CVE-2025-37882: Azure Linux Attestation and Cross Artifact Exposure

Microsoft’s brief advisory that “Azure Linux includes this open‑source library and is therefore potentially affected” is accurate — but it is a product‑scoped attestation, not proof that no other Microsoft product contains the same vulnerable Linux kernel component; operators must treat Azure Linux as definitively in‑scope while also performing artifact‑level checks across Microsoft’s other Linux artifacts (WSL kernels, CBL‑Mariner/azure host kernels, Marketplace images) until Microsoft expands its CSAF/VEX attestations.

Background / Overview​

CVE‑2025‑37882 is a Linux kernel defect fixed upstream in May 2025 that corrects a race in xHCI isochronous Ring Underrun/Overrun event handling. The problem arises because the TRB (Transfer Request Block) pointer referenced by xrun events may reflect the queue state at the time the error occurred — or be NULL on older host controllers — but by the time the kernel processes the event a new TD (Transfer Descriptor) might already occupy that ring position. In racey conditions (for example, when interrupt moderation increases IRQ handling latency or under heavy system load) this can cause the kernel to treat a newly queued TD as if it matched the xrun event, which risks premature handing back of a TD, potential data loss, and use‑after‑free conditions in the xHCI host controller implementation. The fix avoids completing TDs on xrun events and alters warning behavior so the kernel does not assume the TRB pointer is always the queued TD. Upstream stable commits and distro advisories document the change. This article answers the customer question posed against Microsoft’s MSRC wording, explains what Microsoft’s attestation practically means, verifies the technical facts with independent sources, and provides a prioritized, actionable playbook to determine exposure and remediate affected systems across Microsoft-supplied artifacts.

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What Microsoft actually said — and what that means​

The wording and its operational meaning​

Microsoft’s public text — that Azure Linux includes this open‑source library and is therefore potentially affected — is an authoritative, machine‑readable attestation tied to the Azure Linux product family. It means Microsoft inspected and validated the inventory for Azure Linux images and concluded they include the upstream code referenced by the CVE; Microsoft is publishing that result as part of its CSAF/VEX rollout and has stated it will update the CVE entry if additional Microsoft products are identified as carriers of the same code. That is a product‑inventory statement: definitive for Azure Linux as of the date of publication, not a universal exclusion for other Microsoft SKUs.

Why that nuance matters​

• Authoritative for Azure Linux: If you run Azure Linux images supplied by Microsoft, that attestation is the definitive signal to act on now.
• Not proof of absence elsewhere: Other Microsoft‑shipped Linux artifacts (for example the Windows Subsystem for Linux (WSL2) kernel, CBL‑Mariner artifacts, linux‑azure images used for certain VM families and Marketplace images) can, in principle, include the same upstream kernel code depending on kernel version and build-time configuration. Microsoft’s phased VEX publication simply means those products may not yet have completed their inventory mapping.
• Operational consequence: Treat Azure Linux as “confirmed potentially affected.” Do not assume everything else from Microsoft is unaffected — validate each artifact you run.

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The technical facts: what CVE‑2025‑37882 fixes and where​

What the bug is, in plain terms​

• Component: Linux kernel USB xHCI driver (drivers/usb/host/xhci-ring.c).
• Fault: Race between event handling and ring enqueueing on isochronous rings. The TRB pointer in xrun events may not reflect the current queued TD when the handler runs, or may be NULL on older controllers.
• Risk: Completing the wrong TD or completing a TD after it has been requeued/changed can lead to data loss or buffer UAF (use‑after‑free) conditions at the host controller level.
• Fix: Do not complete TDs on xrun events and remove misleading warnings when the queued TD does not match the TRB pointer; add safe handling of xrun events when the skip flag is clear so a TD stuck in an “error mid‑TD” state can be completed safely.

Upstream fixes and tracked commits​

The Linux kernel CVE announcement and upstream stable backports list the precise fixes. The patch was merged into the stable trees and the kernel team recommended updating to the latest stable kernel; the linux-cve-announce & stable commit notes identify fixes in versions such as 6.12.26, 6.14.5, and the 6.15-rc1 branch (commit hashes are available in the upstream stable commit list). Operators should map their kernel package changelogs to these commits or update to kernel versions that include them.

How distros classified it​

Mainstream distributions (Ubuntu, Debian, SUSE, Red Hat, Oracle Linux) published advisories describing the issue and labeled it as a kernel robustness/availability issue with a medium-to-moderate operational priority; vendor CVSS scoring varies by vendor and operational assumptions. That classification reflects the local/host‑level vector and the absence of established remote exploitation in the wild at disclosure time.

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Is Azure Linux the only Microsoft product that includes the vulnerable code?​

Short, operational answer​

No — Azure Linux is not necessarily the only Microsoft product that could include the affected kernel code, but it is the only Microsoft product Microsoft has publicly attested as including the component at the time of Microsoft’s advisory. The attestation is a product‑scoped inventory result for Azure Linux and Microsoft has committed to expand its CSAF/VEX outputs as further inventories complete.

