The Linux kernel vulnerability tracked as CVE‑2025‑38129 is a use‑after‑free in the page_pool subsystem (page_pool_recycle_in_ring) that can cause kernel memory corruption or panics, and Microsoft’s public advisory naming Azure Linux as a product that “includes this open‑source library and is therefore potentially affected” is an authoritative product‑level attestation for Azure Linux — but it is not a technical guarantee that
no other Microsoft product can include the same vulnerable code. s://nvd.nist.gov/vuln/detail/CVE-2025-38129)
Background / Overview
CVE‑2025‑38129 was reported by syzbot and documented by the Linux kernel CVE team as a classic use‑after‑free in the page_pool recycling path. The failure happens when the page pool is recycled and, under a race condition, the pool structure can be freed while another thread is still executing code that accesses data in the pool, producing a KASAN‑detected slab use‑after‑free. The kernel project assigned the fix to multiple stable branches and provided specific commits that close the race.
Several downstream vendors and trackers mirrored the upstream announcement and issued advisories or status entries for their distributions. For example, Amazon Linux and Debian trackers list the CVE and map fixed/affected package versions for the kernels they ship. Those distribution entries are useful cross‑checks for operators who need to know whether a particular kernel release in their environment is affected.
Microsoft’s Security Response Center (MSRC) published a short product‑mapping statement for the CVE that reads, in essence, “Azure Linux includes this open‑source library and is therefore potentially affected by this vulnerability.” That sentence is part of Microsoft’s phased rollout of machine‑retations (announced October 2025) and indicates Microsoft has inspected the Azure Linux distribution artifacts and found the implicated upstream code there. The MSRC phrasing and the VEX rollout are explicitly product‑scoped: they tell customers which named Microsoft product(s) have been inventoried and found to include the upstream component.
What the vulnerability is — technical anatomy
The bug in plain terms
- Where: net/core/page_pool.c, function page_pool_recycle_in_ring.
- Root cause: insufficient synchronization around the producer lock when recycling the last page in the ring; the pool structure can be freed by a concurrent destructor while another CPU is still using ring state, producing a use‑after‑free.
- Observable symptom: KASAN reports like “slab‑use‑after‑free in lock_release …” followed by a call trace that includes page_pool_recycle_in_ring and lock_release.
Upstream maintainers addressed the defect by inserting an appropriate producer‑lock barrier in page_pool_release and related code paths so that the pool cannot be destroyed while other CPUs are still recycling ring entries. The linux‑cve‑announce post documents the exact fixes and points to the stable commit IDs that implement the corrections. Those commits are the canonical references for vendors that either update kernels or backport patches to stable branches.
Practical impact profile
- Primary impact: availability and integrity of kernel memory — the defect can yield kernel oops, panic, or memory corruption that disrupts hosted services.
- Attack vector: local or guest (requires the ability to interact with kernel networking paths or the capacity to cause the recycling scenario). On multi‑tenant cloud hosts, the attack surface may be larger (guest → host interactions), so stability risks translate into higher operational urgency.
- Exploitability: it is a kernel memory corruption primitive (UAF) which is concerning; while local access is typically required, UAFs at kernel privilege level can be combined with other primitives for escalation in specific cases. Existing public triage classifies the issue as important/serious and assigns CVSS scores in the 7.x range for some vendor trackers. (wiz.io)
What Microsoft’s MSRC statement actually means
Attestation versus exclusivity
When MSRC states a named product “includes” the implicated code, that is an explicit inventory attestation for that product family: Microsoft checked the Azure Linux build outputs (images, kernel packages, or both) and found the upstream page_pool code that maps to the CVE. That makes Azure Linux a
confirmed carrier until Microsoft publishes a “fixed” or “not affected” attestation for that product. Treat MSRC’s attestation as authoritative for Azure Linux.
Critically, however, that attestation is
product‑scoped, not an exhaustive statement about Microsoft’s entire portfolio. Microsoft’s public line — including the phrase that the company will update CVE records if additional Microsoft products are identified — reflects a phased inventory process. Large vendors typically publish product‑level attestations as each product’s artifact inventory completes; absence of an attestation for Product X is
not proof that Product X is free of the code, it is simply an absence of attestation. Multiple independent analyses have repeated exactly this point: Azure Linux is the only Microsoft product Microsoft has publicly attested for this CVE so far, but other Microsoft artifacts that ship Linux kernels or kernel‑based images could also include the code until inventoried and attested.
Why Microsoft started with Azure Linux
Azure Linux (the distribution Microsoft maintains for some Azure images) is a manageable, high‑value target for an initial VEX/CSAF rollout: it is a clear, bounded product family and many Azure customers run its images. Microsoft intentionally prioritized it to deliver deterministic, machine‑readable attestations quickly and to provide immediate operational guidance for users who run Azure Linux images. That operational choice speeds automation for Azure customers while inventory for other product families completes. The key takeaway: Microsoft has given Azure Linux early, authoritative coverage — but that incremental coverage does not equate to exhaustive scanning of every Microsoft image, kernel build, or container artifact.
