A critical use‑after‑free defect has been publicly disclosed in the HDF5 library: CVE‑2025‑2913 identifies a flaw in src/H5FL.c (function H5FL__blk_gc_list) that can dereference freed metadata under specific local conditions, creating a realistic denial‑of‑service and memory‑corruption risk for any software that embeds or links HDF5 versions up to 1.14.6.
HDF5 (Hierarchical Data Format version 5) is a widely used C library and on‑disk format for large, hierarchical scientific and engineering datasets. It is commonly linked into command‑line tools (h5dump, h5repack), scientific stacks, and server‑side ingestion pipelines that accept and process .h5 files. Because HDF5 is often included directly in application binaries (dynamically or statically), memory‑safety defects in the library can influence a broad range of consumers. CVE‑2025‑2913 was disclosed publicly on March 28, 2025 and subsequently cataloged in mainstream trackers. The upstream affected release is HDF5 up to 1.14.6; multiple vulnerability databases classify the issue as a use‑after‑free in H5FL__blk_gc_list that requires local access to exploit. Public advisories and distribution trackers indicate a proof‑of‑concept or exploit details have circulated.
Source: MSRC Security Update Guide - Microsoft Security Response Center
Background / Overview
HDF5 (Hierarchical Data Format version 5) is a widely used C library and on‑disk format for large, hierarchical scientific and engineering datasets. It is commonly linked into command‑line tools (h5dump, h5repack), scientific stacks, and server‑side ingestion pipelines that accept and process .h5 files. Because HDF5 is often included directly in application binaries (dynamically or statically), memory‑safety defects in the library can influence a broad range of consumers. CVE‑2025‑2913 was disclosed publicly on March 28, 2025 and subsequently cataloged in mainstream trackers. The upstream affected release is HDF5 up to 1.14.6; multiple vulnerability databases classify the issue as a use‑after‑free in H5FL__blk_gc_list that requires local access to exploit. Public advisories and distribution trackers indicate a proof‑of‑concept or exploit details have circulated. The technical problem: what H5FL__blk_gc_list does and why it fails
What the function is responsible for
- H5FL__blk_gc_list is part of the HDF5 free‑list / block management helpers in src/H5FL.c.
- The routine manipulates linked lists of block addresses (free blocks) during garbage collection or block reuse operations; it must carefully manage ownership and pointer aliasing between multiple list structures.
Root cause summary
Public technical summaries indicate the function fails to handle duplicate block addresses that can appear in multiple lists safely. When list entries alias the same block address, the code may free the underlying block and later access the same block pointer from another list without re‑validating it, producing a classic use‑after‑free (UAF) memory safety violation. The bug manifests when multiple list chunks reference identical block addresses and the function does not detect or canonicalize those duplicates before freeing.Why this matters in practice
- A UAF in a native C library embedded into user processes can produce crashes (availability loss), information leaks, or under certain allocator and layout conditions be escalated into more powerful memory corruption primitives. Many public writeups treat the immediate impact as denial‑of‑service and memory corruption first; claims of reliable remote code execution require further chaining and are not proven by the vulnerability summary alone.
Evidence, confirmation and cross‑checks
Multiple independent vulnerability trackers have recorded and summarized CVE‑2025‑2913, and the National Vulnerability Database lists the defect with an updated description pointing to H5FL__blk_gc_list and a use‑after‑free root cause. Debian’s security tracker and other distro feeds reproduce the same core diagnosis and reference upstream issue threads and commits that implement fixes. These independent confirmations increase confidence that the defect is real and the affected code path is correctly identified. At the same time, published severity scores vary: different CNAs and trackers assign CVSS scores ranging from low to medium/critical depending on their assessment matrix and whether they include exploit maturity. This distribution of scores is typical when an issue is local‑vector but has a practical impact on server‑side ingestion patterns. Treat public severity differences as a reflection of contextual risk models rather than contradictory facts.Exploit status and exploitability analysis
- Public feeds and several trackers note that exploit code or a proof‑of‑concept has been disclosed. The presence of a PoC materially reduces attacker lead time and increases operational urgency for exposed systems. However, reviewers also caution that an attacker needs local access and the specific HDF5 code path to be exercised for exploitation.
