The Microsoft Security Response Center’s short FAQ line — “Azure Linux includes this open‑source library and is therefore potentially affected” — is accurate for the Azure Linux family, but it is not a categorical guarantee that no other Microsoft product can contain the same vulnerable Linux Bluetooth code. Treat Azure Linux as a confirmed, high‑priority carrier to patch, and treat other Microsoft artifacts as unverified until you confirm them by artifact inspection or Microsoft updates its VEX/CSAF attestations.
CVE‑2025‑38117 is an upstream Linux kernel fix that addresses a concurrency/synchronization bug in the Bluetooth management (MGMT) code: the mgmt_pending list was not protected by its own mutex, which allowed concurrent access paths to race and in some reproductions produced KASAN slab-use-after-free traces and kernel crashes. The upstream announcement and stable‑branch backports document the fix and provide the kernel-level context for the problem.
Microsoft’s public CVE entry for this issue takes the now-common vendor approach of publishing a short, product‑scoped attestation: it confirms Azure Linux (the Microsoft‑maintained Linux distribution formerly known as CBL‑Mariner) includes the implicated upstream component and is therefore potentially affected. Microsoft also notes it began publishing machine‑readable CSAF/VEX attestations in October 2025 and will update CVE mappings if it discovers additional affected Microsoft products. That phrasing is deliberate: it is precise about what Microsoft has inspected to date, but it is not an exclusionary claim about the entire Microsoft product portfolio.
This article explains what that short MSRC sentence actually means, what other Microsoft artifacts could — technically and practically — be carriers of the same upstream BlueZ/MGMT code, how you should verify whether systems you manage are affected, and which mitigation and prioritization steps are appropriate.
Two concrete operational risks to be aware of:
Source: MSRC Security Update Guide - Microsoft Security Response Center
Background / Overview
CVE‑2025‑38117 is an upstream Linux kernel fix that addresses a concurrency/synchronization bug in the Bluetooth management (MGMT) code: the mgmt_pending list was not protected by its own mutex, which allowed concurrent access paths to race and in some reproductions produced KASAN slab-use-after-free traces and kernel crashes. The upstream announcement and stable‑branch backports document the fix and provide the kernel-level context for the problem.Microsoft’s public CVE entry for this issue takes the now-common vendor approach of publishing a short, product‑scoped attestation: it confirms Azure Linux (the Microsoft‑maintained Linux distribution formerly known as CBL‑Mariner) includes the implicated upstream component and is therefore potentially affected. Microsoft also notes it began publishing machine‑readable CSAF/VEX attestations in October 2025 and will update CVE mappings if it discovers additional affected Microsoft products. That phrasing is deliberate: it is precise about what Microsoft has inspected to date, but it is not an exclusionary claim about the entire Microsoft product portfolio.
This article explains what that short MSRC sentence actually means, what other Microsoft artifacts could — technically and practically — be carriers of the same upstream BlueZ/MGMT code, how you should verify whether systems you manage are affected, and which mitigation and prioritization steps are appropriate.
What the CVE actually is (technical summary)
The defect in plain language
- The affected code sits in the Linux Bluetooth stack (BlueZ) MGMT (management) layer that handles control messages between userland and Bluetooth controllers.
- The bug was a locking omission: the mgmt_pending list — a central queue used by MGMT to track outstanding asynchronous operations — was accessed by multiple code paths without a dedicated mutex protecting that list.
- Concurrent access could lead to use‑after‑free or double‑free conditions, which in test harnesses produced KASAN slab‑use‑after‑free errors and kernel crashes. The upstream announcement includes canonical stack traces that show the fault signatures.
Confirming the upstream facts
Two independent, authoritative sources document the vulnerability and the upstream fix: the Linux kernel CVE announce mailing list (the kernel maintainers’ canonical CVE publication) and the National Vulnerability Database (NVD) entry for CVE‑2025‑38117. Use these two sources when mapping the CVE to kernel commits and fixed stable branches.What Microsoft’s MSRC line actually means
Product‑scoped attestation, not exclusivity
The MSRC wording — “Azure Linux includes this open‑source library and is therefore potentially affected” — is an attestation that Microsoft has inspected the Azure Linux build outputs and confirmed the upstream component (the BlueZ / Bluetooth MGMT code) is present in that product family. That makes Azure Linux a confirmed remediation priority. However, that statement does not logically imply that Azure Linux is the only Microsoft product that could include the same code. Microsoft explicitly commits to updating the VEX/CSAF records if additional products are found to be affected.Why vendors publish attestation statements like this
Large vendors ship thousands of distinct binary artifacts, images and kernel builds. Each artifact can be built from different upstream commit ranges and compiled with different kernel CONFIG_* flags. Publishing product‑by‑product machine‑readable attestations is an operationally sensible, phased rollout: start with the product family that’s easiest to inventory (Azure Linux) and expand coverage. In practice, the presence of an upstream file in one product does not prove its absence in others — it demonstrates only that the vendor has checked and attested that specific product.Is Azure Linux the only Microsoft product that includes the BlueZ MGMT code?
