CVE-2026-120756: Heap Buffer Over-read via Malformed Message Size in HDF5's H5O__chunk_deserialize

Vulnerability summary

CVE-2026-120756 is a medium (CVSS 6.1) Out-of-bounds Read vulnerability in hdfgroup hdf5. 1 public exploit is recorded.

Timeline

1. 03-11-2026
   PublishedVulnerability first disclosed.
2. 03-11-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-125Out-of-bounds ReadThe product reads data past the end, or before the beginning, of the intended buffer.