- Practical exploitability depends heavily on the runtime context:
- Is the vulnerable HDF5 library used in a service that automatically parses untrusted .h5 files (high risk)?
- Is HDF5 statically linked into binaries where swapping a shared library package won't remediate the binary (requires rebuilds)?
- What platform mitigations are present (ASLR, hardened allocators, PIE, RELRO)? These influence whether a UAF can be turned reliably into code execution.
- Verdict on RCE: no authoritative public analysis has demonstrated a trivial, reliable remote code execution chain from this specific UAF in the wild. Multiple reports emphasize availability and heap corruption as the principal, realistic outcomes. Treat RCE claims as unverified unless independent exploit writeups show a working RCE chain.
Who is affected
- Confirmed affected: HDF5 versions up to 1.14.6. If a vendor has backported the upstream fix into distribution packages, those package versions may be safe — check changelogs and vendor advisories for confirmation.
- Typical at‑risk deployments:
- Server‑side ingest and preview services that accept user uploads of .h5 files and process them automatically.
- Shared compute or HPC environments that run batch tools processing untrusted datasets.
- Binaries that statically link libhdf5 (embedded appliances, specialized tools). Replacing a shared package will not remediate statically linked executables.
- Lower‑risk scenarios:
- Systems that never parse HDF5 data or explicitly disable the affected allocator/GC path.
- Offline analysis on trusted data where input origin is controlled and audited.
Detection and telemetry: how to spot attacks or crashes
- Primary indicator: reproducible segmentation faults, SIGSEGVs, or crashes in processes that parse HDF5 files, particularly in tools like h5dump, h5repack, or custom conversion utilities that call into HDF5 internals. Correlate crash timestamps with recent file uploads or ingestion events.
- Secondary indicators:
- Repeated worker restarts or high rates of process churn in ingestion pools.
- Presence of known PoC files (file names, hashes) in uploaded content repositories.
- Application logs recording inconsistent free/list state if logging covers HDF5 internals (rare in production).
- For developers: enable AddressSanitizer/MemorySanitizer during testing and add targeted fuzz tests against block list and free‑list manipulation code paths. Defensive unit tests that exercise duplicate block address handling will catch regressions earlier.
Remediation and mitigation — practical playbook
Immediate priorities for defenders:- Inventory: locate all binaries, packages, container images and appliances that include HDF5. Search package managers, container registries, build artifacts and static binary lists for versions ≤ 1.14.6. Prioritize internet‑facing ingestion endpoints.
- Patch: apply vendor or upstream fixes where available. If your distribution has a package update that explicitly lists CVE‑2025‑2913 or references the upstream commit/PR, deploy it and restart affected services. Confirm the package changelog or vendor advisory includes the upstream commit ID.
- Rebuild statically linked binaries: for any tool or appliance that statically links libhdf5, you must rebuild the binary with the patched library and redeploy the rebuilt artifact. Replacing system shared libraries will not fix statically linked executables.
- Block or quarantine untrusted .h5 uploads and toggle automated processing off. Move file parsing into a queued, air‑gapped, or sandboxed worker where crashes are constrained.
- Sandbox HDF5 parsing processes with strict privileges, seccomp filters, resource limits (cgroups), and ephemeral containers so a crash or exploit cannot escalate across the host.
- Network controls: restrict who can upload or submit HDF5 files to ingestion endpoints; require authenticated uploads, and inspect files in a quarantine stage before allowing parsing.
- Monitoring: add high‑priority alerts for repeated worker restarts, SIGSEGV traces mentioning H5FL.c, and anomalous error rates during HDF5 decoding.
- Confirm the installed package or rebuilt binary contains the upstream patch/commit addressing H5FL__blk_gc_list (check vendor changelogs, PR/commit IDs, or package metadata).
- For static binaries, run a deterministic test that feeds the known PoC (in a safe lab) to the patched binary and confirm the crash no longer reproduces. Use isolated test rigs for PoC verification.
