What is the CVSS score of CVE-2025-6544?

CVE-2025-6544 has a CVSS 3.0 base score of 9.8 (Critical). CVSS vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 0.4%.

Which versions of H2O are affected by CVE-2025-6544?

Organizations using h2oai/h2o-3 face critical risk from CVE-2025-6544, a insecure deserialization vulnerability rated CVSS 9.8.. A patch is available.

Is there a public PoC exploit available for CVE-2025-6544?

Yes, a public proof-of-concept exploit is available for CVE-2025-6544. Prioritise patching immediately. EPSS: 0.4%.

How to fix or mitigate CVE-2025-6544?

Within 24 hours: Identify all affected systems running h2oai/h2o-3 and apply vendor patches immediately. Restrict deserialization to trusted data sources and implement integrity checks.

H2O CVE-2025-6544

CRITICAL

Deserialization of Untrusted Data (CWE-502)

2025-09-21 security@huntr.dev

RCE Deserialization H2O

9.8

CVSS 3.0 · NVD

Severity by source

NVD PRIMARY

9.8 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Analysis Generated

Mar 28, 2026 - 19:13 vuln.today

Patch released

Mar 28, 2026 - 19:13 nvd

Patch available

PoC Detected

Oct 08, 2025 - 20:05 vuln.today

Public exploit code

CVE Published

Sep 21, 2025 - 09:15 nvd

CRITICAL 9.8

Blast Radius

ecosystem impact

† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth

20 maven packages depend on ai.h2o:h2o-core (20 direct, 0 indirect)
3 pypi packages depend on h2o (3 direct, 0 indirect)

Ecosystem-wide dependent count for version 3.46.0.7 and other introduced versions.

DescriptionCVE.org

A deserialization vulnerability exists in h2oai/h2o-3 versions <= 3.46.0.8, 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.

AnalysisAI

A deserialization vulnerability exists in h2oai/h2o-3 versions <= 3.46.0.8, allowing attackers to read arbitrary system files and execute arbitrary code. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.

Technical ContextAI

This vulnerability is classified as Deserialization of Untrusted Data (CWE-502), which allows attackers to execute arbitrary code through malicious serialized objects. A deserialization vulnerability exists in h2oai/h2o-3 versions <= 3.46.0.8, 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. Affected products include: H2O.

RemediationAI

A vendor patch is available. Apply the latest security update as soon as possible. Avoid deserializing untrusted data. Use safe serialization formats (JSON). Implement integrity checks and type allowlists.