HDF5: Out-of-bounds Read
CVE-2026-120757 is a high-severity out-of-bounds read vulnerability in HDF5 from The HDF Group, with a CVSS 3.1 base score of 7.1 out of 10. It can be exploited with local access to the system by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. Affected HDF5 versions: < 2.3.0. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.15% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of HDF5 you run against the affected versions below, and install the vendor's latest release.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| The HDF Group | HDF5 | < 2.3.0 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 6.9 | Medium | CNA |
| CVSS 3.1 | 7.1 | High | NVD |
Official description
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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Out-of-bounds Read
The product reads data past the end, or before the beginning, of the intended buffer.
How developers prevent this class of flaw
- Use a language that provides appropriate memory abstractions.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
References
Patches and release notes
- github.com/HDFGroup/hdf5/pull/6708Issue Tracking
Other vulnerabilities in HDF5
- 8.5 High severity
- 8.2 High severity
Recent Out-of-bounds Read vulnerabilities
- 8.8 High severity
- 7.4 High severity
- 8.8 High severity
- 7.4 High severity
- 8.3 High severity
- 8.3 High severity
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