# CVE-2026-17574: The HDF Group HDF5 NULL pointer dereference in H5O__dtype_decode_helper

Source: https://junglewise.ai/threats/cve-2026-17574-the-hdf-group-hdf5-null-pointer-dereference-in-h5o-dtype-decode  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-27. Updated: 2026-07-27  
License: CC BY 4.0 with a link back

CVE-2026-17574 · Severity: info · CVSS 5.2 · Published 2026-07-27

HDF5 is a high-performance data management library used to store and organize large amounts of data. A vulnerability exists where processing a specially crafted HDF5 file can cause applications using the library to crash. This could lead to a denial-of-service, interrupting research or business operations that rely on processing these data files.

## Quick answers

**Is CVE-2026-17574 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-17574 being exploited in the wild.

**How severe is CVE-2026-17574?** Informational severity, with a CVSS score of 5.2, published 27 July 2026.

**Which products and versions are affected?** The HDF Group HDF5 <= 2.1.1.

**Is there a fix for CVE-2026-17574?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-17574 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-17574?** Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A NULL pointer dereference and reachable assertion vulnerability exists in HDF5's H5O__dtype_decode_helper() and H5T_set_loc() functions. The root cause is a failure to validate the 'vlen.type' field during the decoding of variable-length datatypes; if the field contains a value other than H5T_VLEN_SEQUENCE or H5T_VLEN_STRING, it triggers an assertion failure in debug builds or a segmentation fault in release builds. An attacker can exploit this by providing a malformed HDF5 file to an application that reads its attributes. A fix has been developed that adds validation checks during decoding and ensures file pointers are not NULL before processing.

## Affected products

- The HDF Group HDF5 <= 2.1.1

## Timeline

- 2026-07-27: disclosed
- 2026-07-27: advisory

## References

- [https://github.com/HDFGroup/hdf5/commit/3fa6ed6e9dfeebbc784e21d8c48e31e35a8042bc](https://github.com/HDFGroup/hdf5/commit/3fa6ed6e9dfeebbc784e21d8c48e31e35a8042bc)