Azure Linux Attestation for CVE-2024-46748 and CacheFiles

The short, practical answer is: No — Azure Linux is not necessarily the only Microsoft product that could include the vulnerable cachefiles code, but it is the only Microsoft product Microsoft has publicly attested (so far) to ship the implicated upstream component for CVE‑2024‑46748. That MSRC wording is an authoritative, product‑scoped inventory statement for Azure Linux; it is not a categorical guarantee that other Microsoft kernels, images, or artifacts do not contain the same vulnerable code.

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Background / Overview​

CVE‑2024‑46748 is a Linux kernel vulnerability that affects the cachefiles subsystem. The upstream fix enforces an upper bound on the size of a subrequest used when writing into the cache: the maximum subrequest size for cache writes is now set to MAX_RW_COUNT to avoid overrunning the maximum write that the backing filesystem can accept. The vulnerability is described in public trackers and vendor advisories as a local, availability-impacting issue: an oversized write could cause corruption or unexpected behavior in cachefiles, with the practical impact typically classified as Denial‑of‑Service or data-integrity risk when exploited in-situ.
Microsoft’s Security Response Center (MSRC) published an advisory that states, in plain terms: “Azure Linux includes this open‑source library and is therefore potentially affected by this vulnerability.” MSRC also documented that Microsoft began publishing machine‑readable CSAF/VEX attestations starting in October 2025 and that MSRC will update CVE mappings if additional Microsoft products are identified as carriers. That phrasing is operationally important: it confirms Azure Linux as a known carrier while leaving open the possibility that other Microsoft artifacts may also ship the same upstream code until those artifacts are specifically inventory‑checked and attested.

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Why Microsoft’s wording matters (attestation vs exclusivity)​

Microsoft’s two short sentences perform different jobs:

• They are an attestation: Microsoft inspected Azure Linux build artifacts and found the upstream cachefiles code implicated by CVE‑2024‑46748. That makes Azure Linux a confirmed in‑scope product for remediation.
• They are not an exclusivity guarantee: the statement does not technically prove that other Microsoft products or kernel images do not include the same upstream code. Microsoft explicitly commits to expanding its machine‑readable VEX/CSAF outputs as it completes inventories for other product families; until that wider inventory is published, absence of a public attestation for a Microsoft product means simply “not (yet) attested,” not “not affected.”

This distinction is subtle but operationally crucial for administrators who run a mix of Microsoft-supplied artifacts: a product‑scoped attestation is a high‑fidelity signal that the named product needs patching, but it does not replace artifact‑level verification across an organization’s estate.

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Technical primer: what cachefiles is and why this fix matters​

What is cachefiles?​

• CacheFiles is a kernel subsystem that allows a local filesystem (often a block device like ext4 or xfs) to act as a cache for remote, slower network filesystems. It typically works with FS‑Cache and a userspace daemon (cachefilesd) to store and manage cached objects. The kernel component is compiled as the cachefiles module or built-in under CONFIG_CACHEFILES.
• CacheFiles is used in a range of scenarios, from improving performance of network-mounted filesystems to serving as a cache for container image distribution in on‑demand read mode. Because it writes data to a backing filesystem, bugs that allow an oversized write can expose the system to corruption, crashes, or other availability impacts.

The bug and the fix​

• The reported problem for CVE‑2024‑46748 is that the code which builds subrequests for cache writes did not properly constrain the size of those subrequests. In some build paths, a subrequest could exceed what the underlying filesystem allowed, creating the risk of overruns. The upstream patch forces the maximum subrequest size to MAX_RW_COUNT, a kernel constant governing the maximum bytes that may be written in a single request to the backing filesystem. That change prevents oversized writes and avoids potential corruption or kernel crashes tied to the cache write path.
• Vendor trackers (NVD, distro advisories, SUSE, Debian/Ubuntu downstreams) classify the fix as moderate in severity where the primary impact is availability (local attack vector), with practical risk depending on whether the cachefiles subsystem is enabled and used on the deployed kernel.

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Which Microsoft products could include the cachefiles code?​

The short operational rule: any Microsoft product or artifact that ships a Linux kernel build containing the cachefiles subsystem (CONFIG_CACHEFILES enabled or the cachefiles module present) could include the vulnerable code prior to being patched. Whether a given Microsoft product includes it is an artifact‑by‑artifact question that depends on:

• Which upstream kernel version and commits were used to build that kernel.
• The kernel configuration flags selected at build time (for example, CONFIG_CACHEFILES, CONFIG_FSCACHE, CONFIG_BLOCK).
• Whether the cachefiles code was compiled in as a module or built-in.
• Packaging choices (kernel image, container base image, appliance image) and whether the image includes the userspace cachefilesd daemon.

Common Microsoft Linux and Linux‑adjacent artifacts that could plausibly ship the cachefiles code include, but are not limited to:

• The Azure Linux distribution (the product Microsoft has attested).
• linux‑azure kernel builds used by some Azure VM SKUs.
• WSL2 kernel images bundled with Windows (the shipped WSL kernel is a Linux kernel build and could include or exclude cachefiles depending on build flags).
• AKS node images, Azure Marketplace VM images, and partner appliances if those images contain a kernel built with CONFIG_CACHEFILES enabled.

Because Microsoft’s initial VEX/CSAF rollout started with Azure Linux, those other artifacts may not be publicly attested yet — but they remain plausible carriers until Microsoft completes product-specific inventories or customers verify artifacts themselves.

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Evidence and independent verification​

To ensure readers can act with confidence, here are independent, verifiable touchpoints you can use to validate both the vulnerability details and Microsoft’s attestation approach:

• The CVE description and summarized fix (set max subreq size to MAX_RW_COUNT) are recorded in the NVD and OSV trackers. These entries document the fix and the affected kernel code path.
• Vendor/distro advisories (for example SUSE and downstream Debian/Ubuntu trackers) classify the practical impact and list patched package or kernel versions. Those advisories can be used to correlate which distribution kernel trees received the upstream commit.
• The Linux kernel’s own documentation and configuration metadata confirm the presence of the cachefiles module and the relevant Kconfig entries (CONFIG_CACHEFILES and related options), allowing operators to check their kernels for the subsystem.
• Microsoft’s public blog and MSRC VEX/CSAF rollout announcement (October 2025) explain the phased approach to machine‑readable attestations — starting with Azure Linux and promising updates for other product families as inventories are completed. That is the source of Microsoft’s phrasing about Azure Linux being “potentially affected.”

In short: the technical fix is upstream and widely tracked; the Microsoft statement is an inventory attestation for Azure Linux and matches their phased VEX strategy.

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Practical guidance: how to determine if you (or your Microsoft artifacts) are affected​

Below are immediate, practical steps you should take if you are responsible for Microsoft-supplied Linux artifacts, images, or kernels.

• Inventory and prioritize
• Identify which Microsoft artifacts you run: Azure Linux images, linux‑azure kernels, WSL2 kernels, AKS node images, Marketplace images, and any Microsoft-supplied containers or appliances.
• Prioritize artifacts that are both Microsoft-supplied and have kernel components (VM images, WSL, container base images with kernel modules) because cachefiles is a kernel-level subsystem.
• Check kernel configuration for cachefiles
• On a running Linux instance, inspect /boot/config-$(uname -r) or use zcat /proc/config.gz to look for CONFIG_CACHEFILES (set to y or m).
• Alternatively, check for the cachefiles module: lsmod | grep cachefiles or modinfo cachefiles to see if the module exists in your kernel image. Kernel doc references describe the Kconfig entries and expected behavior.
• Patch or replace affected kernels
• For Azure Linux: apply Microsoft’s provided updates for the distribution as an immediate priority (MSRC attests Azure Linux as a carrier).
• For other Microsoft artifacts: if your inventory indicates cachefiles is present and the kernel version or vendor advisory maps to the upstream commit range for CVE‑2024‑46748, schedule a patch or kernel replacement. Use vendor/distro advisories (NVD/OSV, distro CVE notices) to pick the correct patched kernel series.
• Mitigations where immediate patching is impractical
• If you cannot immediately patch, consider temporarily disabling the cache or removing the cachefiles module until you can apply a fixed kernel, provided that doing so does not break critical functionality. Disabling the use of FS‑Cache/cachefilesd or removing the cachefiles device will eliminate the attack surface for this CVE. Consult the kernel docs before removing modules in production.
• Use SBOMs and image scanning
• Where possible, rely on Microsoft’s CSAF/VEX files combined with your own software bill of materials (SBOM) and image-scanning tooling to identify artifacts that include the vulnerable code. Microsoft’s VEX rollout will make the attestation information machine‑readable and easier to automate; until that per-product coverage is complete, artifact‑level scanning remains essential.

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Deep dive: likely carriers inside Microsoft’s product ecosystem​

Understanding which artifacts are likely carriers helps prioritize verification.

• Azure Linux (confirmed): MSRC explicitly named Azure Linux. That should be treated as the highest-priority target for patching.
• linux‑azure / VM kernels: Azure frequently ships kernel variants for particular VM families. Those kernel builds may differ in CONFIG flags from Azure Linux distribution builds; they must be checked separately.
• WSL2 kernel images: the WSL2 kernel is a shipped Linux kernel binary inside Windows updates. The kernel configuration used to build WSL2 determines whether cachefiles is included. Microsoft has not universally attested WSL kernels in the same way as Azure Linux yet, so verify your WSL2 kernel config and update through Windows Update where Microsoft provides a fixed WSL kernel.
• AKS node images and Marketplace images: container-hosting node images and marketplace VM images often include a kernel; the build recipe determines whether cachefiles is present. These images may lag the Azure Linux SKU in patch cadence and require independent verification.
• Embedded appliances and partner images: any Microsoft-partner distribution or appliance that uses a Microsoft-supplied kernel build could be a carrier, depending on the build pipeline. Treat these as unknown until attested.

