CVE-2026-19026: HDF5 Denial of Service Vulnerability

CVE-2026-19026 Overview

CVE-2026-19026 is a null pointer dereference vulnerability in the Hierarchical Data Format version 5 (HDF5) library through version 2.3.0. The flaw resides in the H5Z__filter_nbit function within H5Znbit.c, which dereferences cd_values[0] through cd_values[4] without validating that cd_values is non-NULL or that cd_nelmts is at least 5. Attackers can trigger a denial of service by supplying a crafted HDF5 file that stores the N-Bit filter pipeline message with zero client-data values. Common HDF5 tools such as h5ls and h5repack crash when opening and reading such files via H5Dread.

Critical Impact
Processing a malicious HDF5 file causes a null pointer dereference that terminates the application, disrupting data analysis workflows and automated pipelines that consume untrusted HDF5 input.

Affected Products

HDF5 library through version 2.3.0
Command-line utilities h5ls and h5repack
Downstream applications linking libhdf5 for scientific data processing

Discovery Timeline

2026-08-05 - CVE-2026-19026 published to NVD
2026-08-05 - Last updated in NVD database

Technical Details for CVE-2026-19026

Vulnerability Analysis

The HDF5 library applies data transformation filters during dataset I/O operations. The N-Bit filter compresses data by stripping unused bits from numeric types. The filter reads configuration parameters from a client-data array cd_values whose length is provided in cd_nelmts. The N-Bit filter's fixed header requires at least five elements.

When the library parses a dataset that declares the N-Bit filter with cd_nelmts set to zero, cd_values may be NULL or too short. The H5Z__filter_nbit function proceeds to read cd_values[0] through cd_values[4] without validating either condition. The resulting memory access dereferences a NULL or invalid pointer and terminates the process.

This weakness is tracked as [CWE-476] NULL Pointer Dereference. The impact is limited to availability; no memory corruption or code execution has been reported.

Root Cause

The filter callback trusts attacker-controlled metadata from the HDF5 file's filter pipeline message. The function assumes the caller has populated cd_values with the required five entries, but the file format allows a dataset to declare zero client-data values. Missing input validation on both the pointer and the element count triggers the fault.

Attack Vector

Exploitation requires the target to open a crafted HDF5 file with a vulnerable tool or application. User interaction is required, since the victim must invoke a program such as h5ls or h5repack, or a custom application calling H5Dread, on the malicious file. No authentication or network access is needed. Full technical context is available in the upstream reports at GitHub HDF5 Issue #6489, GitHub HDF5 Issue #6492, and GitHub HDF5 Pull Request #6497.

No verified exploit code is currently public. The vulnerability manifests when the filter callback executes against a dataset whose N-Bit filter header declares zero client-data values.

Detection Methods for CVE-2026-19026

Indicators of Compromise

Repeated crashes of h5ls, h5repack, or other HDF5-linked processes when handling files from untrusted sources.
Core dumps or segmentation faults referencing H5Z__filter_nbit in the crashing stack frame.
HDF5 files whose filter pipeline messages declare the N-Bit filter with a cd_nelmts value of zero.

Detection Strategies

Scan ingested HDF5 files for filter pipeline messages that specify the N-Bit filter identifier with fewer than five client-data values.
Instrument data-processing services to log HDF5 library errors and abnormal terminations tied to file parsing.
Correlate application crashes with file provenance to identify malicious uploads.

Monitoring Recommendations

Monitor batch jobs and scientific pipelines for unexpected exits when consuming external HDF5 datasets.
Track the installed HDF5 library version across build systems and container images against the fixed release.
Alert on repeated failures of file-conversion utilities that link libhdf5 in shared workflows.

How to Mitigate CVE-2026-19026

Immediate Actions Required

Inventory all systems, containers, and applications that ship or link HDF5 through version 2.3.0.
Restrict processing of HDF5 files to trusted sources until the patched library is deployed.
Sandbox HDF5 parsing in isolated processes so that crashes do not disrupt broader services.

Patch Information

The fix is tracked in GitHub HDF5 Pull Request #6497, which adds validation of cd_values and cd_nelmts before dereferencing filter parameters. Rebuild dependent applications against a patched HDF5 release once available and redistribute updated binaries and container images.

Workarounds

Reject or quarantine HDF5 files received from untrusted sources until systems are patched.
Run tools such as h5ls and h5repack under supervisors that isolate faults and restart on crash.
Pre-validate HDF5 files with a hardened parser that rejects N-Bit filter headers containing fewer than five client-data values.

bash

# Example: isolate HDF5 tool invocations and reject small N-Bit headers
timeout 30s firejail --quiet --net=none h5ls "$UNTRUSTED_FILE" \
  || echo "HDF5 parsing failed for $UNTRUSTED_FILE" >> /var/log/hdf5-parse.log