# CVE-2026-19026 — The HDF Group HDF5

> As of 2026-08-06, CVE-2026-19026 is a Medium-severity (band derived from the CVSS v4.0 score, not stated by the CNA) vulnerability in The HDF Group HDF5, CVSS v4.0 6.8, EPSS 0.1% (2.7th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-19026 as of 2026-08-06; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-08-06

## What is CVE-2026-19026?

H5Z__filter_nbit in H5Znbit.c in HDF5 through 2.3.0 dereferences cd_values[0] through cd_values[4] without validating that cd_values is non-NULL or that cd_nelmts is at least 5, the fixed size of the filter's header. This allows attackers to cause a denial of service via a crafted HDF5 file that stores the N-Bit filter pipeline message with zero client-data values, opened and read via H5Dread, e.g. by the h5ls or h5repack tools.

The record classifies CVE-2026-19026 under weakness classes [CWE-476](https://intel.threadlinqs.com/cwe/CWE-476), [CWE-1284](https://intel.threadlinqs.com/cwe/CWE-1284). 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 61 days ago.

## Severity and exploitation probability

- **CVSS v4.0 base score:** 6.8 — Medium (derived from score) (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **EPSS (FIRST):** 0.1% probability of exploitation in the next 30 days, higher than 2.7% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 3.5/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-08-05, last modified 2026-08-06

## Is CVE-2026-19026 being exploited?

It currently carries a trending score of 30 in the Threadlinqs vulnerability feed.

## Affected products and versions

- **The HDF Group**: HDF5

## How to fix CVE-2026-19026

No vendor patch reference has been recorded for CVE-2026-19026 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-19026

No threat campaign in the Threadlinqs corpus currently references CVE-2026-19026, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-08-06.

**Other references**

- [github.com](https://github.com/HDFGroup/hdf5/pull/6497)
- [github.com (6489)](https://github.com/HDFGroup/hdf5/issues/6489)
- [github.com (6492)](https://github.com/HDFGroup/hdf5/issues/6492)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-19026
Full detection coverage and IOCs for threats exploiting CVE-2026-19026 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp