---
id: CVE-2026-120756
title: >-
  Heap Buffer Over-read via Malformed Message Size in HDF5's
  H5O__chunk_deserialize
summary: >-
  HDF5 through 2.2.0 contains a heap buffer over-read vulnerability in
  H5O__chunk_deserialize() in src/H5Ocache.c. When decoding object header
  messages, the declared message size is checked against the end of the chunk
  image before the rem…
severity: low
cvss: 1.9
cvssVector: 'CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N/E:P'
cvssSource: cna
cwe:
  - CWE-125
vendor: The HDF Group
product: HDF5
affected:
  - HDF5 < 2.3.0
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-03T17:55:08.252551Z'
published: '2026-11-03'
updated: '2026-11-03'
sourceUpdated: '2026-11-03T17:55:20.773Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-120756'
references:
  - url: 'https://github.com/HDFGroup/hdf5/pull/6589'
  - url: 'https://github.com/HDFGroup/hdf5/issues/6401'
tags:
  - cve.org
epss: 0.00178
epssPercentile: 0.07462
ingestedAt: '2026-11-05T20:33:06.335Z'
---

## Overview

HDF5 through 2.2.0 contains a heap buffer over-read vulnerability in H5O__chunk_deserialize() in src/H5Ocache.c. When decoding object header messages, the declared message size is checked against the end of the chunk image before the remainder of the message header (flags, and for version 2 object headers, the optional creation index) has been decoded. Because the message body begins after these fields, a message can start up to four bytes further into the chunk than the size check accounts for. A crafted HDF5 file can declare a message size that passes the check but extends past the end of the chunk image, causing the message’s decode callback, for example H5O__mtime_new_decode() in src/H5Omtime.c, to read beyond the heap allocation. The flaw is reachable during H5Fopen() on a crafted file. An attacker who can get a user or application to open a malicious file can cause a denial of service or limited disclosure of process memory.

## Affected

- `HDF5 < 2.3.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.