Developer guidance and hardening recommendations
- Add targeted unit tests and fuzz harnesses that exercise the free‑list/block GC behavior and explicitly test repeated / duplicate block entries to prevent regressions.
- Prefer dynamic linking in environments where you can centrally patch shared libraries; when static linking is necessary, maintain a clear rebuild plan and track upstream security advisories to rebuild quickly.
- Use modern memory‑safety tools during CI: AddressSanitizer to detect UAFs, MemorySanitizer to find uninitialized reads, and fuzzing to sweep serialization and allocator helpers. These techniques have found similar HDF5 issues historically.
- Consider least‑privilege wrappers: run third‑party converters and previewers under restricted users or ephemeral containers so that a compromised process cannot access sensitive host resources.
Risk assessment and operational recommendation
- Likelihood of exploitation in the wild: moderate — a PoC exists and HDF5 is widely used. The local attack vector lowers remote exposure but does not eliminate risk in cloud or shared ingestion pipelines where attackers can submit files.
- Impact if exploited: primarily availability and integrity (process crashes, heap corruption). Under favorable conditions and with additional chaining, memory corruption could be escalated toward code execution, but that requires further conditions and is not documented as trivial today.
- Business priority: treat servers and services that parse untrusted .h5 inputs as high priority for patching and mitigations. Developer workstations and isolated research nodes are medium priority but still warrant updates if they accept external files.
- Long tail: embedded appliances and vendor images that statically include HDF5 present the longest remediation tail — track vendor advisories and schedule rebuilds or firmware updates accordingly.
What remains uncertain — flagged claims and cautions
- Several trackers report different CVSS numbers (from low to medium/critical) and differing exploit maturity assessments. These differences reflect varying scoring methodologies and should not be conflated with conflicting root‑cause facts. Trust vendor advisories and the NVD for canonical descriptions, and use your own environment’s threat model to prioritize response.
- Public reports indicate an exploit or PoC has been disclosed; however, whether that PoC translates into reliable remote code execution across common deployment targets is not demonstrated in authoritative analysis. Treat RCE claims as unverified until multiple independent exploit writeups demonstrate it.
- Distribution packaging status varies: some distributions may postpone packaging or backport the fix differently. Administrators must verify that their platform’s package includes the exact upstream fixes rather than assuming a generic package upgrade is sufficient.
Practical timeline and next steps for administrators
- Immediately inventory HDF5 usage across hosts, containers, CI artifacts and images. Search for package versions ≤ 1.14.6 and mark internet‑facing ingestion services as top priority.
- Apply vendor or distribution updates that explicitly reference CVE‑2025‑2913 or upstream commit IDs. If no package is available, plan to rebuild static artifacts with patched source.
- While patching is in progress, isolate or sandbox HDF5‑processing services, disable automatic parsing of untrusted .h5 files, and enable aggressive crash monitoring.
- For security teams: collect any suspicious uploaded .h5 files, move them to a quarantined lab for analysis, and look for indicators such as repeated crash logs or presence of known PoC files.
- Post‑remediation: add fuzz tests and unit coverage for HDF5 block list code paths in your CI; consider integrating sanitizer builds into release pipelines for higher assurance.
Conclusion
CVE‑2025‑2913 is a concrete memory‑safety defect in HDF5’s block garbage collection helper that can produce use‑after‑free behavior when duplicate block addresses are mishandled. Multiple independent trackers, including the NVD and major distribution security feeds, corroborate the diagnosis and identify HDF5 ≤ 1.14.6 as affected. The presence of publicly disclosed PoC material raises urgency for environments that automatically parse untrusted .h5 files or statically embed HDF5. Immediate steps are straightforward: inventory, apply vendor patches or rebuild statically linked binaries, sandbox file processing, and enable crash monitoring. Longer‑term resilience requires improved test coverage, fuzzing and memory‑sanitizer integration to prevent regressions in critical serialization and allocator helpers.Source: MSRC Security Update Guide - Microsoft Security Response Center
