Overview
Recently, NSFOCUS CERT detected that H2O-3 released a security update to fix the H2O-3 JDBC deserialization vulnerability (CVE-2025-6544); This vulnerability is a bypass of CVE-2025-6507. Due to the system’s flawed handling of JDBC connection parameters, an unauthenticated attacker can bypass existing regular expression checks through double URL encoding, thereby enabling arbitrary file reading and remote code execution. The CVSS score is 9.8. At present, the vulnerability details and PoC have been made public. Relevant users are requested to take measures to protect themselves as soon as possible.
H2O-3 is an open source, distributed, scalable machine learning platform for quickly building and deploying machine learning models on big data.
Reference link: https://www.cve.org/CVERecord? id=CVE-2025-6544
Scope of Impact
Affected versions
- H2O-3 <= 3.46.0.8
Unaffected version
- H2O-3 > 3.46.0.8
Risk Investigation of Exposure Surface
Cloud detection
NSFOCUS’s External Attack Surface Management Service (EASM) supports Internet asset investigation of CVE-2025-6544 vulnerability risks. It has helped service customer groups complete exposure surface investigations and conduct vulnerability warnings and closed-loop disposal in a timely manner before threats occur. Interested customers can arrange detailed consultation and communication by contacting their local regional colleagues at NSFOCUS or sending an email to rs@nsfocus.com.
Mitigation
Official upgrade
At present, the official has released a new version to fix this vulnerability. Affected users are requested to upgrade their protection as soon as possible.
Download link: https://github.com/h2oai/h2o-3/tags
Temporary protective measures
If the relevant users are temporarily unable to perform upgrade operations, access restrictions can be imposed on the H2O-3 port (default 54321) without affecting business.
Statement
This advisory is only used to describe a potential risk. NSFOCUS does not provide any commitment or promise on this advisory. NSFOCUS and the author will not bear any liability for any direct and/or indirect consequences and losses caused by transmitting and/or using this advisory. NSFOCUS reserves all the rights to modify and interpret this advisory. Please include this statement paragraph when reproducing or transferring this advisory. Do not modify this advisory, add/delete any information to/from it, or use this advisory for commercial purposes without permission from NSFOCUS.
About NSFOCUS
NSFOCUS, a pioneering leader in cybersecurity, is dedicated to safeguarding telecommunications, Internet service providers, hosting providers, and enterprises from sophisticated cyberattacks.
Founded in 2000, NSFOCUS operates globally with over 4000 employees at two headquarters in Beijing, China, and Santa Clara, CA, USA, and over 50 offices worldwide. It has a proven track record of protecting over 25% of the Fortune Global 500 companies, including four of the five largest banks and six of the world’s top ten telecommunications companies.
Leveraging technical prowess and innovation, NSFOCUS delivers a comprehensive suite of security solutions, including the Intelligent Security Operations Platform (ISOP) for modern SOC, DDoS Protection, Continuous Threat Exposure Management (CTEM) Service and Web Application and API Protection (WAAP). All the solutions and services are augmented by the Security Large Language Model (SecLLM), ML, patented algorithms and other cutting-edge research achievements developed by NSFOCUS.
