CVE-2026-120756

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CVE-2026-120756

Summary: Heap Buffer Over-read via Malformed Message Size in HDF5's H5O__chunk_deserialize

Details: 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.

References: https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/120xxx/CVE-2026-120756.json, https://nvd.nist.gov/vuln/detail/CVE-2026-120756, https://github.com/HDFGroup/hdf5/issues/6401, https://github.com/HDFGroup/hdf5/pull/6589