Microsoft’s concise advisory — that
Azure Linux includes this open‑source library and is therefore potentially affected — is accurate for the Azure Linux product family, but it is
not a categorical guarantee that no other Microsoft product could include the same vulnerable component. The phrase is a product‑scoped attestation: Microsoft has inventory‑checked Azure Linux and published a machine‑readable status for that product, and it has committed to update the CVE/VEX/CSAF mapping if additional Microsoft products are later discovered to ship the same upstream library.
Background / Overview
The vulnerability tracked as
CVE‑2025‑38074 affects the Linux kernel vhost‑scsi code and was fixed by ensuring proper synchronization — specifically, to “protect vq->log_used with vq->mutex.” Public vulnerability databases (NVD, Debian/Ubuntu trackers and distro advisories) describe the bug as a host‑side synchronization issue where the vhost‑scsi completion path can access vq->log_base after vq->log_used has been cleared, potentially causing invalid memory writes that can corrupt QEMU userspace memory. Microsoft’s MSRC advisory for the CVE states that
Azure Linux includes this open‑source library and is therefore potentially affected, and that Microsoft began publishing machine‑readable CSAF/VEX attestations (starting with Azure Linux) and will update CVE entries if additional Microsoft products are found to include the component. That language is an inventory statement, not a product‑exclusion statement.
This article unpacks what Microsoft’s wording means in practice, explains how defenders should interpret it, shows how to verify exposure across Microsoft artifacts and images, and provides operational triage and remediation guidance.
What Microsoft actually said — why wording matters
Microsoft’s advisory performs two distinct functions:
- A definitive product attestation: Azure Linux (the Microsoft‑published Linux distro lineage) has been inspected and the implicated component was found; therefore Azure Linux images are explicitly in scope for remediation and automation.
- A procedural commitment: Microsoft will expand its CSAF/VEX attestations to other products over time and will update the CVE/VEX metadata if additional Microsoft products are identified as carriers of the same open‑source code.
Why that distinction matters: a CSAF/VEX attestation answers “Which named product builds ship this upstream component?” It does not imply that every other product that is not yet attested is automatically clean. Large vendors publish attestations in phases because exhaustive inventory across all product lines, images, kernels and appliances takes time. Treat the attestation as authoritative for the product it names and
unknown for everything else until verified.
Short answer to the user’s question
- Is Azure Linux the only Microsoft product that includes this open‑source library and is therefore potentially affected by CVE‑2025‑38074?
- Strict reading of the MSRC attestation: Yes — Azure Linux is the only Microsoft product Microsoft has publicly attested (so far) as including this component.
- Practical security reading: No — Azure Linux is not necessarily the only Microsoft artifact that could carry the vulnerable code. Other Microsoft‑distributed images, kernels, or appliances may include the same upstream code depending on kernel version, configuration flags, and packaging choices; absence of a VEX/CSAF attestation for a product is absence of evidence, not evidence of absence.
Why other Microsoft artifacts could still be carriers
The Linux kernel and related virtualization components are
build‑time artifacts. The presence or absence of a particular code path depends on:
- Kernel version and stable commit range (which commits are included).
- Kernel configuration flags (CONFIG_* options that toggle drivers and subsystems).
- Whether code is compiled into the kernel or built as a module.
- Packaging and backport decisions made by the vendor when assembling a distribution or image.
Microsoft ships multiple distinct Linux artifacts that are plausible carriers depending on those variables:
- Azure Linux / CBL‑Mariner lineage (explicitly attested).
- linux‑azure / Azure‑tuned kernels used for some VM SKUs and images.
- WSL2 kernel builds (Windows Subsystem for Linux). These are Microsoft‑built kernels with public sources; whether they include a given code path depends on the kernel config used for the WSL kernel. Public WSL kernel configs sampled historically often have many sanitizers disabled, but operators must verify current configs.
- Azure Marketplace VM images and third‑party appliances — these might use Microsoft kernels or vendor kernels; each image is a unique artifact to inspect.
- Container host images and curated node images (AKS / node pools) — depending on how they were built, they may include vulnerable kernel bits or userspace helpers.
Because every artifact is a separate build, each must be individually verified until Microsoft expands the VEX/CSAF mapping or issues additional product attestations.
