CVE-2025-2308: HDF5 Scale Offset Overflow and Azure Linux Attestation

A heap‑based buffer overflow has been reported in the HDF5 library’s Scale‑Offset filter (function H5Z__scaleoffset_decompress_one_byte) and cataloged as CVE‑2025‑2308 — a defect that affects HDF5 1.14.6 and can produce a one‑byte out‑of‑bounds write during decompression of Scale‑Offset encoded data. Multiple vulnerability trackers and distribution advisories confirm the vulnerable upstream release and the existence of a public proof‑of‑concept, and Microsoft’s Security Response Center (MSRC) has publicly attested that Azure Linux includes this open‑source library and is therefore potentially affected; however, that attestation is product‑scoped and does not prove that other Microsoft artifacts are free from the vulnerable HDF5 runtime.

---

Background​

HDF5 (Hierarchical Data Format version 5) is a C library and binary file format widely used in scientific computing, machine learning pipelines, imaging, and other data‑heavy workloads. The library exposes a set of filters for compressing and encoding dataset chunks; the Scale‑Offset filter is one such filter that performs compact numeric storage by scaling and offsetting values during compression and decompression.
The flaw tracked as CVE‑2025‑2308 is a heap‑based buffer overflow in the Scale‑Offset decompression path — specifically the H5Z__scaleoffset_decompress_one_byte routine — that can write one byte past a heap allocation when presented with crafted Scale‑Offset data. The NVD, Debian and Ubuntu advisories and several third‑party vulnerability databases record the vulnerability and identify HDF5 1.14.6 as the canonical affected release. Why this matters operationally: any service, tool, or container that links the vulnerable HDF5 runtime and processes untrusted .h5 files (uploads, automated ingestion, preview/thumbnail generation, conversion tools, or user‑facing utilities) can be forced to crash or corrupt memory by a crafted file. In server‑side ingestion scenarios, that crash can be triggered remotely by uploading the malicious file to the service. Several downstream distributions and packagers have catalogued the vulnerability and begun triage; however, timelines for fixed packages vary and some distributions have marked packages as “needs evaluation” or “postponed” pending upstream/backport decisions.

---

The Microsoft attestation: what it says and what it does not​

Microsoft’s published guidance for the CVE contains a short, repetitive FAQ answer that has been included on several MSRC product CVE pages: essentially, “Azure Linux includes this open‑source library and is therefore potentially affected by this vulnerability.” That statement is a deliberate, machine‑readable attestation tied to Microsoft’s rollout of CSAF/VEX artifact inventory outputs; it signals that Microsoft has completed the inventory for the Azure Linux distribution and verified that component X (HDF5) is present in that product family. Microsoft also states it began publishing CSAF/VEX attestations in October 2025 and “If impact to additional products is identified, we will update the CVE to reflect this.” This phrasing is procedural: authoritative for the named product (Azure Linux), not an exclusive denial for all Microsoft offerings. Two important, practically relevant translations of Microsoft’s wording:

• Affirmative for Azure Linux: Treat Azure Linux (the Azure‑maintained Linux distribution images) as in scope and subject to remediation, because Microsoft has explicitly attested that those images include the vulnerable HDF5 component.
• Not exhaustive for Microsoft: Absence of a similar attestation for other Microsoft products or images is not evidence those products are unaffected — it simply means those artifacts have not yet been mapped or attested in MSRC’s CSAF/VEX inventory process.

This distinction matters because Microsoft publishes many different Linux artifacts, kernels, images and container assets (Azure Marketplace images, MCR base images, AKS node images, Azure Machine Learning base images, WSL kernels, prebuilt containers, etc., and the presence of libhdf5 or language bindings is a per‑artifact build‑time property. Until a VEX/CSAF attestation declares a product “not affected,” defenders should treat un‑attested Microsoft artifacts as unverified with respect to the component.

---

Technical snapshot: CVE‑2025‑2308 (Scale‑Offset filter overflow)​

What the bug does​

• The bug occurs while decompressing data encoded with the Scale‑Offset filter. In the decompression routine the code can attempt to read or write one byte beyond a heap buffer when input values (length fields, control bytes, or encoded ranges) are malformed or adversarially crafted.
• The practical result is heap corruption and reproducible crashes under sanitizer builds; PoC artifacts have been published and reproduced by multiple maintainers and trackers.

