---
title: "CVE-2025-6544: H2O affected by a deserialization vulnerability"
url: https://erroneo.us/security/cve/CVE-2025-6544/
description: "CVE-2025-6544 (ai.h2o:h2o-core (Maven)): A deserialization vulnerability exists in h2oai/h2o-3 versions"
type: vulnerability-record
section: "Security Digest"
date_published: 2025-09-21
date_modified: 2025-09-22
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2025-6544"
kev: false
cvss: 9.8
epss: 0.00919
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2025-6544: H2O affected by a deserialization vulnerability

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.9% , percentile 60: FIRST’s model estimates a 0.9% chance of exploitation activity in the next 30 days, higher than 60% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes ai.h2o:h2o-core (Maven) <= 3.46.0.7, no fixed version listed ; h2o (PyPI) <= 3.46.0.7, no fixed version listed . Check your lockfile, including transitive dependencies.

## What it is

A deserialization vulnerability exists in h2oai/h2o-3 versions

## Affected packages

- Maven `ai.h2o:h2o-core` <= 3.46.0.7 → fixed: none listed
- PyPI `h2o` <= 3.46.0.7 → fixed: none listed

## Affected products (CVE record)

- h2oai h2oai/h2o-3: unspecified < 3.46.8

## Severity

- @huntr_ai CVSS 3.0: 9.8 `CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
- GitHub CVSS 3.1: 9.8 `CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.92% probability of exploitation activity in the next 30 days; percentile 60.

## Sources

- [GitHub Advisory GHSA-5w3j-gwgh-4rfv](https://github.com/advisories/GHSA-5w3j-gwgh-4rfv)
- [CVE.org record CVE-2025-6544](https://www.cve.org/CVERecord?id=CVE-2025-6544)
- [NVD entry CVE-2025-6544](https://nvd.nist.gov/vuln/detail/CVE-2025-6544)
- [huntr.com](https://huntr.com/bounties/53f35a0f-d644-4f82-93aa-89fe7e0aed40)
- [github.com](https://github.com/h2oai/h2o-3/commit/0298ee348f5c73673b7b542158081e79605f5f25)

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Source page: https://erroneo.us/security/cve/CVE-2025-6544/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt