CVE-2024-7883: LLVM TrustZone-M Leak and Azure Linux Attestation

CVE-2024-7883 is a low-severity but meaningful LLVM/Clang compiler issue that can leak a small slice of a Cortex‑M Secure stack into Non‑secure state via floating‑point registers when certain Arm Cortex‑M Security Extensions (CMSE) calling patterns occur — and while Microsoft’s MSRC has attested that Azure Linux includes the implicated open‑source component, that attestation is a product‑scoped inventory statement, not a technical proof that no other Microsoft product could ever include the same library or be potentially affected.

Background / Overview​

CVE‑2024‑7883 was assigned to a compiler‑generated code pattern affecting Arm Cortex‑M with the CMSE (TrustZone‑M) extension: when a Secure→Non‑secure call returns a floating‑point value and that floating‑point is the first FP use since entering Secure state, residual Secure stack data may be left in floating‑point registers and thus be readable from Non‑secure code. The issue is tied to code produced by LLVM/Clang toolchains rather than a hardware design flaw in Cortex‑M silicon. Public vulnerability databases (NVD, OSV and leading distribution trackers) document the defect and classify it as confidentiality‑impacting with a low CVSS score. Why this matters in practice: the vulnerability is relevant to embedded firmware and development toolchains that build TrustZone‑M binaries using affected LLVM releases. For most server, desktop, and general cloud workloads the practical exposure is small; for firmware, IoT devices, and any supply‑chain that builds secure‑world code with vulnerable LLVM builds, the issue is worth immediate attention. Distribution trackers (Ubuntu, Debian, SUSE) and ecosystem dashboards provide package‑level status for affected llvm/clang packages — that is where most remediation effort will be focused.

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What Microsoft actually said — unpacking the MSRC wording​

Microsoft’s Security Response Center (MSRC) CVE pages use short, machine‑friendly FAQ lines to answer the common inventory question: “Is Azure Linux the only Microsoft product that includes this open‑source library and is therefore potentially affected by this vulnerability?” The answer MSRC publishes is intentionally conservative and operational: it affirms that Azure Linux includes the relevant open‑source component and is therefore potentially affected, and it notes Microsoft began publishing CSAF/VEX attestations starting in October 2025 and will update the CVE if additional Microsoft products are identified as carriers. That phrasing and programmatic rollout is deliberate. A plain reading of Microsoft’s statement yields two facts:

• Microsoft has completed an inventory for the Azure Linux product family and found the implicated component there (an authoritative positive attestation for Azure Linux).
• Microsoft is running a phased VEX/CSAF rollout and will update the product mapping if other Microsoft artifacts are later verified to ship the same upstream code.

Those two facts are helpful but they do not equate to a proof of exclusivity. Multiple independent analyses and community explainers make the same operational point: a product‑level attestation reduces ambiguity for the named product, but absence of attestation for other products is not the same as an authoritative statement that those products are clean.

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Technical summary of CVE‑2024‑7883​

• Affected component: compiler‑generated code (LLVM/Clang) for Arm Cortex‑M using CMSE.
• Root cause: floating‑point registers may retain Secure stack contents across a Secure→Non‑secure return when the callee’s FP use is the first since entering Secure state, allowing a limited read of Secure stack material from Non‑secure code.
• Scope: code produced by affected LLVM toolchains targeting TrustZone‑M; the issue is not a generic ARM CPU vulnerability but a code‑generation/regeneration pattern in certain LLVM releases.
• Impact: confidentiality (small amount of Secure stack disclosure). Attack complexity is non‑trivial and often requires local or supply‑chain conditions; public scoring places the issue at low to medium severity depending on scoring method.

Practical implication: system images, SDKs, firmware toolchains, or development environments that package or distribute affected LLVM versions are the places to patch. For embedded device owners, rebuilds with a fixed compiler or a compiler patch that clears FP registers on the Secure→Non‑secure boundary are the definitive remedy.

