CVE-2025-6544 Deserialization Vulnerability in h2oai/h2o-3
Attackers can execute arbitrary code and read system files via deserialization flaws in H2O-3 JDBC connection parameters.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2025-6544?
CVE-2025-6544 is a critical unsafe deserialization vulnerability in h2oai/h2o-3, published on 21 Sep 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-502
Which versions are affected by CVE-2025-6544?
5 open source packages ship an affected version, including h2o and ai.h2o:h2o-core. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
h2o PyPI | All versions to 3.46.0.7 | None |
h2o PyPI | All versions to 3.46.0.7 | None |
h2o PyPI | All versions to 3.46.0.7 | None |
ai.h2o:h2o-core Maven | All versions to 3.46.0.7 | None |
ai.h2o:h2o-core Maven | All versions to 3.46.0.7 | None |
Products include H2o H2o.
How do I fix CVE-2025-6544?
No fix has been published for CVE-2025-6544 yet. Limit exposure of the affected software until one is available.
Upgrade, and only deserialise data from trusted sources or with an allow-list of types. More about Unsafe deserialization.
Is CVE-2025-6544 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-6544 exists.
Other vulnerabilities in h2oai/h2o-3
Sources
Also known as GHSA-5w3j-gwgh-4rfv, PYSEC-2026-349.