Why other Microsoft artifacts could also be carriers​

Microsoft maintains several distinct Linux kernel or kernel-adjacent artifacts that are plausible carriers:

• WSL2 kernel binary / WSL2‑Linux‑Kernel repository: Microsoft publishes the kernel source and configurations for WSL2 on GitHub; those kernels are built and shipped as part of Windows updates or WSL releases and can include many of the same driver subsystems depending on config and version. If a WSL kernel branch or release used a vulnerable upstream revision or included the xHCI ring code (and if the module is built-in or available), that WSL instance could be affected.
• CBL‑Mariner / linux‑azure images and Marketplace images: Microsoft’s internal distro lineage and cloud host images are regularly rebuilt and may include kernels built from upstream trees. Whether they include the vulnerable code is an artifact-by-artifact question determined by kernel version and CONFIG_* flags.
• Other Microsoft container/virtual appliance images: Marketplace VM images, managed service node images, or vendor bundles that include a Linux kernel can carry the same code if their build provenance maps to vulnerable commits.

Therefore, the absence of a Microsoft‑wide attestation is not evidence that other Microsoft products are safe — it only indicates Microsoft has completed and published the inventory for Azure Linux first.

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How to determine if a Microsoft artifact you run is affected (practical checks)​

These steps should be automated where possible and performed immediately for Azure Linux VMs and for any other Microsoft‑supplied Linux artifact in your estate.

1. Identify the running kernel and package provenance​

Run on the Linux instance:

1. uname -a
2. cat /proc/version or rpm -q --queryformat '%{NAME}-%{VERSION}-%{RELEASE}\n' kernel-$(uname -r)
3. zcat /proc/config.gz | grep -i xhci

These commands show the running kernel version and whether kernel config includes xHCI support or if the driver is modular. If the kernel version is on or after a fixed upstream version that includes the stable commit(s) referenced for CVE‑2025‑37882, the instance is likely fixed. If distro package changelogs list the upstream commit IDs, that is authoritative.

2. Check whether the xHCI ring driver is present and how it’s built​

• If xHCI is a module:
  • lsmod | grep xhci
  • find /lib/modules/$(uname -r) -type f -name 'xhci*' -print
• If built-in:
  • Search the kernel image symbol table:
  • grep -i xhci /boot/config-$(uname -r) or read the .config used to build the kernel.

If the driver binary path contains drivers/usb/host/xhci-ring.c or the module name is present, the artifact contains the code path referenced in the CVE.

3. Validate the kernel package or image contains the upstream fix​

• Consult your vendor/distro security tracker for CVE‑2025‑37882 and map your kernel package to the vendor advisory (Ubuntu, Debian, SUSE, Red Hat, Oracle have entries).
• For Microsoft artifacts: consult Microsoft’s CSAF/VEX outputs for Azure Linux (authoritative) and the MSRC Update Guide; for other Microsoft artifacts (WSL, CBL‑Mariner, Marketplace images) check published changelogs or await Microsoft’s VEX expansion.

4. If you cannot quickly confirm a fix, apply defensive mitigation​

• Restrict access to hot‑plug USB paths or untrusted USB device attach capabilities on sensitive hosts.
• For virtualized environments, limit USB passthrough from untrusted tenants and disable exposing physical USB controllers to untrusted guests.
• Schedule kernel updates for the affected hosts as a first priority. The definitive remediation is the kernel update package that contains the upstream stable commit(s).

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Recommended remediation and verification steps (prioritized)​

1. Patch Azure Linux images immediately per Microsoft’s guidance (Azure Linux attestations mark those images as potentially affected — treat that as the highest operational priority).
2. Map your other Microsoft Linux artifacts (WSL2 instances, Marketplace images, CBL‑Mariner hosts) and run the artifact-level checks above; where you identify a vulnerable kernel, schedule the kernel update.
3. Validate vendor/distro package changelogs: confirm the kernel package lists the upstream commit ID(s) referenced in linux-cve-announce or the vendor advisory. If the package changelog cites the commit, treat the package as patched.
4. Test in staging: apply the kernel update to representative, non‑production hosts first and validate USB device behavior (attach/detach cycles, isochronous transfers for audio/video devices).
5. Reboot or apply livepatches only if the vendor provides them for this fix; kernel updates typically require a reboot unless a vendor-supplied livepatch is available.

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Detection and monitoring guidance​

Because the primary impact is availability and data integrity at the USB/xHCI level (not confirmed RCE), monitoring should focus on kernel logs and USB/iomemory anomalies.

• Kernel logs: watch for xHCI warnings in dmesg / journalctl -k referencing xrun, TRB pointers, TD completion or xHCI ring traces.
• Device symptoms: repeated isochronous stream failures (audio/video stuttering or data loss), unexpected disconnects during high-load USB transfer windows.
• Virtualized hosts: monitor guest-side stall behavior when USB passthrough is used or when interrupt moderation settings have been altered.

Create SIEM rules to match kernel log patterns that vendors and trackers document for this CVE; capture full kernel logs for post‑incident analysis.

