# CVE-2026-120757: HDF5 heap buffer over-read in external link traversal

Source: https://junglewise.ai/threats/cve-2026-120757-hdf5-through-2-2-0-contains-a-heap-buffer-over-read  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-03. Updated: 2026-11-03  
License: CC BY 4.0 with a link back

CVE-2026-120757 · Severity: info · Published 2026-11-03

HDF5 is a data management library used to store and organize large amounts of scientific and research data. When opening a crafted HDF5 file containing a malformed external link, the library can read beyond the bounds of a memory buffer, potentially exposing adjacent data in memory or causing the application to crash. An attacker can exploit this by providing a malicious file that triggers a denial of service.

Technologies: [HDF Group HDF5](https://junglewise.ai/threats/technologies/hdf-group-hdf5). Vendors: [HDF Group](https://junglewise.ai/threats/vendors/hdf-group).

## Quick answers

**Is CVE-2026-120757 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-120757 being exploited in the wild.

**How severe is CVE-2026-120757?** Informational severity, published 3 November 2026.

**Which products and versions are affected?** HDF Group HDF5 through 2.2.0.

**Is there a fix for CVE-2026-120757?** A patch was published on 2026-10-08. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-120757 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-120757?** Check whether you run HDF Group 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

A heap buffer over-read in H5L__extern_traverse() fails to validate the size of external link user data before parsing strings within it using strlen(). The vulnerable code ignores the udata_size parameter and continues reading until a null byte is found, allowing reads past the allocated buffer boundary. The vulnerability is triggered when a malicious external link is traversed during file object access, potentially incorporating adjacent heap memory into filenames or object paths the library attempts to open.

## Affected products

- HDF Group HDF5 through 2.2.0

## Timeline

- 2026-11-03: disclosed
- 2026-10-08: patched

## References

- [https://github.com/HDFGroup/hdf5/pull/6708](https://github.com/HDFGroup/hdf5/pull/6708)

## Related threats

- [HDF5 uninitialized memory read in scaleoffset filter](https://junglewise.ai/threats/cve-2026-120754-hdf5-through-2-2-0-contains-an-uninitialized-memory-read)
- [HDF5 heap buffer over-read in scale-offset filter decode](https://junglewise.ai/threats/cve-2026-19029-a-heap-based-buffer-over-read-in-h5z-filter-scaleoffset-in-src)
- [HDF5 heap-based buffer overflow in H5VM_array_fill](https://junglewise.ai/threats/cve-2026-106547-a-heap-based-buffer-overflow-in-h5vm-array-fill-in-src-h5vm-c-in)