CVE-2025-2153: HDF5 Heap Overflow and Azure Linux Attestation

A critical heap‑based buffer overflow in the HDF5 library — tracked as CVE‑2025‑2153 and rooted in the H5SM_delete function in H5SM.c — has resurrected a familiar supply‑chain question: Microsoft’s advisory names Azure Linux as a carrier of the vulnerable open‑source code, but does that mean Azure Linux is the only Microsoft product that could be affected? The short, operationally important answer is: No — Azure Linux is the only Microsoft product Microsoft has publicly attested to include the vulnerable HDF5 component so far, but absence of an attestation is not proof that other Microsoft artifacts do not contain the library. Treat the Azure Linux attestation as authoritative for that product family, and treat every other Microsoft image, agent, or appliance as unverified until you confirm inventory and build details.

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Background / Overview​

HDF5 (Hierarchical Data Format v5) is a foundational binary container and C library used widely across scientific computing, data analytics, imaging stacks, and high‑performance workflows. The newly catalogued CVE‑2025‑2153 identifies a heap buffer overflow in the H5SM_delete routine of HDF5 v1.14.6, a weakness that public trackers and vendor advisories characterize as capable of causing crashes and memory corruption and — depending on runtime conditions — possibly enabling further exploitation. Public vulnerability databases and distribution trackers show HDF5 1.14.6 as the affected upstream release. Technically, the bug arises when the H5SM_delete code path performs unchecked or insufficiently guarded memory operations on heap allocations while processing certain shared‑metadata entries; malformed or deliberately crafted .h5 files that exercise those code paths can trigger writes beyond allocated buffers, producing heap corruption. The primary observed real‑world impact is denial‑of‑service and data corruption, while escalation to reliable remote code execution requires favorable allocator behavior and attack chaining. Public proof‑of‑concepts exist that reproduce crashes, increasing the urgency for patching and mitigations.

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What Microsoft actually published — and why it matters​

Microsoft’s public advisory for this vulnerability states: “Azure Linux includes this open‑source library and is therefore potentially affected by this vulnerability.” That statement is a product‑scoped attestation — essentially a machine‑readable, inventory‑level confirmation that Microsoft inspected Azure Linux images, found the implicated library, and categorized the product as potentially affected. Microsoft has also said it began publishing CSAF/VEX attestations in October 2025 and will update CVE records if additional Microsoft products are later identified as carriers of the same upstream library.
Why this matters in practice:

• A VEX/CSAF attestation is authoritative for the named product family — treat the named product (Azure Linux) as in‑scope and act accordingly.
• The attestation is not an exclusive claim; Microsoft did not and has not claimed that no other Microsoft products include the vulnerable library.
• Large vendors commonly publish attestations in phases. Microsoft started with Azure Linux as a logical place to run the inventory automation; other SKUs may be checked and attested later.

In short: the wording reflects Microsoft’s inventory progress, not a global denial of exposure across all Microsoft products and images.

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Technical snapshot: CVE‑2025‑2153 at a glance​

• Affected component: HDF5 (h5 File Handler), version 1.14.6.
• Vulnerable function: H5SM_delete (source file H5SM.c).
• Vulnerability class: heap‑based buffer overflow (write beyond heap allocation).
• Primary impact: availability (crashes/Denial‑of‑Service) and potential integrity loss (data corruption). Escalation to reliable RCE is environment‑dependent.
• Proof‑of‑concept: crash PoCs have been published in public repositories, increasing exploitability risk for unpatched deployments.

Multiple vulnerability databases (NVD, Debian security tracker, third‑party aggregators) catalog the CVE and map it to upstream commits or GitHub issues where fixes were discussed, demonstrating cross‑vendor awareness and coordination.