Affected upstream versions​

• Canonical upstream affected release: HDF5 1.14.6 (this is the version many trackers and vendors reference as containing the vulnerable code). Downstream packages and bundles that include 1.14.6 (or an unpatched fork) are in scope.

Typical attack vectors​

• Server‑side ingestion, preview/thumbnailing, or conversion services that accept user uploads of .h5 files can be remotely triggered by an attacker uploading a crafted file.
• Desktop applications or command‑line tools require attacker control or social engineering to get a user to open the crafted file.
• Statically linked applications and container images that bundle the vulnerable runtime require rebuilds to remediate.

Immediate impact profile​

• Availability: High — reproducible crashes and DoS are the most certain outcome.
• Integrity: Possible — heap corruption can cause data corruption in long‑running processes.
• Confidentiality: Lower likelihood — overflow is a write primitive; memory disclosure would be secondary and environment dependent.
• RCE: Theoretical/speculative — turning a one‑byte heap overwrite into reliable remote code execution depends heavily on allocator behavior, ASLR, hardened allocators and additional primitives. Public advisories caution that RCE is not trivial and has not been widely demonstrated.

Cross‑check: these technical assertions are consistent across NVD, Debian and Ubuntu trackers and independent vulnerability feeds. For example, NVD records the same affected function and the local‑attack vector mapping, and distribution trackers list the component and package status for their releases.

---

Is Azure Linux the only Microsoft product that could be affected?​

Short answer: No — Azure Linux is the only Microsoft product Microsoft has publicly attested, so far, to include the vulnerable HDF5 library; that attestation is authoritative for Azure Linux but does not guarantee other Microsoft products are free of the component. Treat non‑attested Microsoft artifacts as unverified until Microsoft’s CSAF/VEX inventory or an independent inspection shows otherwise. Why that matters operationally:

• Microsoft distributes multiple Linux‑related artifacts (kernels, Azure Marketplace images, base container images, WSL kernels, Azure ML/DSVM images). Any of those could embed libhdf5 or ship language bindings (h5py, R hdf5, conda packages).
• The presence of HDF5 in one Microsoft image does not imply presence in all Microsoft images — each artifact has its own build and packaging pipeline.
• Microsoft’s CSAF/VEX rollout is phased; they started with Azure Linux. Future attestations may expand the product set declared as affected or not affected.

Unverifiable claim flag: if a public statement asserts that no other Microsoft products are affected, that would be an unverifiable negative without full artifact inventory and would contradict MSRC’s own process. The correct reading of Microsoft’s messaging is inventory‑scoped, not universal.

---

Practical guidance for WindowsForum readers and administrators​

If you run Azure Linux images provided by Microsoft

• Treat those images as in scope and apply Microsoft’s updates for the Azure Linux product line as they are published.
• Subscribe to Microsoft’s CSAF/VEX feed or the MSRC update guide for automated alerts tied to the Azure Linux attestation.

If you run other Microsoft images, kernels or artifacts (examples: WSL2 kernels, Azure Marketplace images, AKS node images, Azure ML base images, MCR container images)

• Do not assume safety because Microsoft has only attested Azure Linux so far.
• Inventory each artifact for the presence of HDF5 and language bindings:
• For Linux images: check native packages (rpm/dpkg) and installed libs (rpm -qa | grep hdf5; dpkg -l | grep hdf5).
• For Python environments: check h5py and the HDF5 runtime version inside wheels or conda packages (python -c "import h5py; print(h5py.version.hdf5_version)").
• For container images: inspect image layers and package metadata or run an ephemeral container and query the package manager.
• If you find libhdf5 or a bundled HDF5 runtime, confirm the exact build and whether the packaged release includes the upstream fix (look for the upstream commit/PR SHA or vendor changelog).
• Prioritize patching or image replacement for artifacts that accept untrusted .h5 inputs (upload endpoints, preview/thumbnailing services, automated conversion pipelines).

Immediate mitigations when patching is not yet available

• Block untrusted .h5 uploads at the perimeter or quarantine incoming files for manual review before decoding.
• Run HDF5 processing workloads in strongly isolated sandboxes (dedicated containers, strict seccomp/AppArmor/SELinux policies, user namespaces).
• Limit the privileges of processes that handle uploaded files and separate preview/processing services into small, short‑lived workers to reduce blast radius.
• Monitor and alert on segmentation faults and crashes in HDF5‑related processes (core dumps, repeated worker crashes, sudden abnormal process exits).