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Risk analysis: who should worry and why​

• High concern: organizations running Azure Linux images in production or any environment where cachefiles is enabled and used. MSRC’s attestation makes remediation urgent for those customers.
• Moderate concern: environments where the kernel includes cachefiles but the subsystem is unused. Presence of code still creates an attack surface; however, real exploitation typically requires local access or the ability to interact with the cache daemon or device. Vendor advisories classify CVE‑2024‑46748 as local with primarily availability impact.
• Lower concern: Windows-only workloads without any Linux kernel images supplied by Microsoft (no WSL, no Azure Linux, no AKS node images). Those artifacts are unlikely to ship cachefiles, but teams should still confirm via inventory.

Operationally, the biggest practical risk is blind spots in inventory: Microsoft’s product-level attestation for Azure Linux is useful, but many organizations run heterogeneous Microsoft artifacts, and any un‑attested kernel image should be treated as "unknown" until verified.

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Strengths and limitations of Microsoft’s approach​

Strengths​

• Transparency and machine readability: Microsoft’s adoption of CSAF and VEX (starting October 2025) is a strong positive step. Machine-readable attestations make it easier for enterprise tooling to automate risk decisions and reduce noisy CVE hits against artifacts that are truly not affected.
• Product-focused clarity: Calling out Azure Linux explicitly gives Azure customers a clear action item: prioritize Azure Linux patches. That reduces uncertainty for that product family.

Limitations / Risks​

• Phased coverage leaves windows of ambiguity: rolling out VEX/CSAF one product family at a time means many Microsoft artifacts remain un‑attested for the short-to-medium term. Absent an attestation, operators must revert to artifact-level verification — a heavier operational burden.
• Artifact heterogeneity: Microsoft ships many kernel builds across services, and a single-line advisory cannot capture that complexity. Administrators cannot assume "not mentioned = not affected."

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Recommended checklist for WindowsForum readers and IT teams​

• For Azure Linux users:
• Apply Microsoft’s security updates for Azure Linux immediately. Treat the MSRC entry as definitive for that product.
• For operators of other Microsoft artifacts:
• Enumerate all Microsoft-provided kernels and images in your environment.
• Check each kernel for CONFIG_CACHEFILES or the presence of the cachefiles module.
• If present, schedule patching to a kernel that includes the upstream fix for CVE‑2024‑46748.
• If patching isn’t immediately possible, consider disabling the cache or unloading the cachefiles module until patched.
• For defenders and scanners:
• Integrate the MSRC VEX/CSAF feed into your vulnerability management tooling to automatically reconcile Microsoft’s attestations with local SBOMs and inventory. Where coverage is incomplete, fall back to module/kernel config checks.

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Final assessment and conclusion​

Microsoft’s MSRC advisory for CVE‑2024‑46748 is correct and useful: it tells Azure Linux customers they must treat the distribution as potentially affected and prioritize remediation. At the same time, the advisory’s phrasing and Microsoft’s documented VEX rollout plan make it clear this is a product‑scoped attestation rather than a universal "only Azure Linux" declaration. In practical terms, that means:

• If you run Azure Linux: patch now. Microsoft has attested Azure Linux and will publish VEX/CSAF details to make automation straightforward.
• If you run other Microsoft-supplied kernels or images (WSL2, linux‑azure, AKS node images, Marketplace images): do not assume safety. Verify kernel configs and module presence, and patch if the subsystem is present or in use. Use SBOMs and image scanning to accelerate discovery.
• For security posture: Microsoft’s move to machine‑readable VEX/CSAF is a positive direction, but until VEX coverage broadens, customers and operators must retain artifact-level verification as part of their vulnerability‑remediation workflows.

The technical fix (bounding subrequest size to MAX_RW_COUNT) has been applied upstream and distributed through vendor/kernel updates. The operational task now is discovery, prioritization, and timely patching across all Linux artifacts in your environment — not a blind belief that Azure Linux’s attestation implies exclusivity for Microsoft products.

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In short: Azure Linux is the only Microsoft product Microsoft has publicly attested as including the vulnerable cachefiles code for CVE‑2024‑46748, but it is not the only plausible carrier — any Microsoft image or kernel build that includes the cachefiles subsystem could be affected until Microsoft attests otherwise or you verify the artifact yourself. Act accordingly.

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Source: MSRC Security Update Guide - Microsoft Security Response Center