HDF5 CVE-2026-19027

Q: What is the CVSS score of CVE-2026-19027?

CVE-2026-19027 has a CVSS 4.0 base score of 6.9 (Medium). CVSS vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.1%.

EUVD-2026-53678 MEDIUM

Out-of-bounds Read (CWE-125)

2026-08-05 HDFG

GHSA-2pvh-qgr3-wp2r

Buffer Overflow Information Disclosure Hdf5 The Hdf Group

6.9

CVSS 4.0 · Vendor: HDFG

Severity by source

Vendor (HDFG) PRIMARY

6.9 MEDIUM

CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

vuln.today AI

6.1 MEDIUM

File must be locally opened by a user or tool (AV:L, UI:R); no privileges needed to deliver a file (PR:N); heap disclosure is limited (C:L) and crashes are reliable (A:H).

3.1 AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:H

4.0 AV:L/AC:L/AT:N/PR:N/UI:P/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N

SUSE

3.3 LOW

AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

Red Hat

5.6 MEDIUM

qualitative

Primary rating from Vendor (HDFG).

CVSS VectorVendor: HDFG

Attack Vector

Local

Attack Complexity

Low

Privileges Required

None

User Interaction

Scope

Lifecycle Timeline

Source Code Evidence Fetched

Aug 05, 2026 - 23:52 vuln.today

Analysis Generated

Aug 05, 2026 - 23:52 vuln.today

DescriptionCVE.org

The H5Z__nbit_decompress_one_byte, H5Z__nbit_decompress_one_nooptype, and H5Z__nbit_decompress_one_atomic functions in H5Znbit.c in HDF5 through 2.3.0 advance a read index into the compressed chunk buffer without bounding it against the buffer's actual size. This allows attackers to cause an out-of-bounds heap read, and in constrained cases disclosure of adjacent heap memory into decompressed dataset values, via a crafted HDF5 file whose N-Bit filter parameters describe more decompressed data than the stored compressed chunk actually contains, triggered via H5Dread, e.g. by the h5ls or h5repack tools.

AnalysisAI

Out-of-bounds heap read in HDF5's N-Bit filter decompression affects all versions through 2.3.0, allowing an attacker who can deliver a crafted HDF5 file to a user or automated pipeline to trigger application crashes and, in constrained cases, leak adjacent heap memory contents into decompressed dataset values. The three affected functions - H5Z__nbit_decompress_one_byte, H5Z__nbit_decompress_one_nooptype, and H5Z__nbit_decompress_one_atomic - advance a buffer read index without bounding it against the actual compressed chunk size, exploitable whenever H5Dread is invoked, including via common tools like h5ls and h5repack. No public exploit code has been identified at time of analysis, and this vulnerability is not listed in the CISA KEV catalog.

Technical ContextAI

HDF5 (Hierarchical Data Format version 5) is a data model and file format library used extensively in scientific computing, data science, and high-performance computing. The N-Bit filter (H5Znbit.c) is a dataset compression filter that packs integer or floating-point data into fewer bits to reduce storage. During decompression via H5Dread, the filter iterates over compressed chunk bytes using an index variable (j) and bit-length counter (buf_len), but the original code never compared j against the actual buffer size - it could read arbitrarily beyond the chunk boundary into adjacent heap memory. CWE-125 (Out-of-bounds Read) is the root cause: the filter trusted that the N-Bit filter parameters (cd_values) correctly described the data volume, without validating that the compressed chunk was large enough to satisfy those parameters. The fix in PR #6497 propagates a buffer_size argument through all three decompression functions, adds a H5Z_NBIT_PARMS_AVAIL bounds macro, and also hardens the cd_values NULL/length check (rejecting arrays shorter than the mandatory 5-element header). The same PR also fixes a related Fletcher32 filter integer underflow. Affected CPE: cpe:2.3:a:the_hdf_group:hdf5:*:*:*:*:*:*:*:*.

RemediationAI

Apply the upstream fix from GitHub PR #6497 (https://github.com/HDFGroup/hdf5/pull/6497), which adds buffer bounds validation throughout the N-Bit decompression path and hardens the cd_values parameter check. Note that this is a GitHub pull request and not a tagged release - a released patched version number was not independently confirmed from the available data; monitor the HDF Group release page and the referenced issues (#6489, #6492) for a formal release. As a compensating control where patching is not immediately possible, restrict the processing of externally sourced or untrusted HDF5 files: disable or sandbox tools such as h5ls and h5repack when operating on untrusted input, enforce file-origin allowlisting in data pipelines, and consider running HDF5 readers in isolated processes or containers with memory limits to contain crash impact. Disabling the N-Bit filter programmatically at the application layer (if dataset creation is under your control) eliminates the vulnerable code path entirely, though this is impractical for read-only consumer scenarios.