How to verify whether a Microsoft artifact you run is affected
Below is a prioritized set of checks for administrators and security teams. Perform these on images, hosts, and VM templates you run in your estate.
1. Inventory and map artifacts
- Use your asset inventory and configuration management database to list:
- Azure Linux images and versions.
- Azure Marketplace images and partner appliances in use.
- Hosts that run WSL2 (Windows clients/servers with WSL enabled).
- Any linux‑azure / Microsoft‑provided kernel packages in your environment.
- Identify specific kernel binaries and QEMU/vhost packages backing each artifact.
2. Verify kernel and module presence (host and guest)
- On a running Linux instance (host or guest), get the kernel version:
- uname -r
- Check if the vhost/vhost_scsi functionality is present or loaded:
- lsmod | grep -E "vhost|vhost_scsi"
- Confirm whether vhost‑scsi is built into the kernel or available as a module:
- zgrep CONFIG_VHOST /proc/config.gz || grep -E "CONFIG_VHOST|CONFIG_VHOST_SCSI" /boot/config-$(uname -r)
- Check QEMU version (on the host) since the issue interacts with QEMU userspace:
- qemu-system-x86_64 --version (or your QEMU package metadata)
3. Search artifact SBOMs / package changelogs
- If you consume SBOMs or Microsoft’s CSAF/VEX outputs, map the CVE ID and component name to your images. Use Microsoft’s VEX/CSAF outputs where available to automate the mapping for attested products.
4. Inspect logs and telemetry for indicators
- Kernel logs containing vhost or vhost‑scsi stack traces or QEMU errors are high‑value telemetry.
- Use: journalctl -k | grep -iE "vhost|vhost_scsi|vq->log_base|vhost_add_used"
- Look in QEMU process logs for corrupted memory writes or unexpected gfree calls linked to vq->log_base access.
5. If in doubt, treat any Microsoft artifact that contains the vhost/vhost_scsi component as potentially exposed until proven otherwise.
(These verification steps are tactical and reproducible; Microsoft’s VEX/CSAF attestation is authoritative for Azure Linux but cannot replace artifact‑level checks in other product families.
Practical triage and remediation checklist
Priority ordering depends on exposure model. CVE‑2025‑38074’s attack vector is local/host‑to‑QEMU interaction (guest or host side), so prioritize multi‑tenant and public cloud hosts first.
- Highest priority
- Hypervisor hosts and nodes that present vhost devices to untrusted guests.
- Multi‑tenant or shared infrastructure where one compromised tenant can cause host instability.
- High priority
- Hosts running QEMU with vhost acceleration enabled.
- VM images used as build agents or CI runners that could execute untrusted guest payloads.
- Medium priority
- Single‑tenant desktop hosts or tightly controlled servers.
Remediation steps (recommended):
- Patch the kernel and components
- Apply vendor/distro kernel updates that include the upstream stable commits addressing CVE‑2025‑38074. Upstream stable commits and distribution backports are tracked across NVD, Debian, Ubuntu trackers.
- Update QEMU packages to vendor‑published fixed versions where applicable.
- Reboot hosts into the patched kernel
- Kernel fixes require a reboot to take effect; coordinate maintenance windows.
- Apply host‑side mitigations if immediate patching is impossible
- Temporarily disable vhost acceleration where feasible (this may impact performance).
- Restrict which guests can use vhost devices.
- Harden management plane access and restrict hotplug device operations.
- Validate fixes
- Confirm package changelog or kernel patch notes contain the commit IDs associated with the CVE.
- Verify no new vhost‑scsi completeness stack traces or QEMU userspace gfree errors appear in logs.
- Reassess inventory and automation
- Consume Microsoft’s CSAF/VEX outputs where available and embed them into vulnerability triage automation for Azure Linux and later attested product families.
Detection and hunting playbook
- Hunting signals
- Kernel oopses with call sites containing vhost, vhost_scsi, vhost_add_used, vhost_add_used_n.
- QEMU logs showing invalid memory writes or aborts referencing vq->log_base.
- Example commands
- Identify loaded modules: lsmod | egrep "vhost|vhost_scsi"
- Check kernel logs: journalctl -k --no‑hostnames | egrep "vhost|vhost_scsi|vhost_add_used|vhost_add_used_n"
- Dump QEMU process stderr logs and correlate timestamps with kernel oopses.
