CVE-2025-6544 is a critical-severity (CVSS 9.8) Deserialization of Untrusted Data vulnerability in ai.h2o:h2o-core. The records list no fixed version yet; check the vendor advisory below and apply the mitigations in the meantime.
Deserialization Vulnerability in h2oai/h2o-3
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-6544.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
ai.h2o:h2o-core🐍h2oReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven, PyPI packages — download data is not available via public APIs for these ecosystems.
Description
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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | ai.h2o:h2o-core | all versions | No fix |
| 🐍PyPI | h2o | all versions | No fix |
Affected Products
h2oh2oDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ai.h2o:h2o-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Remediation status
The records we use list no patched version of ai.h2o:h2o-core for CVE-2025-6544. Check the maintainer's advisory, and where your build allows, override or pin the dependency away from the vulnerable range.
Mitigate without a patch
Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.
Frequently Asked Questions
Is CVE-2025-6544 in your dependencies?
Find it across Maven, PyPI, including transitive dependencies.