Short answer: No — not necessarily. Azure Linux is the only Microsoft product Microsoft has publicly attested (at the time of the advisory) as including the implicated BlueZ/MGMT code. That is an authoritative statement for Azure Linux, but it is not proof of exclusivity: other Microsoft artifacts that ship Linux kernel binaries (or ship userland packages built from Linux distributions) may also include the same upstream component depending on build provenance and kernel configuration. Treat those other artifacts as unverified until you inspect them or Microsoft updates its attestations.Where else to look inside Microsoft’s ecosystem (technical carriers)
The practical places to check — both inside Microsoft‑published artifacts and in environments that use Microsoft tooling — include:- WSL2 kernel images that Microsoft publishes and updates. Microsoft publishes the WSL2 kernel source and build trees; the WSL kernel can include BlueZ/net/bluetooth sources depending on the branch and configuration. If your systems use Microsoft’s published WSL kernel binary, it should be validated. (raw.githubusercontent.com)
- linux‑azure / Azure‑tuned kernels used for some VM SKUs. Microsoft (or its Azure images) can distribute kernels that are built from upstream trees or vendor backports; those kernels need per‑artifact verification.
- Azure Marketplace VM images and curated images. Many Marketplace images are third‑party distributions, but Microsoft publishes or hosts the images and may apply kernel artifacts; check the image's kernel version and configuration.
- Azure Kubernetes Service (AKS) node images and curated container host images. Node host kernels or certain host‑level agents can include vulnerable kernel code.
- Container base images and machine images published by Microsoft that embed distributions; userland packages can include BlueZ or related tooling, although the CVE here is kernel‑side.
- Developer tooling and package managers published by Microsoft (for example, vcpkg or other package artifacts) that might carry or build libraries used by downstream artifacts. The presence of a library in a packaging ecosystem increases the chance it appears in other products or partner solutions.
Confirming exposure: practical verification steps
If you manage systems and want to confirm whether they are affected, follow these artifact‑level checks. The steps below prioritize low‑cost discovery and are suitable for a security operations or platform engineering runbook.1. Identify the kernel binary and version
- Run uname -a (or uname -r) to gather the kernel release string on each host. Record the kernel version and distribution packaging.
- For WSL2, run wsl --status or check the kernel binary Microsoft Update installed for WSL. If you run a custom WSL kernel, treat it as an independent artifact.
2. Check whether Bluetooth/BlueZ kernel sources are present in the running kernel
- Inspect the modules tree for Bluetooth kernel support:
- ls /lib/modules/$(uname -r)/kernel/net/bluetooth
- ls /lib/modules/$(uname -r)/kernel/drivers/bluetooth
- If the net/bluetooth modules are present, check for mgmt_* modules or compiled‑in code that match BlueZ MGMT functionality.
3. Map the running kernel to upstream fixes
- Use the CVE’s upstream commit references (from the linux‑cve‑announce and NVD entries) and compare the commit range or stable branch numbers to your kernel version. When in doubt, ask your distribution or image vendor for the package mapping that shows which upstream commits were included or backported.
4. Inspect source trees when possible (WSL / published kernel repos)
- See whether the public kernel sources Microsoft maintains for WSL include the BlueZ MGMT files. For example, the Microsoft WSL2 kernel source tree includes net/bluetooth/mgmt.c in the linux‑msft‑wsl branches — a practical proof that a Microsoft-published kernel artifact can and does contain BlueZ MGMT sources depending on branch and config. That makes WSL an explicit artifact to verify. (raw.githubusercontent.com)
5. For images (Azure VM images, Marketplace images, container hosts)
- If you run Marketplace or Azure images, check the kernel package version inside the image (dpkg -l kernel-* or rpm -q kernel) and map that to vendor CVE advisories or to the upstream commit mapping in NVD. If you manage many images, use orchestration automation to query package versions at scale.
Prioritization: who to patch first
- First priority: Azure Linux hosts and Microsoft‑published kernels that Microsoft has explicitly attested as including the component. The MSRC attestation is an authoritative signal for Azure Linux. Schedule immediate patching for those images and apply Microsoft’s recommended kernel updates.