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Why Azure Linux’s attestation is useful — and why it’s not the whole picture​

Microsoft’s attestation for Azure Linux is valuable because it provides deterministic, machine‑readable evidence for one explicit product family. If you run Azure Linux images provided by Microsoft, that attestation enables automation: you can mark those images as in‑scope for immediate remediation, track vendor KBs, and prioritize patching or image replacement.
However, three operational caveats are critical:

• Attestations are per‑artifact, not per‑vendor. A vendor can have many different images, kernels, containers and appliances; inclusion of a vulnerable library is a property of each artifact’s build configuration. Presence in one image does not mean universal presence in others.
• Static linking and bundled artifacts complicate detection. Applications may embed HDF5 statically (for example, in vendor appliances, Python wheels, conda packages, or proprietary binaries), making simple package‑manager checks insufficient. Those artifacts require binary inspection, SBOM analysis, or rebuilds to remediate.
• Marketplace images, partner appliances, and third‑party vendors can introduce exposure into your Azure tenancy even if Microsoft’s own attestations are limited to Azure Linux images. Microsoft’s attestation lists the product(s) they checked — it does not auto-validate third‑party Marketplace images.

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Which Microsoft products could include HDF5 (and why you should check them)​

Any Microsoft artifact that contains a Linux userland or ships common scientific toolchains might include HDF5. Plausible carriers include:

• Azure VM images and Marketplace images (beyond Azure Linux). Vendors publish many curated images (Data Science VMs, HPC images, AI/ML AMIs) that may include HDF5 packages.
• Container base images published or curated by Microsoft in Azure Container Registry or marketplace-enabled registries. These images are commonly used in cloud workloads and may include the hdf5 library in package lists.
• Windows Subsystem for Linux (WSL) distributions and kernels when they include userland packages that use HDF5 (for example, conda environments). WSL images are often assembled from common distro packages and can carry the same vulnerabilities.
• Azure Data Science and AI platform images (machine learning images with Python/R stacks), which frequently include HDF5 bindings used by NumPy, h5py, MATLAB exporters, or other scientific stacks.
• Microsoft‑distributed agents or appliances (for backups, telemetry, ingestion) that run a Linux rootfs and ship bundled binaries. These can include statically‑linked versions of libraries.

The operational implications are simple: if you run any of these artifacts, you must independently verify whether HDF5 1.14.6 (or another vulnerable build) is present.

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Practical detection: how to verify exposure in your estate​

Inventory and verification are the only reliable ways to know whether a given Microsoft product or artifact is affected. Use the following prioritized checklist to detect HDF5 carriers:

• Quick package checks (for package‑managed images):
• Debian/Ubuntu: dpkg -l | grep -i hdf5
• RPM systems: rpm -qa | grep -i hdf5
• Confirm installed version numbers against the vendor advisory.
• Container image scanning:
• Run container scanners that inspect package manifests and filesystem layers (Trivy, Clair, Anchore).
• Inspect /usr/lib /usr/local/lib /opt directories for libhdf5 files and version metadata.
• Python / Conda / R packages:
• Check pip/conda environments for h5py, pytables or other bindings that may bundle HDF5 wheels.
• Inspect binary wheels (manylinux) for embedded libhdf5 via strings or auditwheel.
• Static binary and appliance inspection:
• Use ldd on binaries that might use HDF5 to find dynamic links; for statically‑linked binaries use strings and symbol grep to search for HDF5 symbols (H5SM, H5F prefixes).
• Extract filesystem images (VM disk, container layers, or Marketplace image tarballs) and run grep against known HDF5 file headers or library filenames.
• SBOM and VEX:
• Use provided SBOMs (if available) or request CSAF/VEX outputs from vendors. Microsoft’s published VEX entries are authoritative for the specific artifacts they cover; use them to short‑circuit verification for those images.
• Runtime telemetry:
• Search for crashes or core dumps referencing h5 or HDF5 symbols; monitor logs from ingestion pipelines that process .h5 files for anomalous exits.

If you find HDF5 v1.14.6 present in any artifact you manage, treat that artifact as vulnerable until patched or rebuilt.

