---
id: "CVE-2026-120755"
kind: "vulnerability"
aliases: ["CVE-2026-120755"]
title: "HDF5: crafted szip chunk causes out-of-bounds read and crash"
severity: "medium"
cvss: 4.7
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["hdf5", "libaec", "package", "python", "scientific-computing", "szip"]
not_affected_if: ["no-szip-support", "trusted-files-only"]
published_at: "2026-11-03T16:17:22+00:00"
first_seen_at: "2026-11-03T16:21:42+00:00"
updated_at: "2026-11-03T16:24:22+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-120755", "first_seen_at": "2026-11-03T16:21:42+00:00"}]
---

# HDF5: crafted szip chunk causes out-of-bounds read and crash

HDF5 through 2.2.0 subtracts a 4-byte header from a szip chunk length without checking the chunk is at least 4 bytes, so a truncated chunk wraps the length and the decompressor reads past the buffer. An attacker who gets a user or application to open a crafted HDF5 file can cause a denial of service.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check whether the HDF5 build includes szip support (libaec or szip library) and what HDF5 version is installed.
- Confirm the installed HDF5 version is `2.2.0` or earlier.

## Timeline

- 2026-11-03T16:21:42+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-120755

## From the sources

HDF5 through 2.2.0 contains an out-of-bounds read vulnerability in H5Z__filter_szip() in src/H5Zszip.c. When decoding a szip-compressed chunk, the function subtracts the 4-byte uncompressed-length header from the chunk length without first verifying that the chunk is at least 4 bytes long. A truncated or corrupted chunk shorter than the header causes the length calculation to wrap around to a very large value, and the decompressor reads far past the end of the chunk buffer. An attacker who can get a user or application to read a dataset from a crafted HDF5 file can cause a denial of service. Only builds with szip support (libaec or the szip library) are affected.

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