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Strengths in the disclosure and vendor response — and the gaps you should watch​

Notable strengths​

• Small, surgical fix upstream: The kernel patch is localized to drivers/usb/host/xhci-ring.c and was backported to stable releases; updating kernels or packages is a straightforward remediation path.
• Distro coverage: Major distributions published advisories, enabling automation in vulnerability scanners and patch management systems.
• Microsoft transparency for Azure Linux: Publishing CSAF/VEX attestations for Azure Linux gives Azure customers an authoritative, machine‑readable signal to act on immediately.

Potential hazards and gaps​

• Attestation scope vs reality: Microsoft’s attestation covers Azure Linux explicitly, but a simple attestation gap does not prove other Microsoft artifacts are unaffected. Customers who only rely on the presence or absence of an MSRC attestation risk false reassurance.
• Artifact proliferation: Microsoft ships multiple kernel artifacts (WSL2 kernels, CBL‑Mariner builds, linux‑azure kernels and Marketplace images). Each is a separate build and could carry the vulnerable code depending on kernel version and build flags; a single attestation does not cover them all.
• Vendor scoring variance: Differing CVSS and severity assignments across distros can produce inconsistent prioritization signals for mixed environments; prioritize by exposure and function (hypervisors, multi‑tenant hosts, or hosts accepting USB devices from untrusted parties).

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Practical checklist for Windows and hybrid operations teams​

• For Azure customers:
  • Identify all VMs running Azure Linux images and apply the Microsoft‑published kernel updates or new images as directed. Treat these as high priority because Microsoft has attested Azure Linux as potentially affected.
• For WSL users and developer machines:
  • From inside WSL2: uname -r and compare the kernel release to the versions that include the fix; if using the Microsoft WSL2 kernel, consult the WSL2-Linux-Kernel GitHub repository and release notes to confirm whether the branch/tag in use includes the upstream backport. Consider updating WSL kernel via the Windows Update channels or custom kernel if needed.
• For CBL‑Mariner / Azure host images:
  • Confirm whether your CBL‑Mariner artifacts or host kernels include the fix via vendor advisories or the kernel package changelog. If not, schedule the patch with urgency for hosts that accept USB attachments or run untrusted workloads.
• For virtualization infrastructure:
  • Block or tightly control USB passthrough for tenants you do not fully trust. Validate hypervisor kernel updates for any host kernels that include xHCI support.
• For monitoring and detection:
  • Deploy kernel log parsing rules for xhci/xrun-related messages and escalate any stream errors or repeated isochronous failures for forensic capture.

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Verification: mapping to upstream commits and vendor fixes​

• The linux-cve-announce message and stable commits list the specific commit hashes and the kernel releases where the fix landed (for example, fixes applied to stable branches represented by commits referenced in the linux-cve-announce post). Administrators should map those commit IDs to their vendor’s package changelog to definitively confirm patch status.
• Use vendor advisories (Ubuntu, Red Hat, SUSE, Oracle) to cross‑check whether the distribution kernel packages you run include the upstream change; these advisories are the authoritative evidence downstream.

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Final assessment and recommended posture​

Microsoft’s public attestation that Azure Linux includes the relevant open‑source library and is therefore potentially affected delivers a necessary, machine‑readable remediation signal for Azure Linux customers — act on that immediately. However, the attestation is product-scoped; Azure Linux being attested does not mathematically exclude other Microsoft artifacts from carrying the same vulnerable upstream kernel code. To be defensible:

• Treat Azure Linux as confirmed in‑scope and remediate per Microsoft guidance without delay.
• Simultaneously inventory and verify other Microsoft-supplied Linux artifacts (WSL2 kernels, CBL‑Mariner images, linux‑azure/Marketplace images) using the kernel and module checks listed above and patch where the vulnerable driver is present.
• Rely on multiple independent sources to validate fixes: upstream linux-cve-announce listing the stable commits, NVD/distro advisories, and vendor package changelogs are the defensible chain of evidence for remediation.

This combined approach — immediate remediation for Azure Linux, artifact‑level validation across other Microsoft kernels, and reliance on upstream and vendor mappings to confirm fixes — is the practical and defensible way to manage CVE‑2025‑37882 across Windows‑centric and hybrid estates.

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Conclusion
Microsoft’s statement about Azure Linux is helpful and correct for that product family: Azure Linux has been inventory‑checked and Microsoft has published a CSAF/VEX attestation indicating it includes the open‑source component implicated by CVE‑2025‑37882. That attestation is authoritative for Azure Linux, but it is not an all‑products proof of absence. Organizations must act immediately on Azure Linux updates, and at the same time perform per‑artifact verification and patching for other Microsoft‑supplied Linux kernels (WSL2, CBL‑Mariner, linux‑azure, Marketplace images) until Microsoft’s inventory expansion explicitly attests those artifacts as not affected or as remediated. Use the kernel version, module presence, and vendor changelog checks listed above to validate your environment; when in doubt, apply the upstream/ vendor kernel updates that include the stable commits referenced in the linux-cve-announce and distribution advisories.

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Source: MSRC Security Update Guide - Microsoft Security Response Center