CVE-2025-6544: H2o core H2O Affected By A Deserialization Vulnerability

CRITICAL
Advisory Identifier: GHSA-5w3j-gwgh-4rfv
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CVSS 9.8
CWE-502
Published
Advisory Summary

CVE-2025-6544 is a CRITICAL (CVSS 9.8) h2o affected by a deserialization vulnerability (CWE-502: Deserialization of Untrusted Data) affecting H2o core libraries in the Maven ecosystem. The issue involves h2o affected by a deserialization vulnerability. Remediation is available in the latest vendor maintenance releases.

CVE-2025-6544 at a Glance

CVE Identifier CVE-2025-6544
GHSA Identifier GHSA-5w3j-gwgh-4rfv
Severity CRITICAL
CVSS v3.1 Base Score 9.8
CWE Classification CWE-502: Deserialization of Untrusted Data
Affected Product H2o core
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 9.8

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2025-6544

To remediate this vulnerability, upgrade all affected H2o core dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

ai.h2o:h2o-core fixed: Latest secure release 
<dependency>
    <groupId>ai.h2o</groupId>
    <artifactId>h2o-core</artifactId>
    <version>Latest secure release</version>
</dependency>
h2o fixed: Latest secure release 
pip install h2o>=Latest secure release
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree -Dincludes=ai.h2o

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2025-6544, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree -Dincludes=ai.h2o

Analyze the terminal output to locate any version of H2o core in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The mvn dependency:tree -Dincludes=ai.h2o command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-502: Deserialization of Untrusted Data, where the product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid. In H2o core, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

CVE-2025-6544 Affected H2o core Versions

2 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
ai.h2o:h2o-core
maven/ai.h2o/h2o-core
Maven
≤ 3.46.0.7
h2o
pypi/h2o
PyPI
≤ 3.46.0.7

References

NVD — CVE-2025-6544 NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-6544
Security Fix Commit FIX COMMIT
https://github.com/h2oai/h2o-3/commit/0298ee348f5c73673b7b542158081e79605f5f25
H2o core Source Repository REPOSITORY
https://github.com/h2oai/h2o-3
huntr.com/bounties/53f35a0f-d... WEB
https://huntr.com/bounties/53f35a0f-d644-4f82-93aa-89fe7e0aed40

Frequently Asked Questions

What is CVE-2025-6544?
CVE-2025-6544 is a security vulnerability in H2o core involving H2O affected by a deserialization vulnerability under CWE-502: Deserialization of Untrusted Data.
Which H2o core versions are affected?
Affected versions include releases prior to current release patches across affected packages: ai.h2o:h2o-core, h2o.
What version fixes CVE-2025-6544?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is h2o-core affected?
Yes, ai.h2o:h2o-core is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
Is h2o affected?
Yes, h2o is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
What is the CVSS score of CVE-2025-6544?
CVE-2025-6544 has a CVSS v3.1 base score of 9.8 (CRITICAL) with vector string CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2025-6544?
CVE-2025-6544 is classified under CWE-502: Deserialization of Untrusted Data (The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.).
How can I check Maven dependencies for CVE-2025-6544?
Run the dependency tree command: 'mvn dependency:tree -Dincludes=ai.h2o'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5w3j-gwgh-4rfv",
  "modified" : "2025-09-22T21:09:54Z",
  "published" : "2025-09-22T18:30:34Z",
  "aliases" : [ "CVE-2025-6544" ],
  "summary" : "H2O affected by a deserialization vulnerability",
  "details" : "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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "ai.h2o:h2o-core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "3.46.0.7"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "h2o"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "3.46.0.7"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-6544"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/h2oai/h2o-3/commit/0298ee348f5c73673b7b542158081e79605f5f25"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/h2oai/h2o-3"
  }, {
    "type" : "WEB",
    "url" : "https://huntr.com/bounties/53f35a0f-d644-4f82-93aa-89fe7e0aed40"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-502" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-09-22T21:09:54Z",
    "nvd_published_at" : "2025-09-21T09:15:38Z"
  }
}