# CVE-2026-19028: HDF5 integer underflow in Fletcher32 filter leads to massive out-of-bounds read

> Attackers can cause denial of service via crafted HDF5 files triggering an integer underflow and out-of-bounds read in the Fletcher32 filter.

- **Severity:** Medium 6.8 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/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-94499, DEBIAN-CVE-2026-19028, ECHO-a9d3-2518-671d, GHSA-2hg9-348w-39gj, UBUNTU-CVE-2026-19028

## What is CVE-2026-19028?

CVE-2026-19028 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

H5Z__filter_fletcher32 in H5Zfletcher32.c in HDF5 prior to 2.3.0 computes the data length to checksum by subtracting the 4-byte trailing checksum size from the input buffer size without checking that the buffer is at least 4 bytes, allowing a size_t underflow. This allows attackers to cause a denial of service (massively out-of-bounds read and application crash in H5_checksum_fletcher32) via a crafted HDF5 file with a Fletcher32-filtered chunk smaller than 4 bytes, triggered via H5Dread, e.g. by the h5ls or h5dump tools.

Weakness: CWE-190 (Integer Overflow or Wraparound), CWE-1284 (Improper Validation of Specified Quantity in Input), CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-19028?


## How do I fix CVE-2026-19028?

Upgrade to a fixed version.

## Is CVE-2026-19028 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-19028 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-19028 and fix it if it is affected.

What it is: CVE-2026-19028 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-2026-19028 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-2026-19028/ (Markdown: https://insights.sbomify.com/CVE-2026-19028/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-19028
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-19028
- OSV: https://osv.dev/vulnerability/CVE-2026-19028

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-19028/
Summaries are generated and may contain mistakes; the official description above is the record.