Azure Linux Attestation for CVE-2025-37807: What You Need to Know

Microsoft’s short, pointed wording on CVE-2025-37807 — “Azure Linux includes this open‑source library and is therefore potentially affected” — is accurate for the product Microsoft has inspected and is useful for customers running those images, but it should not be read as a blanket guarantee that no other Microsoft product could ever carry the same vulnerable component.

Background​

CVE-2025-37807 is an upstream Linux‑kernel change described as “bpf: Fix kmemleak warning for percpu hashmap.” At a technical level the fix addresses kernel instrumentation and lifetime reporting (kmemleak warnings) related to percpu hashmaps used by BPF subsystems; these sorts of fixes typically correct correctness and reliability issues in kernel bookkeeping rather than introducing new remote code execution primitives. Multiple downstream trackers and distribution advisories treat these kernel fixes as stability/availability or diagnostic‑noise fixes and have pushed backports and updates into stable kernel branches.
Microsoft’s MSRC advisory maps that upstream component into a Microsoft product context and explicitly calls out Azure Linux as the Microsoft product the company has validated as including the open‑source component and therefore being “potentially affected.” Microsoft also committed to publish machine‑readable CSAF/VEX attestations beginning October 2025 and to update the CVE entry if additional Microsoft products are discovered to ship the same upstream code. That procedural language is deliberate and important for operators parsing vendor statements.

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What Microsoft actually said — and how to read it​

Microsoft’s wording follows a now-common, phased approach to supply‑chain transparency:

• Microsoft validates the presence of an upstream component in a specific product family and publishes a product‑scoped attestation (CSAF/VEX) for that family.
• That attestation is authoritative for the named product(s) (here, Azure Linux).
• Microsoft will expand the attestation and update the CVE if additional Microsoft products are later identified as carriers of the same component.

In short: Azure Linux is the only Microsoft product Microsoft has publicly attested as including the component for CVE‑2025‑37807 at the time of the advisory, and Microsoft will update the record if their internal inventories flag other Microsoft SKUs. The statement is an inventory attestation, not a global negative for every Microsoft artifact.
This means two practical realities for operators:

• If you run Azure Linux images, treat Microsoft’s VEX/CSAF attestation as the authoritative, machine‑readable input for triage and remediation for those images. Prioritize patching and image updates according to Microsoft’s guidance.
• If you run other Microsoft‑published images, kernels, or artifacts (WSL kernels, Marketplace images, linux‑azure kernel packages, CBL‑Mariner artifacts, container base images), do not assume they are unaffected. Absence of an attestation is not proof of absence; these artifacts must be verified by per‑artifact inventory and/or by waiting for Microsoft to expand its VEX mapping.

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Technical context: bpf, kmemleak and percpu hashmaps — what this CVE means in practice​

To make good risk decisions you need to translate the short CVE line into operational impact:

• BPF (Berkeley Packet Filter / eBPF): a powerful in‑kernel virtual machine used for instrumentation, networking, tracing and programmable datapath logic. eBPF capability is commonly present on modern distributions and most cloud images expose it to guests for observability and networking use cases.
• percpu hashmap: a kernel data structure optimized for per‑CPU storage/scalability; used by highly concurrent subsystems to avoid cacheline contention.
• kmemleak: a kernel diagnostic facility that attempts to detect memory leaks; kmemleak warnings surface when kernel memory that should be freed is still reachable or otherwise suspicious.

A change fixing a kmemleak warning associated with a percpu hashmap used by BPF is very often a correctness/diagnostic fix. The immediate operational symptom is typically kernel logs showing kmemleak warnings, potentially followed by more severe stability anomalies under adversarial or pathological workloads. The commonly recommended response pattern is to apply the kernel updates from your vendor and, where necessary, validate by running representative eBPF workloads or BPF selftests to ensure the messages and warnings no longer appear.
Crucially, the attack vector for this class of fix is usually local — an actor who can load BPF programs (unprivileged or privileged depending on system settings) may trigger the conditions that surface the warning or cause instability. That makes the risk profile one of availability and reliability more than a remote code‑execution escalation, although kernel stability issues can be weaponized in complex, chained attacks in some environments.

