# CVE-2025-6856: HDF5 H5FL.c H5FL__reg_gc_list use after free

CVE-2025-6856 is fixed in hdf5 on 1 platform by DEBIAN-CVE-2025-6856 (version 2.1.0+repack-1), released June 29, 2025. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2025-6856
- Priority: High
- CVSS: 7.8 (high)
- EPSS: 0.0025
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 29, 2025
- Weakness: Use After Free
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-6856

## Description

A vulnerability, which was classified as problematic, was found in HDF5 1.14.6. Affected is the function H5FL__reg_gc_list of the file src/H5FL.c. The manipulation leads to use after free. Attacking locally is a requirement. The exploit has been disclosed to the public and may be used.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | hdf5 Debian 14 | 2.1.0+repack-1 | [DEBIAN-CVE-2025-6856](https://patchblox.com/security/data/fix/linux/debian-cve-2025-6856.md) | Jun 29, 2025 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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