CVE-2025-37979 Explainer: Azure Linux Attestation and Qualcomm ASoC Buffer Overflow

A buffer‑overflow bug in the Linux kernel’s Qualcomm ASoC (audio) support — tracked as CVE‑2025‑37979 — has prompted Microsoft to map the upstream component to its Azure Linux distribution and to advise customers that Azure Linux “includes this open‑source library and is therefore potentially affected.” That vendor attestation is authoritative for Azure Linux, but it does not, on its own, prove that no other Microsoft product ever ships the same vulnerable kernel code. In this feature I explain what the vulnerability is, why Microsoft named Azure Linux, which Microsoft artifacts could — and could not — plausibly be affected, how to verify exposure in your environment, and the practical mitigations you should perform today.

Background / Overview​

The flaw is an out‑of‑bounds access in the SC7280 ASoC (ALSA System-on-Chip) machine driver for Qualcomm’s LPASS audio subsystem. The problem traces back to a prior commit that added new audio port identifiers without raising the constant used to size per‑port arrays. In short: new port ID values can cause an index to exceed the arrays allocated for per‑port state, producing a kernel buffer overflow when the driver’s hw_params and stream handling paths process certain DAIs (digital audio interfaces).
Upstream maintainers accepted a targeted fix: the driver’s port‑count constant is redefined to reflect the full range of possible LPASS port IDs used by the q6dsp interfaces, and a small defensive change prevents illegal indexing. The patch was applied to the kernel sound tree, and the fix has been propagated to subsequent stable kernel snapshots.
Why that matters: a kernel buffer overflow can compromise kernel memory integrity, cause crashes, or — in the hands of a skilled attacker with appropriate access — lead to code execution in kernel context. Whether an overflow is practically exploitable depends on many variables: the runtime kernel configuration, whether the vulnerable driver is built and loaded, the device’s hardware topology, available attack surface, and privilege boundaries on the target system.

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What Microsoft said — and what that wording actually means​

Microsoft’s public advisory for the CVE contains a short FAQ that names Azure Linux (the Microsoft‑maintained distribution descended from CBL‑Mariner) and states the distribution “includes this open‑source library and is therefore potentially affected.” Microsoft also called out that, as part of a transparency initiative, it began publishing machine‑readable CSAF/VEX attestations for Azure Linux and will update CVE/VEX mappings if additional Microsoft products are later found to ship the same upstream component.
Interpreting that text correctly is crucial:

• The statement is a product‑level attestation: Microsoft has inspected Azure Linux artifacts (packages, kernels, or images) and confirmed the presence of the upstream component that maps to the CVE. For Azure Linux customers, that confirmation is actionable and authoritative: treat Azure Linux images as in‑scope for remediation.
• The statement is not a universal exclusion of other Microsoft artifacts. Absence of a named product on the MSRC page is absence of attestation, not proof that other Microsoft products do not contain the same vulnerable code.
• Microsoft has committed to update the mapping if they discover other internal artifacts that ship the component. Until they do, customers and admins should assume other Microsoft‑distributed Linux kernels could be carriers until proven otherwise.

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

Short answer: No — Azure Linux is the only Microsoft product that Microsoft has publicly attested (so far) to include the implicated upstream kernel component. But that attestation doesn’t technically exclude other Microsoft Linux artifacts from carrying the same vulnerable sources; whether they do depends on the actual kernel source and the configuration used to build any given kernel image.
To decide whether other Microsoft products might be affected, consider the primary classes of Microsoft‑distributed Linux artifacts:

• Azure Linux (CBL‑Mariner / Azure Linux images)
• Confirmed attestation. If you run Azure Linux images provided by Microsoft, treat those images as in‑scope and apply vendor patches promptly.
• The WSL2 kernel (Windows Subsystem for Linux)
• The WSL2 kernel source tree distributed by Microsoft includes a broad set of upstream drivers as part of the complete Linux source tree, including the Qualcomm SC7280 ASoC machine driver file. Presence of a file in the source repository does not alone imply it is built into the binary shipped with Windows; kernel build configuration determines which drivers are compiled.
• Microsoft ships an x86_64 WSL2 kernel by default for Windows on x86_64. That WSL kernel uses an x86_64 config that typically disables arm/SoC‑specific drivers (Qualcomm SoC machine drivers are ARM platform specific). In practice, the default shipped WSL2 kernel for typical Windows desktops is highly unlikely to include an ARM SoC audio driver compiled in or loaded on a Windows x86 system. However, customers who build or install a custom WSL kernel (or use an arm64 WSL kernel or custom modules) must verify their build configuration.
• Azure Marketplace / platform images, AKS node images, and custom Azure VM kernels
• Azure hosts, Marketplace images, and managed node images can ship a variety of kernels supplied by Microsoft or by independent vendors. If those kernels derive from the same upstream code range that contained the vulnerable commit and the kernel config enabled SND_SOC_QCOM / SND_SOC_SC7280, they could be affected. Whether a particular Azure image is affected is an artifact‑level question.
• Windows proper (NT kernel, Edge, Office, etc.)
• Not affected. The vulnerability is strictly in Linux kernel ASoC audio driver code. Windows components do not contain the Linux kernel driver and are not impacted by this CVE.
• Azure Sphere and other specialized Microsoft OS artifacts
• Azure Sphere uses a different OS architecture; any claim of exposure must be verified on a case‑by‑case basis.

Put plainly: Azure Linux is the only Microsoft product Microsoft has mapped publicly to this specific upstream component so far; that is a critical and useful signal. It is not a guarantee that other Microsoft kernels or images are immune. Artifact‑level verification remains necessary.

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Technical analysis — attack surface and exploitability​

Understanding where the vulnerability matters in practice requires two facts:

• The vulnerable code is hardware‑specific. It targets the LPASS audio subsystem on Qualcomm SC7280 SoC platforms. That means the code is only useful when the kernel is running on hardware that provides the matching device tree nodes or when the system has a SoundWire / MI2S audio path configured to use those DAIs.
• Kernel code presence vs. kernel code execution. The mere existence of source files in source‑control does not create a runtime vulnerability; the driver must be built into the kernel (or built as a loadable module and then loaded) and the audio subsystem must be used by the device.

Realistic exploitation scenarios require one or more of the following:

• A system that runs on SC7280 hardware (or a binary compatible platform) with the vulnerable driver built in; local or local‑adjacent attackers (or a malicious local userland program) might be able to stimulate the driver through ALSA/SoundWire control paths and trigger the overflow.
• An attacker who can cause the kernel to parse maliciously crafted audio configuration data from a device exposed to the system (e.g., a malicious external audio device, driver interface, or compromised user‑space component that exercises the driver).
• Remote exploitation is not impossible in all cases, but is constrained: to reach this driver remotely, an attacker would need a chain that gives them the ability to interact with the audio driver from outside — for example, by convincing a privileged service to perform actions that reach the driver — which ordinarily raises the bar considerably.

In short, this CVE presents a higher risk for devices that actually use the Qualcomm SC7280 platform and for kernels that include and load the affected sound driver. For general Linux servers running on x86_64 cloud instances, the practical risk is low unless an artifact in the chain was built with the vulnerable driver for ARM and then misapplied.

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How to verify whether your systems are at risk (practical checks)​

You must perform artifact‑level checks. The following tests will determine whether a given Linux system carries or loads the vulnerable driver.
For a running Linux VM / server (shell commands):

• Identify the running kernel:
• uname -r
• Check for the driver module on disk:
• grep -i sc7280 -R /lib/modules/$(uname -r) || true
• ls /lib/modules/$(uname -r)/kernel/sound/soc/qcom || true
• Check kernel config for the SND_SOC_SC7280 option:
• zgrep SND_SOC_SC7280 /proc/config.gz || zgrep SND_SOC_SC7280 /boot/config-$(uname -r) || true
• List loaded modules:
• lsmod | grep -i sc7280 || true
• If modules are present, attempt to modinfo:
• modinfo msm-snd-sc7280 || true

For WSL2 instances (from PowerShell / Command Prompt on Windows):

• Query the WSL kernel running in the distribution:
• wsl -d <distro> -- uname -r
• Inside the distribution run the same Linux checks listed above (uname, check /lib/modules, zgrep config).
• If you use the Microsoft‑shipped WSL kernel on x86_64, note that the default kernel is built for x86_64. Presence of the sc7280 source file in the WSL source tree does not automatically imply the prebuilt WSL kernel contains the driver.

For Azure images and marketplace VM images:

• Check each image type used in your environment: run the kernel checks above on any VMs built from Microsoft images.
• For managed node images (AKS, VM scale sets), check the node kernel and modules via ssh or via your cluster management tools.

Important verification notes:

• If a check shows the SND_SOC_SC7280 option is set to “m” (module) or “y” in the kernel config and /lib/modules contains the driver, you should assume the system is potentially vulnerable until you update the kernel.
• If the driver is not present on disk or the kernel config disables it, the system is not exposed to this driver vulnerability (though other unrelated kernel vulnerabilities may still apply).