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Mitigation and remediation playbook​

Priority actions for defenders and admins:

• Patch first where vendor packages exist. If a vendor or upstream release explicitly contains the HDF5 fix (for example, a new point release or distro package that references the upstream fix commit), apply it and rebuild or redeploy images. Confirm changelog entries or commit IDs in the package metadata.
• If no vendor package is available:
• Rebuild the HDF5 library from source incorporating the upstream fix/commit and rebuild downstream artifacts that statically link HDF5 (Python wheels, containers, appliances).
• Prefer an official patched release (or a confirmed vendor backport) when available; if forced to build a custom patch, document and test it carefully.
• Short‑term mitigations until patched images are available:
• Block ingestion of untrusted .h5 files where possible (disable automatic uploads or require authentication/validation).
• Sandbox or isolate HDF5‑processing services (unprivileged containers, seccomp, AppArmor/SELinux) to limit blast radius.
• Disable or restrict services that auto‑process .h5 inputs (thumbnailers, preview engines, conversion daemons) on public‑facing endpoints.
• Long term: implement SBOM generation and aggressive supply‑chain hygiene so future attestations and vulnerabilities can be mapped to running artifacts quickly.

A minimal prioritized remediation checklist:

• Identify all Azure Linux images you run and apply Microsoft’s recommended updates for those images immediately.
• Inventory all other Microsoft images and artifacts (Marketplace images, Data Science images, WSL distributions, container base images). Verify presence of HDF5.
• Patch or rebuild any artifact that embeds vulnerable HDF5 (static or dynamic linking).
• Apply operational mitigations (sandboxing, upload controls, monitoring) until fixes are fully deployed.

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Risk assessment — how bad is this, really?​

Several independent sources converge on the following risk profile:

• Exploitability: Public PoCs exist that trigger crashes; turning those crashes into reliable remote code execution is non‑trivial but possible under favorable conditions (allocator behavior, deterministic heap layout, exploitation mitigations absent). The principal, immediate risk is Denial‑of‑Service and data corruption.
• Exposure surface: Systems that accept untrusted .h5 files and feed them into automated ingestion or conversion pipelines are the highest risk. Desktop apps where users open files interactively pose lower mass‑exploitation risk but remain attack vectors for targeted social engineering. Server‑side ingestion and thumbnailing services are the most consequential.
• Likelihood: The presence of PoC material reduces the time window for exploit attempts; EPSS/early exploit metrics vary, but distribution scanners and vendor trackers have flagged this vulnerability as important, so rapid patching is prudent.
• Microsoft product scope: Microsoft’s Azure Linux attestation reduces uncertainty for that product — administrators running those images can prioritize remediation with high confidence. But for other Microsoft SKUs, you must assume unverified exposure until inventory confirms otherwise.

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Why vendor attestations (CSAF / VEX) are progress — and their limits​

Microsoft’s CSAF/VEX publishing is an operational improvement: it provides machine‑readable, authoritative mappings between CVEs and specific Microsoft artifacts. That reduces triage friction for Azure Linux customers and enables automation of remediation workflows. However, VEX feeds are only as useful as their coverage. Vendors with large artifact footprints typically publish in phases; the absence of a VEX attestation for a product does not prove that the product is unaffected. Use VEX as a positive signal when present and as a cue to perform direct verification when absent.

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Actionable checklist for WindowsForum readers (concise)​

• If you run Azure Linux images from Microsoft: follow Microsoft’s update guidance and apply the provided patches or image replacements immediately.
• For any other Microsoft‑supplied image or container: do not assume clearance — inventory and verify. Use package managers, SBOMs, and container scanners.
• For appliances, vendor images, and static binaries: inspect binaries for embedded HDF5 symbols and consider rebuilding with patched HDF5.
• Block or sandbox any service that automatically accepts and processes untrusted .h5 files until patched builds are in place.

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Conclusion​

CVE‑2025‑2153 is a real, actionable vulnerability in HDF5 1.14.6 that can crash or corrupt applications that process specially crafted .h5 files. Microsoft’s public statement that Azure Linux includes the implicated library and is therefore potentially affected is correct and useful — it is an authoritative, product‑level attestation for Azure Linux — but it is not a blanket statement that other Microsoft products are unaffected. Absence of a public attestation from Microsoft for other SKUs means those SKUs are unverified, not cleared. Defenders must therefore combine vendor attestations with active artifact inspection, SBOM analysis, and targeted mitigations (sandboxing, ingestion controls, rebuilds) to close exposure quickly. Prioritize Azure Linux images for remediation if you run them, but do not stop your visibility or scanning work at that boundary — comprehensive inventory and timely patching remain the only reliable defenses.

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Source: MSRC Security Update Guide - Microsoft Security Response Center