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Is Azure Linux the only Microsoft product that includes the library and is therefore potentially affected?​

Short answer: No — not necessarily. Azure Linux is the only Microsoft product Microsoft has publicly attested as including the upstream component for CVE‑2025‑37807 at the time they published the advisory, and that attestation is authoritative for Azure Linux images. However, other Microsoft artifacts could also include the same upstream code depending on how they were built and packaged; Microsoft’s attestation model is phased and product‑scoped and will be expanded if additional artifacts are discovered.
Expanded explanation:

• Vendors ship many independent artifacts that compile or package the Linux kernel in different ways — kernel configuration, built‑in modules versus modules, static linking and build pipelines all matter. Microsoft produces multiple Linux‑related artifacts (Azure Linux images, linux‑azure packages, Marketplace images, AKS node images, WSL2 kernel binaries, and historically CBL‑Mariner‑based images). Each is an independent build that may or may not include the vulnerable percpu hashmap path. Microsoft’s single‑product attestation does not automatically cover those other artifacts.
• Some Microsoft artifacts are explicitly Linux kernels that Microsoft maintains (for example, the WSL2 kernel repo is a Microsoft‑maintained kernel tree). Those repositories may include substantial upstream code trees (drivers, networking, BPF areas), so whether a WSL kernel is vulnerable depends on its kernel version and the commits it includes — you have to check the WSL kernel build/version to be certain.
• Marketplace VM images, partner appliances, and container base images hosted under Microsoft’s platforms can embed older or third‑party components that evade a central product attestation until explicitly inventoried. Those images remain plausible carriers until inspected and remediated.

So while the MSRC line gives a clear remediation path for Azure Linux users, it does not prove that other Microsoft products are unaffected. Treat the VEX/CSAF attestation as a prioritized automation signal for Azure Linux only, and verify other Microsoft artifacts independently.

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What verification steps security and ops teams should take now​

• Act immediately if you run Azure Linux
• Consume Microsoft’s VEX/CSAF attestation for CVE‑2025‑37807 and apply the Microsoft-provided image or kernel update for Azure Linux as directed. This is the highest‑priority, lowest‑ambiguity remediation for customers who run those images.
• Inventory all Microsoft‑supplied images and kernels in your estate
• Enumerate Azure VM images, Marketplace images, AKS node images, container base images, WSL kernels on developer hosts, and any custom images built from Microsoft bases. Each artifact must be inspected because a single VEX attestation covering Azure Linux does not imply all Microsoft artifacts are covered.
• Use automated SBOM and image‑scanning/SCA tools
• Scan images and binaries for the kernel versions and upstream commit IDs that include or predate the upstream fix; for static or embedded builds, rely on binary scanning and SBOM layer inspection. If you find embedded stacks or statically linked binaries built with older toolchains, schedule rebuilds with patched components.
• Apply short‑term mitigations where patching will be delayed
• Consider tightening BPF usage policies: set kernel.unprivileged_bpf_disabled = 1 for systems that do not require unprivileged BPF, and audit CAP_BPF/CAP_SYS_ADMIN grants for processes and containers. Those mitigations reduce exposure to local attackers or untrusted workloads while you complete patch rollouts.
• Monitor kernel telemetry and BPF signals
• Add alerts for kmemleak warnings, BPF verifier warnings, OOPS messages, or other kernel warnings that match the CVE symptoms. Validate remediations by reproducing representative eBPF loads or running BPF selftests on patched kernels.
• If you operate multi‑tenant hosts, prioritize host kernel patching
• Stability faults in the kernel on a host can affect many tenants; prioritize host patching on shared infrastructure and consider isolating or rehosting high‑risk tenants while you patch.

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Cross‑checking and corroboration — how to confirm presence/absence in other Microsoft products​

Reliable confirmation that a Microsoft artifact contains the affected code requires either:

• A Microsoft VEX/CSAF attestation explicitly naming that product or SKU as “Known Affected” (or “Fixed”), or
• Direct artifact inspection by you (or your vendor) verifying kernel version, commit IDs, or binary content.

Vendor attestations are authoritative for the products they cover, but they are incremental: vendors often begin with a single family and expand coverage as inventories complete. Independent distribution trackers (NVD, Debian/Ubuntu/SUSE security advisories) and upstream kernel commit histories are helpful for confirming the technical facts (affected kernel paths, fixed commits and fixed releases), but they do not answer the per‑artifact Microsoft question unless Microsoft exposes that mapping via VEX or you examine the artifact yourself. Treat the Microsoft attestation as a reliable, prioritized signal for Azure Linux while using upstream and distributor trackers to confirm the technical fix and validate vendor backports.