- Second priority: WSL2 hosts using Microsoft’s published kernel (if you use the distributed WSL kernel). Confirm the WSL kernel version and apply updates — or instruct users to switch to a patched kernel image. The WSL public kernel repository shows BlueZ mgmt sources in branch trees; that proves WSL kernels are a plausible carrier. (raw.githubusercontent.com)
- Third priority: Azure Marketplace VM images, linux‑azure kernels, AKS node images — these are high‑value cloud artifacts; verify their kernel package versions and apply vendor patches or rebuilds.
- Fourth priority: Developer pipelines, container base images, and any Microsoft‑hosted artifacts that you rely on which might include an older kernel or where BlueZ gets included in userland (less likely to be directly exploitable for this kernel bug, but still worth inventory).
Mitigations and immediate actions
- Apply the vendor/ distro kernel updates that include the upstream fix. The upstream commit is present in stable kernel branches and distributions backported fixes; mapping to specific package versions is available in distribution advisories and NVD. Cross‑reference the package mapping before rolling updates.
- Where immediate kernel updates are not feasible (production constraints), consider:
- Restricting access to local interfaces that can trigger MGMT operations (e.g., limit untrusted accounts’ access to HCI/MGMT control sockets or Netlink controls). Several advisories recommend restricting access to MGMT/Netlink interfaces so untrusted local users cannot submit MGMT commands.
- Using host isolation or workload separation to prevent untrusted workloads from exercising Bluetooth MGMT flows.
- For WSL users: if you use a custom kernel, recompile against a fixed upstream tree or use the patched Microsoft‑distributed kernel once it is updated.
- For large fleets: implement an actionable automation runbook:
- Inventory kernel versions across fleet.
- Query for net/bluetooth artifacts in /lib/modules or kernel config files.
- Cross‑map vulnerable commit ranges to package versions.
- Patch in controlled waves (canary → pilot → broad) with monitoring for stability.
Risks and limitations of Microsoft’s attestation model
Microsoft’s CSAF/VEX rollout — starting with Azure Linux in October 2025 — significantly improves transparency and automation for customers. However, a product‑level attestation is only as useful as the scope it covers: it tells you what Microsoft has inspected and attested for a specific product family. It does not (and cannot practically) assert that no other Microsoft artifact includes the same upstream component. Until a vendor publishes the full set of attestations that cover its entire artifact catalogue, defenders must treat un‑attested artifacts as unknowns and perform artifact‑level verification, especially for kernel‑level issues like this one where the risk is a local kernel crash or denial of service.Two concrete operational risks to be aware of:
- False sense of security: Interpreting Microsoft’s Azure Linux attestation as “only Azure Linux” could lead teams to ignore WSL kernels, Marketplace images, or other Microsoft‑published kernels in their environment.
- Build-time variability: Two kernels compiled from the same upstream tree can include different sets of drivers depending on CONFIG flags and vendor backports. That variability means you must validate the actual artifact you run, not just rely on version numbers alone.
Recommended checklist for security teams
- Patch Azure Linux images first — Microsoft’s attestation makes them a defined, high‑confidence priority.
- For each Microsoft‑provided kernel artifact you use (WSL2 kernel, linux‑azure kernels, curated Marketplace images, AKS host images):
- Record kernel version and package release.
- Compare to upstream commit ranges/fixes in NVD/linux‑cve‑announce.
- Search your environment for Bluetooth device/control socket access and MGMT/Netlink exposure. Harden access to local MGMT interfaces where possible.
- If you operate CI/CD or image build pipelines that consume Microsoft packages or images, add a gating check to scan kernel package versions and module presence.
- When Microsoft publishes CSAF/VEX attestations for additional products, consume the machine‑readable attestations and add them to your automated triage and patch orchestration.
Final assessment and conclusion
- Microsoft’s MSRC advisory is correct and actionable: Azure Linux is a confirmed carrier for the BlueZ MGMT component implicated by CVE‑2025‑38117 and should be patched as a first priority.
- However, Azure Linux is not the only possible Microsoft product that could include the same upstream BlueZ code. Other Microsoft artifacts that ship kernels — notably the WSL2 distributed kernel and any cloud/Marketplace images that use Microsoft‑built kernels or distribution kernels — are plausible carriers and must be verified on an artifact‑by‑artifact basis. The Microsoft WSL2 kernel source tree contains BlueZ MGMT files, which provides concrete proof that Microsoft‑published kernels can include the affected code depending on the branch and config. (raw.githubusercontent.com)
- For defenders the correct operational posture is clear and pragmatic: patch Azure Linux immediately, then inventory and verify other Microsoft‑supplied kernels and images you run, and apply the upstream/distro patches or vendor updates where the kernel build is unpatched. Use the NVD and linux‑cve‑announce entries to map fixed commits to kernel versions and package releases.
Source: MSRC Security Update Guide - Microsoft Security Response Center
