The Linux kernel patch for CVE-2025-39750 fixes a subtle but serious cleanup bug in the ath12k Wi‑Fi driver; Microsoft’s public advisory states that
Azure Linux (the Azure‑tuned Linux distribution)
includes the implicated open‑source code and is therefore potentially affected — but that attestation does not, by itself, prove that no other Microsoft product ships the same vulnerable component. In short: Azure Linux is the only Microsoft product Microsoft has publicly attested so far, but absence of attestation is not proof of absence. Security teams must treat the Azure Linux attestation as authoritative for that product and
verify other Microsoft artifacts on a per‑artifact basis until Microsoft’s phased VEX/CSAF inventory completes.
Background and overview
The reported flaw, tracked as
CVE‑2025‑39750, impacts the
ath12k wireless driver in the Linux kernel — the driver for Qualcomm Atheros Wi‑Fi 7 (ath12k) devices. At a code level, the bug arises when the driver’s RX peer TID setup routine increments a TID counter even when allocation fails; cleanup later iterates based on that counter and may attempt to free or access TID entries that were never allocated. That mismatch can cause
out‑of‑bounds accesses or kernel crashes during error paths, which is the core of the vulnerability.
Microsoft’s public note attached to their CVE entry says that the company has examined and
attested that the Azure Linux distribution “includes this open‑source library and is therefore potentially affected.” Microsoft also published a commitment — through its VEX/CSAF rollout beginning in October 2025 — to publish machine‑readable attestations and to update the CVE/VEX record if additional Microsoft products are later identified as carriers of the same upstream code.
Why this matters: many organizations rely on vendor attestations to triage vulnerability impact across large fleets. When a vendor says “product X includes component Y,” defenders gain an authoritative signal for that product. But vendors also routinely inventory products in phases; a single attestation for one product family does not automatically clear other product families from scope unless the vendor says so explicitly. That distinction is the practical crux of the user question.
What exactly does Microsoft’s attestation mean?
Product‑scoped, not global
Microsoft’s language reflects a
product‑scoped attestation. In other words:
- When Microsoft says Azure Linux includes the code and is potentially affected, that is an affirmative inventory statement for that named product family. Customers running Azure Linux should treat the entry as authoritative and begin triage/patching accordingly.
- When Microsoft says it will update the CVE/VEX entry if other products are identified, that signals a phased inventory approach. Microsoft has not claimed that no other Microsoft artifact includes the code — it has simply not attested any additional Microsoft products yet.
This phrasing is deliberate and aligns with how large vendors typically roll out VEX/CSAF attestations: start small, validate automation and processes, then expand coverage. For security teams, the safe operational interpretation is therefore: treat Azure Linux as confirmed affected, and treat other Microsoft artifacts as “unknown until attested or verified locally.”
Why vendors do this
- Enterprises have hundreds of product images, kernel builds, and marketplace appliances. Each build may use different upstream kernel versions and different build-time CONFIG flags, which determine whether a driver like ath12k is compiled in or as a module.
- Publishing high‑quality, machine‑readable VEX/CSAF declarations at scale requires reliable artifact inventory and SBOM generation. Vendors often pilot with one product family before scaling.
The technical problem: tid bookkeeping in ath12k
To evaluate risk, we must understand the bug mechanics.
- The ath12k driver maintains per‑peer arrays that track TIDs (Transmission Identifiers) used by MAC/aggregation and RX fragment handling.
- During peer/TID setup, the driver increments a tid index as it allocates a new TID entry.
- If allocation fails mid‑loop, the driver’s error path invoked cleanup routines that expect only the successfully allocated TIDs to be freed. Because the tid index was already incremented for the failed allocation, cleanup can attempt to free or access a non‑allocated array entry.
- That results in potential out‑of‑bounds access or freeing of invalid memory — a classical kernel memory‑safety risk. At minimum this can cause crashes (denial of service). Depending on system layout and exploitability of the kernel memory corruption primitive, it could be a stepping stone to privilege escalation or arbitrary code execution — although real‑world exploitation would require a suitable attack surface and triggering conditions.
The published upstream fixes adjust the bookkeeping so that the tid counter correctly reflects only successfully allocated entries before cleanup loops run. They also remove redundant decrements in failure paths to prevent double adjusts that could misalign the cleanup loop.
How serious is this vulnerability in practice?
- Impact type: kernel memory corruption / out‑of‑bounds access, with likely result of system crash (DoS) and theoretical potential for more severe memory corruption exploitation.
