Quick answers
- Is CVE-2026-120756 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-120756 being exploited in the wild.
- How severe is CVE-2026-120756?
- Informational severity, published 3 November 2026.
- Which products and versions are affected?
- Hdfgroup Hdf5 through 2.2.0.
- Is there a fix for CVE-2026-120756?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-120756 attacked?
- It is attacked with local access, in a software library.
- Am I affected by CVE-2026-120756?
- Check whether you run Hdfgroup Hdf5 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
The vulnerability is a heap buffer over-read in H5O__chunk_deserialize() in src/H5Ocache.c. When decoding object header messages, the declared message size is checked against the chunk boundary before the full message header (including flags and optional creation index fields) is decoded. Since the message body starts after these header fields, a crafted file can declare a size that passes the initial check but extends beyond the chunk, causing decode callbacks to read past the allocated buffer. The flaw is triggered during H5Fopen() on a malicious file without requiring prior authentication or special privileges.
Affected products
- HDFGroup HDF5 through 2.2.0
Timeline
- 2026-11-03: disclosed