# CVE-2026-120757: Heap Buffer Over-read via Non-Terminated Link Data in H5L__extern_traverse

Status: published. Published: 2026-11-03. Updated: 2026-11-03.

HDF5 through 2.2.0 contains a heap buffer over-read vulnerability in H5L__extern_traverse() in src/H5Lexternal.c, the default traversal callback for external links. The callback locates the target file name and object path within the link’s user data using strlen() without validating the buffer against its stored size (udata_size, which was marked unused). A crafted HDF5 file containing an external link whose data is not NULL-terminated, or is too short to hold both strings, causes strlen() to read past the end of the udata heap buffer, and the derived object path pointer may also point outside the buffer. The overrun is unbounded and continues until a zero byte is found. The flaw is triggered when the malicious link is traversed, for example when opening an object through it. An attacker who can get a user or application to access a crafted file can cause a denial of service, and adjacent heap contents may be incorporated into the external file name or object path the library attempts to open.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- The HDF Group / HDF5: < 2.3.0 (affected). Source: CNA: HDFG

## Severity and prioritization

- CVSS 4.0: 6.9 (medium); CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N; source: CNA: HDFG

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-125

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/HDFGroup/hdf5/pull/6708 (CNA: HDFG)

## Provenance

- CNA: HDFG: https://www.cve.org/CVERecord?id=CVE-2026-120757; retrieved 2026-11-03; source updated 2026-11-03

Revision: 8259f25b06f1eea1c37220444de9b20347b679cf78bf96dd7fed9f3eac93d91a

Canonical: https://y2.dev/cve/CVE-2026-120757

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