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Critical, CVSS 9.8amended

H2O affected by a deserialization vulnerability

CVE-2025-6544GHSA-5w3j-gwgh-4rfv

What to do

Vendor response not established. Follow the primary source's mitigation guidance and check back for a fix.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI h2o

    Affected
    <= 3.46.0.7
    Fixed in
    no fixed version recorded

  • Maven ai.h2o:h2o-core

    Affected
    <= 3.46.0.7
    Fixed in
    no fixed version recorded

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
9.8 · CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS
  • CVE-2025-6544: 0.95% estimated exploitation activity in the next 30 days; percentile 61.36 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

A deserialization vulnerability exists in h2oai/h2o-3 versions <= 3.46.0.7, allowing attackers to read arbitrary system files and execute arbitrary code. The vulnerability arises from improper handling of JDBC connection parameters, which can be exploited by bypassing regular expression checks and using double URL encoding. This issue impacts all users of the affected versions.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 4 · amended ·

    Amended from osv record GHSA-5w3j-gwgh-4rfv

  2. Revision 3 · amended ·

    Amended from ghsa record GHSA-5w3j-gwgh-4rfv

  3. Revision 2 · amended ·

    Amended from ghsa record GHSA-5w3j-gwgh-4rfv

  4. Revision 1 · created ·

    Published from osv record GHSA-5w3j-gwgh-4rfv

Agent brief

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# Patch Next advisory brief: CVE-2025-6544

Advisory: H2O affected by a deserialization vulnerability
IDs: CVE-2025-6544, GHSA-5w3j-gwgh-4rfv
Record: https://patchnext.com/advisories/cve-2025-6544 (revision 4, source checked 28 Oct 2026, 06:05 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI h2o: affected <= 3.46.0.7
- Maven ai.h2o:h2o-core: affected <= 3.46.0.7

## Suggested inspection (read-only)
- `python -m pip show h2o`: prints the installed version. Run with the environment that serves production active.
- Maven ai.h2o:h2o-core: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on h2o, ai.h2o:h2o-core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-5w3j-gwgh-4rfv (OSV record GHSA-5w3j-gwgh-4rfv lists affected ranges: Maven ai.h2o:h2o-core >=0 =0 <=3.46.0.7)
- Verified: https://github.com/advisories/GHSA-5w3j-gwgh-4rfv (GitHub-reviewed advisory GHSA-5w3j-gwgh-4rfv lists affected ranges: Maven ai.h2o:h2o-core >=0 =0 <=3.46.0.7)

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