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Is Azure Linux the only Microsoft product that includes the library?​

Short answer: No — not necessarily. Azure Linux is the only Microsoft product MSRC has publicly attested so far to include the implicated open‑source library, but that attestation is an inventory statement for Azure Linux rather than proof that other Microsoft SKUs cannot carry the same upstream component. Microsoft explicitly committed to expand its machine‑readable VEX/CSAF attestations beyond Azure Linux as its inventory work proceeds. Treat the Azure Linux attestation as a confirmed, machine‑readable signal for that product; treat other Microsoft products as unverified until proven otherwise. Why that nuance is important:

• Microsoft ships many distinct artifacts — Linux distro images, WSL2 kernels, Azure VM images, container base images, Marketplace appliances, build/CI images, and developer tooling bundles. Each artifact is a build‑time product that can include or omit specific libraries and toolchains based on package choices and configuration.
• The same upstream source (for example an LLVM release) can appear in multiple Microsoft artifacts or nowhere outside Azure Linux, depending on what packages Microsoft included in each product. A single product attestation does not cover those other artifacts by default.
• Microsoft’s VEX rollout intentionally started with Azure Linux (a high‑value, cloud‑hosted Linux derivative), then plans to expand, which means their public attestations will appear in waves.

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Which Microsoft product types could plausibly carry the vulnerable component?​

The following Microsoft artifacts are plausible candidates to inspect, depending on how they are built and what packages are included:

• Azure Linux images (confirmed attestation).
• Microsoft‑published container images or curated developer images that include llvm/clang toolchains (for example images used in CI or packaged for developers).
• Windows Subsystem for Linux (WSL2) kernels and userland images: WSL user distributions or preinstalled developer toolsets can include LLVM/Clang packages; the WSL kernel itself is less likely to be the carrier for a compiler bug, but WSL distributions may ship vulnerable toolchain packages. Whether a particular WSL instance includes LLVM depends on the distro image and packages chosen.
• Azure Marketplace images or partner appliances that ship a specific Linux distribution or a preconfigured SDK stack that includes LLVM.
• Microsoft‑maintained developer VMs, build images used in Microsoft‑hosted CI (GitHub Actions runners or Azure DevOps hosted images), or other tooling images that include an LLVM toolchain.
• Specialized services (for example, Azure IoT device SDK images or prebuilt firmware build environments Microsoft may publish).

For many of these artifact categories the presence of the vulnerable component is conditional — it depends on whether the artifact includes an LLVM toolchain package and which version. This is why Microsoft’s product‑by‑product attestations are necessary for deterministic triage.

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Evidence and independent verification​

Key public validators for what the vulnerability is and how it behaves include:

• NVD / NIST CVE page for CVE‑2024‑7883 (technical description and metadata).
• Distribution vulnerability trackers (Debian, Ubuntu, SUSE) that catalog affected llvm packages and note remediation status (important because most real‑world remediation will happen by updating packaged llvm/clang in distributions).
• OSV / AVD / Rapid7 listings that aggregate the data and show downstream impact and package mappings.

Microsoft’s MSRC representations (CVE pages and the MSRC blog announcing the VEX/CSAF rollout) document their inventory approach and explicitly show Azure Linux as a “Known Affected” or “Potentially Affected” product for the kinds of third‑party CVEs they have scanned so far. Those pages are the authoritative signal from Microsoft for Microsoft‑owned images. Cross‑verification principle: For any product you run, correlate the package or binary version against the upstream CVE commit or fixed LLVM release, not just the high‑level CVE text. Distribution changelogs and package metadata map the fix‑commits into specific Debian/Ubuntu/SUSE package versions; use those concrete package versions to confirm a given image is patched.

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Practical guidance for administrators and developers​

If you run or manage Microsoft‑supplied artifacts, follow these pragmatic steps to verify exposure and remediate:

