitor or similar tracepoint names.
- Apply fixes and test:
- For attested Azure Linux images: apply the vendor kernel updates Microsoft or the distro publishes and follow the vendor reboot/replace guidance.
- For WSL: run wsl --update and wsl --shutdown to apply the Store/MSIX WSL kernel update where applicable.
- For Marketplace images or third‑party appliances: obtain updated images from the publisher or rebuild locally with patched kernel sources.
- For statically embedded binaries or modules:
- Identify any statically compiled binaries (for example, vendor agents written in C/Go that embed parts of the kernel or rely on kernel headers) and rebuild them with safe sources if necessary.
- Replace or isolate vulnerable appliances until updates are available.
- Monitoring and policy:
- Integrate VEX/CSAF consumption into your vulnerability triage automation so Microsoft’s attestations are machine‑readable inputs to your prioritization logic.
- Maintain strict controls on Marketplace image provenance and automate image verification where possible.
Recommended prioritization (practical risk triage)
- Highest priority
- Systems running attested Azure Linux images or kernels: patch and reboot per vendor guidance immediately.
- WSL instances on developer machines where local fuzzing or untrusted code may trigger unusual kernel traces (apply WSL kernel updates).
- Medium priority
- Azure Marketplace or third‑party images used widely in your estate: verify vendor statements, request SBOMs, or temporarily replace with vendor‑patched images if available.
- AKS nodes and curated container images that embed custom kernels or kernel modules.
- Lower priority
- Consumer Linux distributions or appliances where the kernel feature in question is compiled out or the environment does not load the relevant tracepoints. This still requires verification — do not assume safety.
Strengths and benefits of Microsoft’s approach — why this is good news
- Machine‑readable attestations (VEX/CSAF) materially reduce the noise for large estates. Automation can treat an explicit “Known Affected” for Azure Linux as a deterministic triage input and remediate rapidly. Microsoft published a public blog explaining this phased rollout and the mechanics of VEX/CSAF.
- Publishing attestations increases transparency and reduces time wasted chasing uncertain vendor statements. A reliable VEX feed helps enterprise orchestration systems prioritize correctly.
- The CVE itself is a robustness fix rather than an immediate remote‑code execution vector; fixing reduces undefined behavior and avoids diagnostic confusion under KASAN.
Risks, blind spots, and remaining uncertainties
- Phased coverage risk: while Azure Linux is attested, other Microsoft artifacts remain unverified until Microsoft expands the VEX feed or a per‑artifact inspection is performed. This creates an operational blind spot in the short term.
- Marketplace and third‑party images: many customers consume Marketplace appliances or partner images that Microsoft hosts or distributes; those images can carry different build choices and may not be covered by Microsoft’s Azure Linux attestation. Treat each image as independently suspect until proven otherwise.
- Unverifiable artifact claims: without SBOMs or vendor attestations for a given image, claims about whether a Microsoft product besides Azure Linux includes the vulnerable component are unverifiable. That must be flagged in risk registers and treated as “unknown” rather than “safe.”
Sample commands and checks (quick reference)
- Check kernel on a Linux VM:
- uname -a
- rpm -q kernel || dpkg -l | grep linux-image
- Search for tracepoint names in kernel modules or dmesg:
- dmesg | grep -i da_monitor
- journalctl -k | grep -i KASAN
- WSL kernel checks:
- wsl --status
- wsl --update
- Inside a WSL shell: uname -r
- SBOM/VEX consumption:
- Pull Microsoft’s CSAF/VEX feed (provider-metadata.json) and check the product mappings (automation varies by environment).
Final assessment and recommendations
Microsoft’s public advisory is accurate and valuable: it gives Azure Linux users a clear, machine‑readable signal to act on. However, the advisory should not be read as a defense for complacency across other Microsoft artifacts. Operators must adopt a two‑track response:- Track A — Immediate: treat Azure Linux as in‑scope, patch per Microsoft/distro guidance, and validate remediation by testing updated kernels.
- Track B — Inventory and verify: enumerate other Microsoft artifacts you run (WSL, linux‑azure kernels, Marketplace images, AKS nodes). For each artifact, either (a) rely on vendor‑published VEX/CSAF attestations, or (b) perform artifact‑level inspection (SBOM, kernel version, module list) to determine exposure. Where the artifact cannot be verified, treat it as “unknown” and apply compensating controls (isolate, restrict access, or temporarily replace) until you can confirm the status.
Microsoft’s move to publish VEX/CSAF attestations is a welcome improvement for enterprise security automation; it creates an authoritative “yes/no/under investigation/fixed” mapping for products like Azure Linux. That capability reduces guesswork. At the same time, operational reality — multiple product artifacts, different build pipelines, and statically embedded binaries — means that verification remains the customer’s responsibility outside of attested product families. Until Microsoft’s VEX feed expands to name additional SKUs explicitly, organizations should act on the Azure Linux attestation immediately and perform artifact‑level checks for the rest of their Microsoft‑supplied Linux footprint.
Source: MSRC Security Update Guide - Microsoft Security Response Center