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Notable strengths of Microsoft’s approach — and the remaining risks​

Strengths

• Machine‑readable VEX/CSAF attestations give enterprises a deterministic, automatable input for triage, SLAs and patch orchestration. Starting with Azure Linux provides an immediate, high‑value signal for cloud customers.
• Explicit commitment to update CVE/VEX records if additional Microsoft products are found to include the component provides transparency and a procedural promise to expand coverage as inventories mature.
• The attestation model reduces uncertainty for Azure Linux customers and speeds remediation workflows for the assets it names.

Risks and limitations

• Phased coverage leads to partial visibility. Large vendors ship thousands of artifacts; a single product attestation does not guarantee global coverage. Operators who mistake product-specific VEX entries for universal vendor safety may leave other artifacts unverified and vulnerable.
• Long‑tail images and marketplace appliances may embed older kernel builds and avoid central inventory checks; these remain a plausible source of exposure until scanned and validated.
• Static linking and bundled toolchains can hide vulnerable components inside binaries; package‑level updates are not sufficient to remediate statically compiled artifacts without rebuilds.

Operational takeaway: Microsoft’s transparency program materially improves clarity for the artifacts it covers (start with Azure Linux), but it does not eliminate the operator’s responsibility to inventory and validate all Microsoft artifacts they actually run.

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Practical checklists (operator playbook)​

• Immediate (Azure Linux):
• Subscribe to the MSRC VEX/CSAF feed for CVE‑2025‑37807 and apply the Microsoft image or kernel update for Azure Linux.
• Validate post‑patch by running BPF selftests and reviewing kernel logs to ensure the kmemleak warnings have disappeared.
• Short term (all Microsoft artifacts you run):
• Enumerate: VM images, AKS node images, Marketplace images, WSL kernels, container base images, Azure Marketplace appliances.
• Scan: SBOMs, SCA, and image layer analysis for kernel versions, upstream commit IDs, or embedded static binaries built with affected toolchains.
• Compensate while patching:
• Tighten unprivileged BPF restrictions (kernel.unprivileged_bpf_disabled), audit capabilities, and limit who can load BPF programs.
• Temporarily isolate high‑risk hosts or rehost critical workloads to patched hosts where feasible.
• Long term:
• Integrate vendor VEX/CSAF feeds into your patch orchestration and SBOM pipelines so product‑scoped attestations automatically drive triage priorities.
• Validate Marketplace and partner images before accepting them into production pipelines; require SBOMs and rebuilds for vendor‑supplied appliances as part of intake.

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When to expect Microsoft to expand the attestation list​

Microsoft has explicitly said it will update the CVE/VEX entry if its inventories find other Microsoft products that ship the component; the timescale for that expansion depends on internal inventory efforts and the number of distinct artifacts that need verification. In practice, vendors often begin with a high‑impact product family (Azure Linux) and then extend coverage as automation and artifact provenance checks finish. Until Microsoft publishes additional attestations naming other products, operators should assume uncertainty and verify artifacts they run.

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Final assessment and recommendations​

• Microsoft’s statement that “Azure Linux includes this open‑source library and is therefore potentially affected” is an accurate, product‑scoped attestation and is authoritative for Azure Linux customers. Treat Microsoft’s VEX/CSAF output as the canonical remediation signal for Azure Linux.
• That attestation does not prove that other Microsoft products are unaffected. Operators must independently inventory and verify any other Microsoft‑provided images, kernels, and appliances they run, and they should not assume global coverage from a single product attestation.
• Practical immediate steps: apply Microsoft’s Azure Linux updates if you use those images; inventory and scan other Microsoft artifacts in your estate; tighten BPF policies and monitor kernel telemetry while rollouts complete.

Microsoft’s shift to machine‑readable attestations (CSAF/VEX) is a notable improvement for security automation and fast triage, but the model is incremental. Use vendor attestations to prioritize response — but rely on artifact inspection, SBOMs, and runtime telemetry for complete assurance across a diverse Microsoft artifact footprint.

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Caveat: definitive proof that a given Microsoft SKU (beyond Azure Linux) is affected requires either Microsoft to publish an explicit VEX/CSAF attestation naming that SKU or for you to inspect the artifact (kernel version/commit, SBOM, binary scan). Until one of those facts is available, treat other Microsoft artifacts as potential carriers and verify accordingly.

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Source: MSRC Security Update Guide - Microsoft Security Response Center