Verification checklist for remediation

• Confirm the package or bundle contains an HDF5 build that references the upstream remediation commit(s) in its changelog or SBOM.
• For statically linked binaries or vendor appliances: rebuild or obtain a patched binary from the vendor.
• For containers: pull updated base images that explicitly document the patched HDF5 package or rebuild images after updating the package layer.

---

How to validate statements and vendor attestations​

• Use NVD, distribution trackers (Debian/Ubuntu), and high‑quality vulnerability databases to verify CVE metadata and PoC status. These sources confirm the vulnerable release and reproduceability.
• For Microsoft’s claim that “Azure Linux includes this open‑source library,” consult the MSRC product CVE page or an archived capture of that page: the MSRC FAQ language is the authoritative vendor attestation and has been archived and reproduced across multiple CVE pages. Treat that page as the canonical signal for Azure Linux.
• Confirm vendor packages and distribution backports by examining package changelogs and the specific upstream commit SHAs included in the vendor’s patched package — do not rely on version numbers alone because downstream backports or selective merges can differ between vendors. Several distribution trackers explicitly advise checking changelogs and commits.

---

Critical analysis: strengths, gaps, and risk tradeoffs​

Strengths in the current response

• Microsoft’s early adoption of CSAF/VEX and the public attestation for Azure Linux is positive — it provides deterministic, machine‑readable evidence for at least one product family and enables automation of triage and patch workflows for Azure Linux consumers. This level of transparency is operationally valuable.
• Upstream HDF Group and major distributions have accepted fixes or are in the process of packaging the remediations, and multiple vendors have public trackers that make mapping easier for defenders.

Gaps and practical risks

• The phased VEX/CSAF rollout creates short windows where artifacts outside the initial attestation remain unverified; defenders who rely on vendor attestations without additional artifact inspection may mistakenly assume safety for un‑attested images.
• HDF5’s ubiquity across languages and packaging ecosystems (native packages, Python wheels, conda, static linking) means the same vulnerable codepath can live in surprising places (CI images, analysis VMs, research appliances), complicating inventory.
• Public PoCs increase attacker lead time for DoS and may enable skilled exploiters to attempt escalation chains; modern mitigations reduce but do not eliminate that risk.

Operational advice: treat Microsoft’s Azure Linux attestation as one authoritative signal but combine it with artifact‑level inventory, SBOM inspection, and distribution changelog verification to reach a defensible remediation posture.

---

Conclusion​

CVE‑2025‑2308 is a realistic, demonstrable heap‑based overflow in the HDF5 Scale‑Offset decompression path that affects HDF5 1.14.6 and presents a clear denial‑of‑service and heap‑corruption risk for any software that decodes untrusted .h5 content. Microsoft’s public mapping that Azure Linux includes the implicated open‑source library is an important, machine‑readable attestation and should be acted upon by Azure Linux users; however, that attestation is deliberately product‑scoped and does not prove other Microsoft products are unaffected. Administrators must therefore combine Microsoft’s CSAF/VEX outputs with their own artifact inventory and verification steps — especially for any Microsoft‑distributed images, kernels or containers that might embed libhdf5, h5py or other HDF5 bindings. Patch where vendor updates are available, sandbox and quarantine untrusted inputs where patching lags, and verify vendor changelogs or upstream commit SHAs when declaring systems remediated.

---

Key quick actions (ranked)

• Patch Azure Linux images as Microsoft updates are released (highest priority for attested product).
• Inventory Microsoft images you run (WSL, Marketplace, AKS, MCR images) for libhdf5/h5py and treat non‑attested artifacts as unverified.
• Quarantine or block untrusted .h5 uploads where possible; sandbox processing tasks.
• Verify vendor package changelogs or SBOMs include the upstream fix commit before declaring devices remediated.

This approach balances the operational benefit of Microsoft’s transparency with the practical reality that inventory mapping is an ongoing process — treat attestations as authoritative for what they name, but perform artifact‑level verification for everything else.

---

Source: MSRC Security Update Guide - Microsoft Security Response Center