CVE-2025-37787: mv88e6xxx DSA Patch and Azure Linux Exposure

The Linux kernel patch for CVE-2025-37787 fixes a NULL-pointer crash in the Marvell mv88e6xxx Distributed Switch Architecture (DSA) driver by preventing attempts to unregister devlink regions that were never registered, but the practical exposure for enterprises depends on where that driver is shipped and enabled — Microsoft’s public advisory currently maps the CVE to Azure Linux, yet that does not prove Azure Linux is the only Microsoft product that could include the vulnerable code.

Background / Overview​

The vulnerability tracked as CVE-2025-37787 is a kernel-level NULL pointer dereference in the net/dsa/mv88e6xxx driver. During driver unbind the code called devlink_region_destroy() with a NULL pointer for a global devlink region in some chip variants; devlink_region_destroy() is not NULL-tolerant and dereferences the pointer, producing a kernel oops and a crash. The problem stems from conditional registration of certain devlink regions (MV88E6XXX_REGION_STU and MV88E6XXX_REGION_PVT) on some chips: when the region registration is skipped at probe time the driver must not call the corresponding unregister on unbind — the upstream patch simply checks for NULL before unregistering.
This is an availability-impact vulnerability: an attacker with local access (or a buggy driver unbind flow triggered by legitimate operations) can cause a denial-of-service (system crash) by reaching the unbind path when the conditional devlink regions were not created. The assigned CVSSv3 base score in public advisories is mid-range (around 5.5), because the flaw requires local privileges and impacts availability rather than confidentiality or integrity. Several mainstream Linux distributions and vendors have already shipped fixes in their kernel packages.

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What Microsoft said — and what that doesn’t mean​

Microsoft’s public guidance for a range of Linux kernel CVEs has followed a consistent pattern: the company identifies Azure Linux as a known product that includes the affected open-source component and states that it will update the CVE mapping if additional Microsoft products are found to be impacted. That wording is the same text Microsoft has used across multiple kernel CVE entries in its Security Update Guide and CSAF/VEX publications. In other words, Microsoft is explicit about Azure Linux being mapped today — and explicit that the mapping may expand if additional impacts are found.
Important interpretation points for security teams:

• Microsoft’s statement that a CVE is "mapped" to Azure Linux is a product mapping, not a definitive technical proof that other Microsoft-distributed kernels do not contain the code.
• A product mapping typically reflects what Microsoft has verified in its internal inventory and what it is committed to patching now; it is not a guarantee that other Microsoft offerings (for example, other kernels distributed as part of Microsoft products) are unaffected.
• The mapping should be treated as a snapshot: Microsoft will update it if and when additional products are confirmed to ship the vulnerable driver.

Put bluntly: Microsoft’s mapping to Azure Linux is authoritative about Azure Linux, but it is not conclusive evidence that you can safely ignore all other Microsoft-supplied kernels and images until Microsoft explicitly adds them to the CVE mapping.

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Technical context: what mv88e6xxx is and where it lives​

The mv88e6xxx driver implements support for Marvell 88E6xxx family Ethernet switch chips under the kernel’s Distributed Switch Architecture (DSA). The code lives in drivers/net/dsa/mv88e6xxx in upstream Linux and is guarded by the kernel configuration option CONFIG_NET_DSA_MV88E6XXX (or the DSA umbrella options that enable mv88e6xxx as a module). The component is present across many kernel trees and is commonly built as a module on embedded, SoC, and some server kernels that target hardware using Marvell switch silicon.
Why that matters: whether a given Linux kernel actually contains the vulnerable code depends on build-time configuration (is the DSA mv88e6xxx driver built in or built as a module?) and on runtime environment (are those modules shipped/installed and are they loaded). The mere fact that a vendor distributes a kernel does not prove the module is present or loadable — but it does create the possibility.

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Who is known to have fixed this (and who flagged it)​

Within days and weeks of the public disclosure the usual Linux distribution maintainers incorporated the fix into their kernel packages. Security trackers and advisories from Ubuntu, Amazon Linux Advisory Service (ALAS), Snyk, and others list the CVE and confirm that the upstream kernel change avoids unregistering NULL devlink regions, preventing the crash. That cross-vendor coverage is typical for kernel-level fixes and means that most distro-supplied kernels will be patched on their normal update cadence.
Microsoft’s Azure Linux kernel packaging (the linux-azure / azl kernel builds) shows the same family of mv88e6xxx fixes in the azure kernel changelogs and Ubuntu’s linux-azure packages. In practical terms, Azure Linux kernel images used for Azure VM instances have already been mapped and addressed by Microsoft’s advisory process.

