Deserialization in H2o
CVE-2025-6544
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.
Vulnerability class: Insecure Deserialization
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.009 (58.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 59th percentile — 58.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000
Affected products
- H2o
- H2oai H2oai/h2o-3 — versions unspecified
Weakness classification (CWE)
Public proof-of-concept exploits
References
- huntr.com/bounties/53f35a0f-d644-4f82-93aa-89fe7e0aed40 (Exploit, Third Party Advisory)
- github.com/h2oai/h2o-3/commit/0298ee348f5c73673b7b542158081e79605f5f25 (Patch)
Frequently asked questions
- What is CVE-2025-6544?
- CVE-2025-6544 is a critical-severity vulnerability in H2o, classified under Deserialization of Untrusted Data. CVSS score: 9.8/10. Published 2025-09-21.
- How severe is CVE-2025-6544?
- Critical severity. CVSS v3 base score is 9.8 out of 10.
- Is CVE-2025-6544 known to be exploited?
- 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.