Is Azure Linux the only Microsoft product that includes the implicated code?
Short answer: No — Azure Linux is the only Microsoft product Microsoft has publicly attested so far to include the vulnerable upstream code for CVE‑2025‑38129, but other Microsoft artifacts
could include the same vulnerable page_pool code until they are inventoried or attested. The attestation is definitive for Azure Linux, but the absence of attestations for other products does not prove absence of the code.
Which Microsoft artifacts are plausible carriers?
Any Microsoft product that ships or runs a Linux kernel binary built from a pre‑fix upstream snapshot that included the vulnerable commit range can be a carrier. Examples to check include (but are not limited to):
- Windows Subsystem for Linux (WSL2) kernels that Microsoft distributes to Windows clients.
- Azure VM kernel images and linux‑azure kernel packages used in some Azure VM SKUs.
- Azure Marketplace VM images or partner appliances that embed a Linux kernel.
- AKS node images or curated container host images Microsoft supplies.
- Any Microsoft management or telemetry agents that contain bundled kernel modules or kernel‑based tooling.
Each of these artifacts is built from potentially different kernel snapshots and configurations; inclusion depends on the kernel version, the build configuration (whether net/core/page_pool is compiled in), and any vendor backports. Until Microsoft publishes a product‑level VEX/CSAF attestation declaring a product
Not Affected or
Fixed, operators should treat those artifacts as
unverified and run artifact‑level discovery and scanning.
How to verify whether a specific Microsoft artifact in your estate is affected
Below are pragmatic, evidence‑based steps you can run immediately. These steps are designed to determine whether a kernel binary includes the vulnerable page_pool code or whether a given image needs patching.
- Identify the kernel binary or image you run (for VMs, WSL kernels, containers or appliances). Record exact image tags, kernel package versions, and build metadata.
- Check kernel version and build info:
- On a running Linux guest: uname -a; check /proc/version and dmesg for build strings.
- On WSL2: use wsl --status and inside the WSL instance run uname -a; WSL kernels Microsoft distributes often include version/build metadata you can validate.
- Check for the fixed commits or affected commit range:
- The upstream advisory lists the introducing commit and the stable fixes (the linux‑cve‑announce entry gives the commit IDs and the stable kernel snapshots where the fix landed). Compare your kernel’s git commit tag or version against the affected/fixed versions documented by the kernel CVE team.
- Inspect kernel symbol table or strings if you cannot get build metadata:
- Use tools (strings vmlinux | grep page_pool_recycle_in_ring) on the kernel image to search for function names when symbol information is included. If the symbol is present, that indicates the code path exists in that build.
- Check kernel configuration:
- If /proc/config.gz is available, zcat /proc/config.gz | grep PAGE_POOL (or similar CONFIG_PAGE_POOL_STATS) to see compile‑time options that indicate whether page*pool code was built. If the code is not present (CONFIG** disabled), the artifact is not affected by this specific path.
- If you maintain images centrally (Marketplace images, container images supplied by Microsoft), request the Microsoft VEX/CSAF attestation for that product or ask the publisher for a kernel‑etadata to confirm presence/absence.
These steps combine static verification and runtime inspection. When in doubt, treat an unverified image as
potentially affected for prioritization while you complete verification and remediation.
Patching and mitigation guidance
- Patch priority: any Azure Linux images in production should be patched per Microsoft’s updates immediately, because MSRC has attested those images as potentially affected. Apply vendor kernel updates as they become available and follow Microsoft’s published remediation guidance for Azure Linux.
- Upstream recommendation: update kernels to the latest stable release that includes the page_pool fixes or apply the exact stable commits referenced by the kernel CVE team if you need to backport changes into a long‑lived supported kernel tree. The linux‑cve‑announce entry lists the stable commits that implement the fix.
- Short‑term hardening: minimize exposure of multi‑tenant hosts to untrusted local users/guests and restrict capabilities that allow unprivileged users to trigger kernel networking paths that may exercise page_pool recycling. This is defensive — it reduces blast radius while patching proceeds.
- Image rebuilds: for container or appliance images that embed kernels, rebuild images using patched kernel packages and retire old images from registries and marketplaces.
- WSL2 and clienor Microsoft’s WSL release notes and Windows Update channels for patched WSL2 kernels; apply Windows updates that include WSL kernel refreshes where applicable.
Vendor trackers and distribution advisories (Debian, Oracle, Amazon Linux) document the vendor‑specific package updates and statuses; consult those advisories to map the upstream commit to distribution package names and fixed versions in your ecosystems.
Operational recommendations for Microsoft customers and service operators
- Prioritize Azure Linux workloads for immediate remediation because Microsoft has attested those images as potentially affected; the attestation makes Azure Linux the canonical, actionable priority.