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Is Azure Linux the only Microsoft product that could be affected?​

Short answer: No — not necessarily. Microsoft’s current CVE mapping names Azure Linux as the product Microsoft has verified and will patch; however, other Microsoft products and services either ship a Linux kernel or provide Linux VM images or modules — and any of those could include the mv88e6xxx driver depending on how the kernel was built or what modules are present. The presence of the driver is not limited to Azure Linux distributions alone. Key Microsoft-distributed kernels to consider:

• Azure Linux kernel images (explicitly mapped by Microsoft for this CVE).
• The Windows Subsystem for Linux (WSL) kernel: Microsoft ships a Linux kernel to WSL2 users (source and builds are available in the microsoft/WSL2-Linux-Kernel repo), and that kernel is built with a custom configuration and a modules VHD — whether mv88e6xxx is present depends on the WSL kernel configuration and the modules VHD in a specific build. You cannot assume absence without checking the particular shipped kernel version and module set.
• Azure Marketplace and publisher VM images, AKS node images, and other Microsoft-curated images can use various base kernels (including Ubuntu’s linux-azure or vendor supplied kernels) — those images may therefore contain mv88e6xxx if the kernel config includes it.
• Any Microsoft-managed appliance or service that embeds a Linux kernel (appliance VM images, container host images, virtual appliances) could be affected if the kernel includes the driver. Microsoft’s mapping will be updated if their product inventory reveals additional affected items.

Put another way: Microsoft’s public statement names Azure Linux because that is where the company has definitively identified the vulnerable library in its product inventory. It is the authoritative mapping for Azure Linux, but it is not a technical proof that no other Microsoft product contains the code. Administrators must treat other Microsoft-delivered kernels as potentially vulnerable until they verify otherwise.

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How to verify exposure in your Microsoft environment​

Do not assume “not listed = not affected.” Inventory and verification are straightforward and must be treated as routine hygiene. Here are actionable checks and detection steps you can run across the environments you manage.

Quick checks on Linux hosts (VMs, on-prem, appliances)​

• Check whether mv88e6xxx is present in the modules tree:
• grep -R "mv88e6xxx" /lib/modules/$(uname -r) || lsmod | grep mv88e6xxx
• Attempt to query the module (shows the module if installed as a kernel module):
• sudo modinfo mv88e6xxx
• Check kernel config for the option (works if /proc/config.gz or /boot/config-$(uname -r) is available):
• zgrep CONFIG_NET_DSA_MV88E6XXX /proc/config.gz || grep CONFIG_NET_DSA_MV88E6XXX /boot/config-$(uname -r)
• If you find the module present, check whether vendor packages backport the fix (compare package versions to distro advisories). Many distros list fixed kernel package versions in their CVE pages.

WSL-specific checks (Windows hosts running WSL2)​

• Determine the running WSL kernel version:
• In a WSL shell: uname -r
• On Windows: wsl --status (shows WSL kernel version and whether a custom kernel is configured)
• If your WSL uses the Microsoft-supplied kernel (default), note the kernel version and check the WSL modules VHD for the presence of the mv88e6xxx module. If you use a custom kernel (via .wslconfig), inspect your custom kernel configuration and module set.
• If the Microsoft WSL kernel version corresponds to a kernel branch where mv88e6xxx is present and built into the module set, treat WSL as potentially exposed until you confirm the module absence or that Microsoft has patched that exact WSL kernel build. Microsoft’s kernel repository and the WSL project page are the right places to start that verification.

Azure-specific checks (VMs, AKS nodes, Marketplace images)​

• Identify which kernel package is installed on your Azure VMs. In Microsoft’s CSAF mappings and Azure kernel product names you’ll often see kernel identifiers like “azl3 kernel 6.6.x” or explicit "Azure Linux" kernel package names; those product names are what Microsoft maps to CVEs in their VEX/CSAF outputs. Use the distro package manager to check installed kernel package details and compare against the vendor advisory.
• For AKS or other managed node pools, verify the node image and node OS image build and whether Microsoft has issued a security bulletin for the image. If nodes are based on Azure Linux or a patched distro, follow the vendor update guidance.

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Mitigations and remediation options​

If you identify exposure, here are practical, prioritized remediation options:

• Apply vendor kernel updates immediately. This is the recommended fix: install the patched kernel package from your distribution or from Microsoft for Azure Linux images. Distribution advisories (Ubuntu, Amazon, SLES, etc.) list the patched kernel versions and should be followed.
• Where patching isn’t immediately possible, temporarily mitigate by blacklisting or preventing the driver from being loaded:
• Create a blacklist entry in /etc/modprobe.d/ to prevent mv88e6xxx from loading.
• Remove the module from the running kernel (rmmod) only if it is not in use and doing so won’t disrupt operations.
• For WSL, switch to a custom kernel build that omits the driver or apply an updated WSL kernel release from Microsoft once one is published that includes the fix. If you rely on WSL in developer environments, coordinate distribution of a safe WSL kernel through internal channels.
• For Azure-managed images, follow Microsoft’s recommended upgrade path for Azure Linux and for Marketplace image updates; Microsoft’s CSAF/VEX feeds provide machine-readable mapping and remediation data for Azure Linux kernel packages.

