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Vulnerability record · CVE-2025-6544 · published 21 September 2025

CVE-2025-6544: H2o deserialization of untrusted data vulnerability

H2o · H2o

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.

9.8 CVSS 3.0 Critical EPSS 0.92% · top 41.3% CWE-502 · Deserialization of untrusted data
9.8CVSS 3.0 base score
0.92%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
3References, 2 tagged exploit
17 Jun 2026Last modified by NVD

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.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/h2oai/h2o-3/commit/0298ee348f5c73673b7b542158081e79605f5f25 Patch
https://huntr.com/bounties/53f35a0f-d644-4f82-93aa-89fe7e0aed40 ExploitThird Party Advisory
https://huntr.com/bounties/53f35a0f-d644-4f82-93aa-89fe7e0aed40 ExploitThird Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2026-3960H2o code injection vulnerabilityA critical remote code execution vulnerability exists in the unauthenticated REST API endpoint /99/ImportSQLTable in H2O-3 version 3.46.0.9 and prior…EPSS 1.0%9.8CVE-2024-10553H2o deserialization of untrusted data vulnerabilityA vulnerability in the h2oai/h2o-3 REST API versions 3.46.0.4 allows unauthenticated remote attackers to execute arbitrary code via deserialization o…EPSS 1.6%9.8CVE-2023-6016H2o code injection vulnerabilityAn attacker is able to gain remote code execution on a server hosting the H2O dashboard through it's POJO model import feature.EPSS 31%9.1CVE-2024-45758H2o deserialization of untrusted data vulnerabilityH2O.ai H2O through 3.46.0.4 allows attackers to arbitrarily set the JDBC URL, leading to deserialization attacks, file reads, and command execution. …EPSS 0.91%8.2CVE-2024-8616H2o vulnerabilityIn h2oai/h2o-3 version 3.46.0, the `/99/Models/{name}/json` endpoint allows for arbitrary file overwrite on the target server. The vulnerability aris…EPSS 0.55%8.2CVE-2023-6569H2o vulnerabilityExternal Control of File Name or Path in h2oai/h2o-3EPSS 0.72%7.5CVE-2026-54340H2o uncontrolled resource consumption vulnerabilityh2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 9265bdd, there is an HTTP/2 state amplification issue that combin…EPSS 0.49%7.5CVE-2026-44453H2o allocation without limits vulnerabilityh2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 6b5370d, h2o is vulnerable to a Denial of Service attack when cal…EPSS 0.49%

Source: NIST National Vulnerability Database (record CVE-2025-6544), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.