- Attack vector: typically requires the attacker to interact with the affected driver. For Wi‑Fi drivers that handle wireless frames, that can mean either:
- Local access to the device (a process on the host that can interact with driver APIs), or
- Over‑the‑air interaction if the device processes received 802.11 frames from nearby wireless transmitters. The latter can make the attack proximity‑based, depending on the driver’s exposure and whether the hardware/firmware passes untrusted frame content to vulnerable paths.
- Remote network exposure: unlike a plain TCP service bug, driver bugs in wireless stacks often require local or proximity adjacency to trigger (a malicious AP or crafted frames from a physical attacker). That doesn’t make them low risk for cloud and mobile contexts: cloud images running on virtualized machines may not have the physical Wi‑Fi device attached, whereas bare‑metal hosts, laptops, and edge devices frequently do.
- Exploitability: Many kernel out‑of‑bounds issues are non‑trivial to weaponize, but they can be exploited with enough sophistication and knowledge of firmware/driver internals. Treat the vulnerability as high‑risk for hosts that expose the affected driver and low to negligible for hardened virtualization hosts that do not present physical Wi‑Fi hardware.
Because of those nuances, determining whether a Microsoft product is actually in scope requires checking whether the product image or kernel build includes the compiled ath12k code (as a module or built‑in) and whether relevant firmware/drivers are present.
Is Azure Linux the only Microsoft product that includes the library?
Short answer: No — it is the only Microsoft product Microsoft has publicly attested to include it
so far, but that does not guarantee exclusivity.
Longer answer (operationally important):
- Azure Linux: Microsoft has explicitly attested that Azure Linux images include the implicated upstream code and are potentially affected. If you operate Azure Linux VMs, treat them as in‑scope and patch according to Microsoft’s guidance or the upstream kernel patches.
- Other Microsoft artifacts: whether they include ath12k depends on artifact‑by‑artifact build choices. Possible Microsoft artifacts that could plausibly include the ath12k driver include:
- WSL2 kernel builds (the Microsoft‑published WSL2 kernel is a full kernel image with configurable drivers). Whether a given WSL kernel includes ath12k depends on the published kernel configuration and build used by Microsoft for that WSL release.
- linux‑azure or azure‑tuned kernel packages used in some VM SKUs — these kernels may be built with multiple drivers enabled and therefore could include ath12k depending on the kernel version and config.
- Azure Marketplace images, partner images, and curated VM images — these are built by Microsoft or third parties; their kernels might include ath12k if the image includes a full distribution kernel with wireless drivers.
- AKS node images, container host images, or specialized virtual appliance images — if they ship a kernel with the wireless stack enabled, they could carry this driver.
- Specialized Microsoft appliances, IoT images, or edge products that embed Linux kernels may also be carriers.
- Because Microsoft has explicitly stated they will update VEX entries if more products are identified, the presence of Azure Linux in the attestation is the first data point, not the final one.
In operational terms: treat Azure Linux as confirmed affected; for everything else —
verify.
How to verify whether your Microsoft artifact is affected (practical checks)
Here are concrete, repeatable checks for different artifact types. Run these on an affected host or image copy — don’t rely on attestation alone.
1) Running Linux VM or physical host (any distro)
Check whether ath12k module or code is present:
- Check loaded modules:
- sudo lsmod | grep -i ath12k
- sudo modinfo ath12k (returns module metadata if present)
- Search installed modules:
- sudo find /lib/modules/$(uname -r) -type f -name 'ath12k'
- sudo grep -R --line-number 'ath12k' /lib/modules/$(uname -r) || true
- Inspect kernel config (if available):
- zgrep 'ATH12K' /proc/config.gz || grep -E 'CONFIG_ATH12K' /boot/config-$(uname -r) || true
- If CONFIG_ATH12K is set to =m or =y, the driver is compiled in or modular.
- Check dmesg for ath12k or firmware loading:
- sudo dmesg | grep -i 'ath12k' || true
If any of the above returns positive results, the kernel includes ath12k and you must treat the host as potentially vulnerable until patched.
2) Azure Linux images (VM images or custom images in Azure)
- If you run Azure Linux images, Microsoft’s attestation already marks them as potentially affected. Still perform image‑level checks:
- Boot the VM and run the checks in section (1).