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Risk assessment and practical exposure scenarios​

Who actually runs mv88e6xxx code in production? The realistic exposure surface is narrower than "all Linux machines" because mv88e6xxx targets Marvell 88E6xxx switch silicon. That hardware is most common in embedded network equipment, switches on systems with onboard Marvell switches, and certain SoC-based appliances. For cloud VM images running on generic server NICs (Intel, Broadcom, Mellanox), the mv88e6xxx driver may simply never be loaded. That said:

• Azure Linux images used on Azure VMs can include the driver in the kernel package; Microsoft has already mapped Azure Linux to this family of kernel CVEs and will ship updates as needed.
• WSL and custom kernels: many WSL kernels are intentionally trimmed to remove unnecessary drivers, but the exact kernel build and modules shipped with a given WSL release determine exposure. Microsoft’s WSL kernel tree is public; the only reliable way to know is to inspect the specific WSL kernel build or the modules VHD for a running system.
• Enterprise network appliances / on-prem hardware that include Marvell switch chips are the highest-risk class of hosts; on such systems a careful vendor-specific patching plan is essential because those kernels are often vendor-supplied or heavily customized.

In short: the practical risk is concentrated on systems that either run the kernel modules for Marvell DSA switches or run kernels built with those drivers enabled — and those systems are precisely the ones administrators must inventory and patch.

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Critical analysis of Microsoft’s messaging and responsibilities​

Microsoft has taken steps to improve transparency for Linux components it distributes: the company publishes CSAF/VEX files and maps open-source kernel CVEs to Azure Linux product identifiers where appropriate. That’s a meaningful improvement for customers who consume Azure Linux images, because it provides a clear lineage and a patching path.
However, this model has two notable operational risks for enterprise customers:

• Overreliance risk: Customers who interpret "Azure Linux is the only Microsoft product that includes this library" as "no other Microsoft product can be affected" are at risk. Microsoft’s CVE mapping covers what they have audited and committed to remediate; it is not an exhaustive technical guarantee about all products, especially when Microsoft distributes multiple kernels and VM images across Azure, WSL, and other channels. The company explicitly leaves room to update the mapping, but customers must actively verify other Microsoft-provided kernel images in their environment.
• Inventory and visibility burden: The root cause of the gap is inventory complexity. Large organizations often consume kernels and images from multiple sources: vendor-supplied kernels on appliances, Microsoft-supplied WSL kernels for developer machines, Azure-supplied VM images for cloud workloads, and custom kernels for specialized workloads. Each of those requires a separate verification step. Microsoft’s CSAF outputs make verification easier for Azure Linux, but they do not remove the need for customers to inspect WSL kernels, Marketplace images, and node images for Kubernetes services.

The pragmatic conclusion: Microsoft’s approach is responsible and improves transparency, but it transfers the task of verification and inventory to administrators. That is an acceptable trade — provided organizations act on it.

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Recommended checklist for administrators (prioritized)​

• Inventory all Microsoft-distributed kernels in your environment:
• Azure Linux VMs, Marketplace images, AKS node pools.
• WSL installations (corporate developer laptops and CI agents).
• Any Microsoft-supplied appliance or image used by your teams.
• For each kernel/image, verify whether mv88e6xxx is present:
• Use the detection commands in the “How to verify” section above.
• Patch immediately where the module exists and vendor patches are available:
• For Azure Linux, apply the vendor-supplied azure kernel update.
• For distro-based VMs, apply the distro kernel update (Ubuntu, Debian, RHEL variants).
• If you cannot patch immediately, mitigate:
• Blacklist the module or prevent it from loading in the environment.
• For WSL, instruct developers to use a patched or custom kernel until Microsoft releases a patched WSL kernel.
• Monitor Microsoft’s CSAF/VEX outputs and MSRC advisories for changes:
• Microsoft has committed to publishing machine-readable CSAF files; use those feeds to automate inventory comparisons and AV/patching workflows.
• Document and communicate internally:
• Ensure developer teams, cloud operations, and security operations have a shared inventory of which Windows hosts run WSL and which Azure VMs use Azure Linux or other Microsoft-curated images.

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Conclusion​

CVE-2025-37787 is a straightforward kernel NULL-pointer crash in the mv88e6xxx DSA driver that affects availability. Microsoft’s public mapping identifies Azure Linux as a product that contains the vulnerable open-source code and is being tracked and remediated; but Microsoft’s statement is intentionally scoped and does not prove other Microsoft-supplied kernels (WSL2 kernels, Marketplace images, AKS node images, or appliance images) are unaffected. Administrators must therefore verify the presence of the mv88e6xxx driver in their Microsoft-distributed kernels and apply kernel updates or mitigations where the module exists.
This approach — treat Microsoft’s mapping as a definitive statement about Azure Linux while treating other Microsoft products as potentially vulnerable until verified — is the safest posture. Inventory, detection, and timely patching remain the right operational responses.

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Source: MSRC Security Update Guide - Microsoft Security Response Center