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Immediate mitigation and remediation guidance​

If you discover the vulnerable driver is present in your systems, take these steps:

• Apply vendor or upstream updates as the primary remediation.
• For Microsoft‑supplied Azure Linux images, apply Microsoft’s published kernel update or image patch as recommended in the MSRC advisory.
• For other distributions, apply the distribution’s kernel updates containing the upstream fix (the fix is present in kernel trees and should be present in updated distro kernel packages or backports for supported releases).
• If you cannot immediately update, consider temporary mitigations:
• Blacklist the driver (if it’s a module) so it cannot be loaded:
• echo "blacklist msm-snd-sc7280" | sudo tee /etc/modprobe.d/blacklist-sc7280.conf
• sudo update-initramfs -u && reboot (or the equivalent for your distribution)
• If the driver is built into the kernel (not a module), blacklisting is ineffective; you must update the kernel.
• Limit attack surface:
• Remove or restrict access to local device nodes that can control the audio subsystem if practical.
• Enforce strict least privilege for services that interact with audio devices.
• Monitor and audit:
• Watch for signs of kernel instability or crashes in dmesg and syslog that could indicate attempts to trigger the bug.
• Keep an inventory of all kernel artifacts you run (WSL kernels, custom kernels, Marketplace images, container host kernels) and automate verification where possible.

Why patching is best: blacklisting will (at best) prevent the driver from loading, but the safest, long‑term fix is to run a kernel with the upstream patch that corrected the indexing and port‑count logic.

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Specific checks and commands (copy‑ready)​

• Confirm whether the driver file exists in the kernel’s modules:
• uname_r=$(uname -r)
• sudo find /lib/modules/"$uname_r" -type f -name "sc7280" -print || echo "no sc7280 files found"
• Check kernel config for the build option:
• sudo sh -c 'if [ -f /proc/config.gz ]; then zgrep SND_SOC_SC7280 /proc/config.gz || true; else grep SND_SOC_SC7280 /boot/config-$(uname -r) || true; fi'
• On WSL, query from Windows:
• wsl -d <distro> -- uname -r
• Then run the file and config checks inside the distro.

If you find SND_SOC_SC7280 set to Y or M and driver files are present under /lib/modules, schedule an urgent kernel update and treat the system as in‑scope.

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What to tell affected customers and security teams​

• If you run Azure Linux images provided by Microsoft: follow Microsoft’s advisory and apply the published kernel update for Azure Linux without delay. Microsoft’s product‑level attestation means Azure Linux is a confirmed hit and should be remediated per the vendor instructions.
• If you run other Microsoft artifacts (WSL, Marketplace images, AKS node images, custom kernels listed by Microsoft): do not assume they are safe. Perform the artifact‑level verification described above. If a given artifact contains the driver, patch it immediately.
• If you manage diverse fleets, automate the checks. Add the kernel/config/module checks to your baseline host‑hardening and asset‑management scripts so you can rapidly identify any images that include the vulnerable driver.
• If you’re a software vendor or device OEM that ships kernels or images that may include Qualcomm SoC drivers, verify your kernels and post an attestation or an advisory for your customers. The upstream fix is a small, well‑scoped change; shipping updates is typically straightforward.

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Strengths and caveats in Microsoft’s approach​

Microsoft’s attestation that Azure Linux includes the implicated upstream component is a welcome step: it gives customers a precise, automatable signal about one product that Microsoft maintains. The public VEX/CSAF roll‑out for Azure Linux improves transparency and helps reduce noisy false positives for security scanners.
However, the approach has limitations that customers must understand:

• Strength: an attestation is a clear and useful indicator for a named product. If you run Azure Linux, that statement is actionable and authoritative.
• Weakness: attesting one product at a time necessarily leaves a window where other Microsoft artifacts remain un‑attested. Customers who consume multiple Microsoft‑published Linux images or kernels must treat these as unverified until attested.
• Operational risk: enterprises that rely on broad, centralized vulnerability scanning will still need artifact‑level checks to know whether the kernel code is present in their particular images or custom builds. Vendor attestation is complementary to, not a substitute for, artifact inspection.

Microsoft has committed to update its VEX/CSAF records as it discovers additional affected products. That commitment is important, but until further mappings are published, the safe operational posture is to verify kernels you actually run.

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Final takeaways and recommended checklist​

• Treat Azure Linux images as in‑scope. Apply Microsoft’s Azure Linux kernel updates now.
• Do not interpret Microsoft’s attestation for Azure Linux as a universal guarantee that other Microsoft artifacts are free of the vulnerable code.
• Immediately inventory the kernels and images you run (WSL, AKS nodes, Marketplace VMs, custom kernels) and run the artifact checks listed above to determine presence of SND_SOC_SC7280 or related driver modules.
• Where the vulnerable driver is present, update the kernel to a patched release. If update is temporarily impossible, blacklist the module (if modular) and reduce local access to the audio subsystem.
• Automate these checks in your CI/CD and fleet scanning tooling so future similar disclosures can be triaged rapidly.

This vulnerability is a concrete reminder that vendor‑level attestations improve security clarity but do not replace artifact‑level verification. Azure Linux’s attestation is authoritative for that product — act on it — and treat other Microsoft‑distributed Linux artifacts as unverified until you or Microsoft confirm their status.

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Source: MSRC Security Update Guide - Microsoft Security Response Center