- For offline image inspection, mount the VHD and search for /lib/modules and /boot/config-* for the chrooted image:
- sudo mkdir /mnt/img && sudo mount -o loop image.vhd /mnt/img
- sudo grep -R --line-number 'ath12k' /mnt/img/lib/modules || true
- sudo zgrep 'CONFIG_ATH12K' /mnt/img/boot/config-* || true
3) Windows Subsystem for Linux (WSL2)
- WSL ships a Microsoft‑built kernel binary; verify the kernel version and config:
- In WSL: uname -r => gets kernel version used by WSL.
- Check for kernel config in /proc/config.gz: zgrep 'ATH12K' /proc/config.gz || true.
- On Windows host, check the WSL kernel package or the published config in Microsoft’s WSL repository if you need to compare the build configuration.
Notes:
- WSL kernels often exclude many hardware drivers that make no sense in a virtualized environment, so ath12k may not be present. But this is a build‑time choice; verify rather than assume.
- Some third‑party WSL kernel builds (community or custom) may include extra drivers; if your environment uses custom WSL kernels, inspect those kernels.
4) Container images, lightweight hosts, and images used in AKS
- Containers do not include the host kernel modules; they use the host kernel. So the relevant question is whether the container host node (VM or bare‑metal) includes ath12k — perform host checks (section 1).
- If an image includes a packaged kernel (e.g., full distro image), inspect /lib/modules and /boot/config-* inside the image as in section (2).
5) Bulk or fleet scanning (script approach)
A minimal script to run on a fleet of Linux hosts:
- uname_r=$(uname -r)
- if lsmod | grep -q ath12k; then echo "$HOST: ath12k loaded"; fi
- if find /lib/modules/$uname_r -name 'ath12k' | grep -q .; then echo "$HOST: ath12k present"; fi
- if zgrep -q 'CONFIG_ATH12K' /proc/config.gz 2>/dev/null; then echo "$HOST: CONFIG_ATH12K set"; fi
For image scans, create a temporary VM or mount image files and run the same checks.
Patching and mitigation guidance
- Prioritize Azure Linux images first. Microsoft’s attestation marks them as "known affected" or "potentially affected"; follow Microsoft’s recommended update path or apply the upstream kernel patches as packaged by your distribution vendor.
- For other Microsoft artifacts (WSL, linux‑azure, marketplace images, AKS nodes, etc.):
- Don’t assume they are unaffected. Run the verification steps above.
- If ath12k is present, apply kernel updates or vendor‑provided patches that include the upstream fix.
- If a patch is not immediately available:
- Consider temporary mitigations:
- Remove or blacklist the module: echo "blacklist ath12k" | sudo tee /etc/modprobe.d/blacklist-ath12k.conf ; update-initramfs -u; reboot.
- Unload module if loaded: sudo modprobe -r ath12k (only possible if not in use).
- Disable Wi‑Fi hardware in host firmware/BIOS on servers where Wi‑Fi is unnecessary.
- Restrict physical proximity and network access controls where feasible.
- For WSL and Windows hosts:
- If Microsoft publishes WSL kernel updates, apply them via the official WSL update process.
- For custom WSL kernels, rebuild the kernel with the upstream fixes applied and deploy to affected endpoints.
- Verify after updates:
- Confirm module is patched or removed: modinfo ath12k should reflect patched version, or module absent.
- Re-run fleet scanning scripts to validate remediation.
How to interpret vendor VEX/CSAF and attestations
- Use the vendor’s VEX/CSAF filings to automate triage. If a vendor marks a product as “Known Affected” or “Fixed,” you can use that signal to prioritize remediation for that product.
- Attestations are product‑level statements. If your environment contains multiple SKUs, images, or custom builds, you must map each artifact to the vendor’s attestation and/or run artifact‑level verification.
- For Microsoft: they began publishing machine‑readable VEX/CSAF attestations in October 2025 and have started with Azure Linux as a pilot. Expect that more products will be attested over time; monitor the vendor’s machine‑readable feeds and CVE records for updates.
Practical recommendations for security teams
- Immediate actions (first 24–72 hours)
- If you operate Azure Linux: treat it as in‑scope. Apply vendor patches or upstream kernel updates as soon as they are available and tested in your environment.
- Inventory Microsoft artifacts in your estate (WSL instances, Azure images, Marketplace images, AKS nodes, edge devices). Map each artifact to a product in Microsoft’s VEX/CSAF feed if possible.
- Run the quick verification checks on hosts and images to detect ath12k presence.
- Short‑term actions (next 1–2 weeks)
- Patch affected hosts and validate remediation scripts.