- Simultaneously perfocovery across other Microsoft images and kernels in your estate: WSL2 kernels on developer machines, Azure Marketplace images, AKS nodes, and any Microsoft‑published VM or container host images. Do not assume “no attestation = safe.”
- Use image scanning and SBOM tooling to detect vulnerable kernel versions or the presence of the implicated page_pool code in images you run. Where possible, automate the mapping of kernel versions to the upstream commit range that introduced/fixed the bug.
- Request VEX/CSAF attestations from Microsoft for specific product families you operate (if those attestations are not yet published). Microsoft has said it will expand its product‑level mappings and update CVE pages when additional products are found to ship the same component; ask your Microsoft support or account teams to accelerate attestation requests for high‑value artifacts.
- If you run multi‑tenant hosts or cloud images that may be co‑located with untrusted workloads, increase monitoring for kernel oops/panics and instrument rescue processes (automated failover, graceful restart, memory‑corruption alarms) until you confirm all images are patched.
Detection and telemetry: what to look for
- Kernel oops/panic messages that contain KASAN reports and call traces referencing lock_release, page_pool_recycle_in_ring, or net/core/page_pool.c.
- Elevated rates of kernel crashes on networking heavy‑I/O paths that exercise page pool recycling (NAPI paths, skb recycling).
- Unexpected KASAN output in labs or fuzzing runs that replicate the syzbot reproduction environment (syzbot is the origin of the initial report).
- Correlate kernel crash logs with recent image changes, container host kernel upgrades/downgrades, and recent backport activity.
The upstream advisories and distribution trackers include example call traces; instrument your central logging to capture those tracen repeated occurrences.
Risks, strengths, and open questions
Strengths and positive signals
- Upstream responsiveness: kernel maintainers assigned a CVE, published fixes across stable branches, and documented exact commits. That makes vendor patching straightforward: vendors can eitherble kernels or cherry‑pick the stable commits.
- Vendor coordination: multiple distributions tracked and remediated the issue (Debian, Amazon Linux, Oracle, etc.), giving operators several independent references for mapping fixes to vendor package names.
- Microsoft transparency for Azure Linux: MSRC’s product‑level attestation and the CSAF/VEX rollout provide deterministic signals for Azure Linux customers and remove ambiguity for that product family.
Remaining risks and caveats
- Inventory gap: Microsoft has publicly attested Azure Linux but is still phasing Vother products. That means a residual verification burden for defenders who run other Microsoft images or artifacts — those artifacts must be validated independently until Microsoft publishes attestations. Treat lack of an attestation as “unverified,” not “safe.”
- Heterogeneous artifact landscape: Microsoft publishes many kernel‑based artifacts with varying build pipelines (WSL2, linux‑azure kernels, Marketplace images, AKS node images). Each artifact requires its own verification against the fixed commit range; blanket assumptions are unsafe.
- Complexity of backports: vendors sometimes backport fixes into older stable kernels instead of upgrading to a newer kernel version. That makes automated matching by kernel version ineffective unless you also verify specific backport commits or vendor advisory mappings.
Unverifiable claims to watch for
-icrosoft product other than Azure Linux contains the code” is unverifiable without per‑artifact attestations. Until Microsttestations or you independently verify specific artifacts, that exclusivity claim is uncertain and should be treated cautiously.
Conclusion
CVE‑2025‑38129 is a concrete, upstream kernel use‑after‑free in the page_pool recycling path that the kernel community fixed and distributed across stable trees. Microsoft’s MSRC entry correctly and helpfully attests that Azure Linux includes the implicated code and is therefore potentially affected; that attestation gives Azure Linux customers a precise, actionable priority for remediation. However, that attestation is product‑scoped and not a blanket statement about all Microsoft artifacts. Any Microsoft product that ships or runs a Linux kernel built from an upstream snapshot that predates the upstream fixes — including WSL2 kernels, Azure VM kernels, Marketplace images, and AKS nodes — can be a plausible carrier until the product is inventoried and attested as
Not Affected or
Fixed.
Actionable priorities for operators:
- Immediately apply Microsoft’s Azure Linux patches if you run Azure Linux images.
- Run artifact‑level verification (kernel version, config, symbol checks) for other Microsoft artifacts you operate and treat un‑attested artifacts as potentially affected until verified.
- Automate image scanning and SBOM / VEX ingestion so that when Microsoft publishes additional attestations you can rapidly reconcile and remediate.
- Monitor kernel oops/panic telemetry for the page_pool call traces described by the kernel advisory and escalate any reproduction to vendor support.
Microsoft’s product attestation for Azure Linux is valuable and correct — it gives Azure Linux customers a clear, prioritized remediation path — but it does not eliminate the verification work operators must do across the rest of their Microsoft‑supplied artifacts. Treat Microsoft’s VEX/CSAF outputs as the authoritative source for attested products, and use the kernel CVE team’s commit list and vendor advisories to guide patching and verification across your environment.
Source: MSRC
Security Update Guide - Microsoft Security Response Center