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

Source: https://junglewise.ai/threats/cve-2025-6544-h2o-affected-by-a-deserialization-vulnerability  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-09-22  
License: CC BY 4.0 with a link back

CVE-2025-6544 · Severity: critical · CVSS 9.8 · Published 2025-09-22

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.

Technologies: [ai.h2o:h2o-core (Maven)](https://junglewise.ai/threats/technologies/ai-h2o-h2o-core), [h2o (PyPI)](https://junglewise.ai/threats/technologies/h2o). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven), [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2025-6544 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-6544 being exploited in the wild.

**How severe is CVE-2025-6544?** Critical severity, with a CVSS score of 9.8, published 22 September 2025.

**Which products and versions are affected?** ai.h2o:h2o-core (Maven) <= 3.46.0.7, ECOSYSTEM:introduced=0,last_affected=3.46.0.7; h2o (PyPI) <= 3.46.0.7, ECOSYSTEM:introduced=0,last_affected=3.46.0.7.

**Is there a fix for CVE-2025-6544?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**Am I affected by CVE-2025-6544?** Check whether you run ai.h2o:h2o-core (Maven) or h2o (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Affected products

- ai.h2o:h2o-core (Maven) <= 3.46.0.7, ECOSYSTEM:introduced=0,last_affected=3.46.0.7
- h2o (PyPI) <= 3.46.0.7, ECOSYSTEM:introduced=0,last_affected=3.46.0.7

## Identifiers

- CVE-2025-6544
- GHSA-5w3j-gwgh-4rfv
- PYSEC-2026-349

## Related threats

- [PYSEC-2026-1441 - H2O Vulnerable to Arbitrary File Overwrite](https://junglewise.ai/threats/cve-2024-8616-h2o-vulnerable-to-arbitrary-file-overwrite)
- [PYSEC-2026-1438 - H2O Vulnerable to Denial of Service (DoS) via `HEAD` Request](https://junglewise.ai/threats/cve-2024-8062-h2o-vulnerable-to-denial-of-service-dos-via-head-request)
- [PYSEC-2026-1443 - H2O Vulnerable to Denial of Service (DoS) via `/3/ImportFiles` Endpoint](https://junglewise.ai/threats/cve-2024-7768-h2o-vulnerable-to-denial-of-service-dos-via-3-importfiles-endpoint)
- [PYSEC-2026-1439 - H2O Vulnerable to Denial of Service (DoS) via Large GZIP Parsing](https://junglewise.ai/threats/cve-2024-7765-h2o-vulnerable-to-denial-of-service-dos-via-large-gzip-parsing)
- [PYSEC-2026-1442 - H2O Vulnerable to Execution of Arbitrary Files](https://junglewise.ai/threats/cve-2024-6863-h2o-vulnerable-to-execution-of-arbitrary-files)