- For critical hosts where patching is delayed, implement mitigations (module blacklisting, host isolation).
- Update monitoring to detect kernel panics/crashes that might indicate exploitation attempts or triggering conditions.
- Long‑term actions (policy and process improvements)
- Maintain per‑artifact SBOMs or image inventories and integrate vendor VEX/CSAF feeds into your vulnerability management pipeline.
- Automate image scanning for kernel module presence as part of CI/CD gating for image publication.
- For cloud providers and large fleets, maintain a mapping between image SKUs, kernel builds, and VEX attestation states.
Risks and limitations you should be aware of
- Attestation gaps: Vendor attestations are valuable signals but are only as useful as the vendor’s inventory coverage. A product‑level attestation for Azure Linux does not mean other Microsoft kernels are clean.
- Kernel configuration variability: Even the same vendor may ship multiple kernels with different CONFIG_* flags. A kernel built with wireless drivers enabled will include ath12k; one with those drivers disabled will not.
- Container nuance: Containers do not carry their own kernel code; they rely on the host kernel. A container image that includes a packaged kernel is rare, but if present, treat the image as a self‑contained artifact that could include vulnerable code.
- Exploitability nuance: Not all kernel memory errors lead to remote code execution. Many result in crashes. However, mis‑use of a crash (DoS) in production infrastructure can be impactful, and aggressive attackers may attempt complex exploit chains. Treat such kernel bugs with high priority for hosts with exposed attack surfaces.
- Vendor updates: Microsoft’s VEX/CSAF program is evolving; keep watching for updates. Microsoft has pledged to update the CVE/VEX entries if more products are found to include the affected component.
Checklist: What to do right now
- For Azure Linux customers:
- Immediately identify Azure Linux VMs and apply vendor patches or the upstream kernel fixes.
- Confirm remediation via module inspection and reboot verification.
- For WSL users and Windows admins:
- Check WSL kernel version and config. If Microsoft publishes an updated WSL kernel that includes the fix, apply it; for custom WSL kernels, rebuild with the fix.
- For cloud images, AKS nodes, and Marketplace appliances:
- Map image SKUs to vendor attestations. Verify on a sample image whether ath12k exists.
- If present, patch or replace image with a fixed snapshot.
- For large fleets:
- Run automated scanning against deployed hosts to detect modules or kernel configs that indicate presence of ath12k.
- Prioritize remediation for internet‑facing or proximity‑exposed hosts.
- Log and monitor:
- Add signature/alerting for kernel OOPS, panics, or any unusual ath12k dmesg entries.
- Track vendor VEX/CSAF feed for attestation updates — Microsoft has said they will update entries if other products are identified.
Final analysis and conclusion
Microsoft’s public advisory that
Azure Linux includes the implicated open‑source library is an important and authoritative signal for Azure Linux customers: if you run Azure Linux, you must treat CVE‑2025‑39750 as relevant and act accordingly. However, the attestation is product‑scoped and reflects a phased VEX/CSAF rollout that began in October 2025. That means Microsoft has not yet attested other Microsoft product families, but it has not declared them unaffected — it has simply not finished inventory.
Operational security teams should therefore:
- Act immediately to patch Azure Linux instances and verify remediation.
- Verify whether other Microsoft artifacts in their estate (WSL kernels, linux‑azure kernels, AKS nodes, Marketplace images) include ath12k, using the concrete checks and scripts provided above.
- Prioritize assets with exposed wireless hardware or those in physical proximity to untrusted wireless actors, because driver bugs in wireless stacks often require local or proximity triggers.
- Integrate vendor VEX/CSAF feeds into vulnerability management but do not rely solely on them to prove absence of risk; combine attestations with artifact‑level verification and SBOMs.
In short: Azure Linux is the first Microsoft product Microsoft has publicly attested as potentially affected by CVE‑2025‑39750. That attestation is authoritative for Azure Linux and valuable for automated triage, but it is not a global clearance for every Microsoft kernel artifact. Until Microsoft’s phased inventory expands, defenders should verify other Microsoft artifacts directly, apply vendor or upstream kernel patches where needed, and use compensating controls where immediate patching isn’t possible. The good news is that upstream fixes are available and packaged updates are likely; the pragmatic requirement for organizations is to map their artifacts, run the quick checks above, and prioritize remedial action where the driver is present.
Source: MSRC
Security Update Guide - Microsoft Security Response Center