# CVE-2026-19027: HDF5 out-of-bounds heap read in N-Bit filter decompression

> Attackers can disclose adjacent heap memory via crafted HDF5 files due to an out-of-bounds read in the N-Bit filter decompression logic.

- **Severity:** Medium 6.9 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 5 Aug 2026
- **Updated:** 6 Oct 2026
- **Also known as:** AZL-94496, DEBIAN-CVE-2026-19027, ECHO-c165-82fe-ea22, GHSA-2pvh-qgr3-wp2r, UBUNTU-CVE-2026-19027

## What is CVE-2026-19027?

CVE-2026-19027 is a medium-severity vulnerability in The HDF Group HDF5, published on 5 Aug 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

The H5Z__nbit_decompress_one_byte, H5Z__nbit_decompress_one_nooptype, and H5Z__nbit_decompress_one_atomic functions in H5Znbit.c in HDF5
prior to 2.3.0 advance a read index into the compressed chunk buffer without bounding it against the buffer's actual size. This allows attackers to cause an out-of-bounds heap read, and in constrained cases disclosure of adjacent heap memory into decompressed dataset values, via a crafted HDF5 file whose N-Bit filter parameters describe more decompressed data than the stored compressed chunk actually contains, triggered via H5Dread, e.g. by the h5ls or h5repack tools.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-19027?


## How do I fix CVE-2026-19027?

Upgrade to a fixed version.

## Is CVE-2026-19027 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-19027 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-19027 and fix it if it is affected.

What it is: CVE-2026-19027 is a medium-severity vulnerability in The HDF Group HDF5, published on 5 Aug 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-19027 exists.

Affected product: The HDF Group HDF5. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-19027/ (Markdown: https://insights.sbomify.com/CVE-2026-19027/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-19027
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-19027
- OSV: https://osv.dev/vulnerability/CVE-2026-19027

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-19027/
Summaries are generated and may contain mistakes; the official description above is the record.