• Inventory artifacts:
• List Microsoft images and artifacts you run: Azure Linux instances, Azure Marketplace images, WSL distributions, container base images, build/CI images (GitHub Actions runners, Azure DevOps hosted agents).
• For each artifact, identify whether llvm/clang packages are installed or available.
• Map package versions to fixed releases:
• Check your installed clang/llvm package version and compare it with the CVE‑tracking pages (NVD, OSV, Ubuntu/Debian advisories) to determine if that package version is flagged vulnerable. Distribution trackers list specific package numbers and fixed versions.
• For firmware and embedded builds:
• Ensure toolchains that cross‑compile TrustZone‑M images use patched LLVM toolchains or vendor‑supplied toolchains that contain the compiler fix.
• Consider rebuilding firmware with an updated toolchain or applying compiler flags that clear FP state on Secure→Non‑secure transitions where applicable.
• Monitor Microsoft’s VEX/CSAF feed:
• Microsoft’s VEX/CSAF feed is intended to deliver machine‑readable attestations about which Microsoft products are Known Affected, Not Affected, or Fixed. Monitor the feed for updates beyond Azure Linux — Microsoft promised to expand its attestations as inventory work continues.
• Treat MSRC product attestations as authoritative for named artifacts, and treat the absence of attestation elsewhere as “not yet validated” rather than “safe.”
• If you depend on other Microsoft artifacts (WSL2 default images, Marketplace images, hosted build agents), actively verify those artifact contents rather than assuming they are excluded from the risk.
• Log and detect:
• The vulnerability itself is a confidentiality disclosure of a small stack area; detection by runtime logs is unlikely. Focus defensive controls on supply‑chain hygiene: pinned toolchain versions, reproducible builds, and CI policies that prevent the use of unapproved compiler packages in production firmware builds.

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Strengths and limitations of Microsoft’s VEX/CSAF approach​

Strengths

• Machine‑readable attestations reduce false positives and accelerate triage for customers who run the specified Microsoft products (start with Azure Linux). This is a pragmatic improvement over ambiguous textual advisories.
• The phased rollout allows Microsoft to validate attestations before scaling to larger product sets, which reduces mislabeling risk and operational noise.

Limitations and risks

• Phased coverage necessarily introduces a time window during which only a subset of Microsoft’s product portfolio is attested. Customers running other Microsoft artifacts must perform their own artifact‑level inventory until Microsoft’s VEX coverage is complete.
• The attestation model depends on accurate build‑time artifact inventories; any bug in inventory tooling or missed artifacts (for example, partner Marketplace images or older build images still in use) can leave coverage gaps.
• For compiler toolchain CVEs like CVE‑2024‑7883, the real risk often lives in developer tooling images, CI runners, or firmware build systems — items that may not be covered by a product attestation focused initially on cloud images.

Because of these limitations, security teams should combine Microsoft’s VEX attestations with their own artifact inspections and supply‑chain controls.

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When to escalate and what to ask Microsoft (if you are a customer)​

If you operate environments that depend on Microsoft‑provided artifacts and you need a deterministic answer for this CVE beyond Azure Linux, escalate with the following requests:

• Ask for artifact‑level attestations for the specific image or SKU you run (for example: “Do your Windows‑hosted GitHub Actions runners include llvm‑13 package X?”).
• Request confirmation of the exact package names and versions Microsoft shipped in the artifact you use.
• If you run custom Marketplace appliances, ask the vendor (or Microsoft, if it published the image) to confirm whether the image contains the vulnerable llvm/clang version.

Microsoft’s public posture commits to updating the CVE/VEX record if additional Microsoft products are found to ship the affected component; use that promise to request timely attestations for your high‑value artifacts.

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Conclusion​

CVE‑2024‑7883 is a compiler‑generated secrecy leak that matters most for TrustZone‑M firmware and any supply chains that build Secure world images using vulnerable LLVM toolchains. Microsoft’s MSRC has responsibly published a product‑level attestation that Azure Linux includes the implicated open‑source component and is therefore potentially affected, and Microsoft has committed to publishing machine‑readable VEX/CSAF attestations and to expanding product mappings over time. That attestation is authoritative for Azure Linux, but it is not a blanket technical guarantee that no other Microsoft product could carry the same vulnerable component — artifact‑level verification remains necessary for other images (WSL distributions, Marketplace images, hosted build images, container base images, and curated developer images).
Operational advice in short:

• Treat MSRC’s Azure Linux attestation as a confirmed signal and patch Azure Linux images you control.
• Inventory and check your other Microsoft artifacts (WSL, marketplace images, CI/build images) for llvm/clang versions and map them to fixed package versions reported by distributions and NVD.
• Monitor Microsoft’s VEX/CSAF feed for updates and request direct attestations for any high‑value Microsoft artifact that your organization depends on.

Where certainty is required — for example in regulated device production or in embedded firmware supply chains — the only defensible posture is to perform your own artifact verification or to require explicit attestations from the artifact supplier; Microsoft’s product attestation is a crucial help, but it is only one piece of the end‑to‑end supply‑chain assurance picture.

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Source: MSRC Security Update Guide - Microsoft Security Response Center