- Response play
- Isolate affected hosts from multi‑tenant clusters if unexplained repeated oops occur.
- Capture QEMU process memory/core if applicable for forensic analysis (be mindful of privacy and legal constraints).
- Apply patches and then validate by rerunning previously failing workloads in a staging group before full rollout.
How Microsoft’s CSAF/VEX attestation model helps — and where it doesn’t
Microsoft’s move to publish machine‑readable CSAF/VEX attestations is a positive transparency step. For the product families Microsoft has mapped, the VEX entries provide a deterministic “Known Affected / Not Affected / Fixed / Under Investigation” signal that automation can consume. Azure Linux was an early target for that program; the MSRC entry for CVE‑2025‑38074 is an example of a product‑level attestation.
Key operational takeaways:
- For Azure Linux operators: treat Microsoft’s attestation as authoritative and follow Microsoft’s remediation guidance.
- For operators of other Microsoft artifacts: do not assume “no mention = not vulnerable.” Perform artifact‑level checks (SBOM, kernel config, module presence, package changelogs) until Microsoft publishes additional attestations covering those products.
Practical commands and examples (cheat sheet)
- Find running kernel: uname -r
- Check if vhost modules are loaded: lsmod | grep -E "vhost|vhost_scsi"
- Inspect kernel config for vhost: zcat /proc/config.gz | grep -i VHOST || grep -i VHOST /boot/config-$(uname -r)
- Find QEMU package version: dpkg -l | grep qemu || rpm -qa | grep qemu
- Look for kernel log indicators: journalctl -k --since "24 hours ago" | egrep -i "vhost|vhost_scsi|vhost_add_used"
- Use package changelog to confirm patch: apt changelog linux-image-$(uname -r) | sed -n '1,120p' (Debian/Ubuntu style)
Risks and caveats — what cannot be verified externally
- Only Microsoft can definitively assert which all Microsoft product SKUs and internal images include the vulnerable upstream component. Microsoft’s public attestation lists Azure Linux as a confirmed carrier; whether other Microsoft products include the library depends on their individual build pipelines and must be declared by Microsoft or checked by artifact inspection. This limitation is a procedural reality — vendors publish attestations in phases, and absence of an attestation is not proof of absence. Treat any such claim beyond Microsoft’s published attestations as unverifiable until Microsoft confirms or until you inspect artifacts yourself.
- Public trackers (NVD, Debian, Ubuntu) confirm the technical facts and the upstream fix, but do not speak to proprietary or internal Microsoft images beyond publicly‑published artifacts. Use their technical details to identify affected kernel versions and backport commit IDs to match against your deployed binaries.
Recommended next steps for operators
- Consume Microsoft’s CSAF/VEX output for Azure Linux (automation) and mark those artifacts as high priority for patching.
- Inventory all Microsoft‑provided Linux artifacts you run (WSL, linux‑azure kernels, Marketplace images, custom golden images). Treat them as separate verification targets.
- Run the verification checklist in this article on representative hosts and images. Patch and reboot hosts where the kernel or QEMU packages match the vulnerable commit ranges.
- Harden management‑plane access and control hotplug/device attach operations for the short term if you cannot immediately patch.
- Integrate Microsoft’s future VEX/CSAF attestations into vulnerability triage pipelines so that new attestations automatically update your scope and priorities.
Conclusion
Microsoft’s statement that
Azure Linux includes the open‑source library and is therefore potentially affected is an accurate, authoritative attestation for Azure Linux images; it is also deliberately scoped and procedural. It is not the same as an explicit denial that no other Microsoft product could include the same vulnerable code. Operational security teams should treat Azure Linux as a confirmed hit and remediate accordingly, while also performing artifact‑level verification across other Microsoft images, kernels, and Marketplace appliances until Microsoft completes broader VEX/CSAF attestations or the artifacts are otherwise proven clean. In short: Azure Linux is the only Microsoft product publicly attested so far, but it is not necessarily the only possible carrier — verify, patch, and monitor.
Source: MSRC
Security Update Guide - Microsoft Security Response Center