CVE-2025-6507: H2O-3 Deserialization RCE Vulnerability

CVE-2025-6507 Overview

A critical insecure deserialization vulnerability has been identified in the h2oai/h2o-3 machine learning platform that allows attackers to exploit deserialization of untrusted data through JDBC connection parameter manipulation. This vulnerability enables arbitrary code execution and unauthorized reading of system files on affected systems. The issue affects the master branch version 3.47.0.99999 and arises from inadequate regular expression filters intended to prevent malicious parameter injection in JDBC connections.

Critical Impact

Attackers can achieve remote code execution and read sensitive system files by bypassing regex-based parameter filters through whitespace manipulation in JDBC connection strings.

Affected Products

• H2O-3 version 3.47.0.99999 (master branch)
• H2O-3 versions prior to 3.46.0.8

Discovery Timeline

• 2025-09-01 - CVE-2025-6507 published to NVD
• 2025-09-02 - Last updated in NVD database

Technical Details for CVE-2025-6507

Vulnerability Analysis

This vulnerability represents a classic case of insufficient input validation combined with insecure deserialization (CWE-502). The H2O-3 platform implements security controls to prevent malicious JDBC connection parameters that could enable dangerous features like autoDeserialize in MySQL connectors. However, the regex pattern used to detect these parameters can be bypassed by inserting whitespace characters between parameter names and their values.

When attackers successfully inject malicious parameters, they can leverage database connector features designed for legitimate serialization purposes to execute arbitrary code on the target system. This is particularly dangerous in data science and machine learning environments where H2O-3 is deployed, as these systems often have elevated privileges and access to sensitive data.

Root Cause

The root cause lies in the overly permissive regex pattern used in the SQLManager.java class to detect and block dangerous JDBC parameters. The original pattern -(?i)[?;&]([a-z]+)= only matched parameters immediately preceded by connection string delimiters (?, ;, or &) and required the parameter name to be directly adjacent to the equals sign. This design flaw allowed attackers to evade detection by inserting spaces between parameter names and their values, effectively bypassing the security filter.

Attack Vector

The attack exploits the network-accessible JDBC connection functionality in H2O-3. Attackers craft malicious JDBC connection strings with carefully placed whitespace to bypass parameter validation. For example, inserting spaces like autoDeserialize = true instead of autoDeserialize=true would evade the original regex filter. Once the malicious parameter is accepted, the attacker can leverage MySQL's deserialization features to achieve code execution or file read operations.

// Security patch in SQLManager.java
// Source: https://github.com/h2oai/h2o-3/commit/f714edd6b8429c7a7211b779b6ec108a95b7382d

  private static final String DISALLOWED_JDBC_PARAMETERS_PARAM = H2O.OptArgs.SYSTEM_PROP_PREFIX + "sql.jdbc.disallowed.parameters";

-  private static final Pattern JDBC_PARAMETERS_REGEX_PATTERN = Pattern.compile("(?i)[?;&]([a-z]+)=");
+  private static final Pattern JDBC_PARAMETERS_REGEX_PATTERN = Pattern.compile("(?i)([a-z0-9_]+)\\s*=\\s*");

  private static final List<String> DEFAULT_JDBC_DISALLOWED_PARAMETERS = Stream.of(
          "autoDeserialize", "queryInterceptors", "allowLoadLocalInfile", "allowMultiQueries", //mysql

The patch addresses this by updating the regex pattern to use \\s* which matches zero or more whitespace characters around the equals sign, ensuring parameters cannot bypass detection through whitespace manipulation. The pattern also now matches parameter names containing digits and underscores.

Detection Methods for CVE-2025-6507

Indicators of Compromise

• Unusual JDBC connection strings containing whitespace around parameter assignments in application logs
• Unexpected MySQL connector parameters such as autoDeserialize, queryInterceptors, or allowLoadLocalInfile in database connection attempts
• Evidence of file read operations or code execution originating from H2O-3 processes
• Anomalous network connections from H2O-3 instances to external database servers

Detection Strategies

• Monitor H2O-3 application logs for JDBC connection strings containing suspicious parameters with irregular whitespace patterns
• Implement network monitoring to detect unusual database connection patterns from H2O-3 instances
• Deploy endpoint detection to identify unexpected child processes spawned by H2O-3 Java processes
• Use application-layer firewalls to inspect and block malformed JDBC connection strings

Monitoring Recommendations

• Enable detailed logging for all JDBC connection attempts in H2O-3 deployments
• Configure alerts for file access operations from H2O-3 processes outside normal working directories
• Monitor for deserialization-related Java exceptions in application error logs
• Implement network segmentation monitoring to detect lateral movement from compromised H2O-3 instances

How to Mitigate CVE-2025-6507

Immediate Actions Required

• Upgrade H2O-3 to version 3.46.0.8 or later immediately
• Audit existing JDBC connection configurations for potentially malicious parameters
• Restrict network access to H2O-3 instances to trusted sources only
• Review system logs for signs of exploitation prior to patching

Patch Information

The vulnerability has been addressed in H2O-3 version 3.46.0.8. The fix implements a more robust regex pattern that properly handles whitespace around parameter assignments, preventing the bypass technique. The security patch is available through the GitHub commit f714edd6b8429c7a7211b779b6ec108a95b7382d. Additional details about this vulnerability and the associated bounty can be found at the Huntr vulnerability disclosure.

Workarounds

• If immediate patching is not possible, restrict JDBC connectivity by blocking access to external databases
• Implement a web application firewall or reverse proxy to filter JDBC connection strings before they reach H2O-3
• Disable unnecessary database connectivity features in H2O-3 configuration
• Deploy network segmentation to isolate H2O-3 instances from sensitive systems

# Configuration example - Restrict JDBC connectivity at the network level
# Block outbound MySQL connections from H2O-3 servers
iptables -A OUTPUT -p tcp --dport 3306 -m owner --uid-owner h2o -j DROP

# Allow only trusted database servers
iptables -A OUTPUT -p tcp --dport 3306 -d trusted_db_server_ip -m owner --uid-owner h2o -j ACCEPT