CVE-2024-5986: H2O.ai H2O-3 RCE Vulnerability

CVE-2024-5986 Overview

A critical arbitrary file write vulnerability exists in h2oai/h2o-3 version 3.46.0.1 that allows remote attackers to write arbitrary data to any file on the server. This vulnerability is exploited by chaining the /3/Parse endpoint with the /3/Frames/framename/export endpoint, enabling attackers to inject malicious content as headers into files and export them to arbitrary locations on the filesystem.

Critical Impact

Remote attackers can overwrite critical system files including private SSH keys, crontab entries, or script files, potentially leading to remote code execution and complete system compromise.

Affected Products

• h2oai/h2o-3 version 3.46.0.1

Discovery Timeline

• 2026-02-02 - CVE CVE-2024-5986 published to NVD
• 2026-02-03 - Last updated in NVD database

Technical Details for CVE-2024-5986

Vulnerability Analysis

This vulnerability is classified under CWE-73 (External Control of File Name or Path), representing a severe arbitrary file write condition. The flaw allows unauthenticated remote attackers to write attacker-controlled content to any file path accessible to the H2O-3 process on the target server.

The attack chain leverages two legitimate API endpoints in combination. The /3/Parse endpoint is designed to parse data files and create frames from them, while the /3/Frames/framename/export endpoint exports frame data to files. By manipulating the parsing process, attackers can inject arbitrary data as the header of an empty file, then use the export functionality to write this malicious content to any location on the filesystem.

The impact is severe as it enables attackers to overwrite security-critical files such as ~/.ssh/authorized_keys to add rogue SSH keys, modify crontab files to schedule malicious commands, or replace legitimate script files with malicious versions that execute when triggered.

Root Cause

The root cause lies in insufficient validation and sanitization of user-controlled input in the file parsing and export pipeline. The application fails to properly restrict the file path destinations for exported frames and does not adequately validate the content being written. This external control of file names and paths allows attackers to escape intended directory boundaries and write to arbitrary filesystem locations.

Attack Vector

The attack is network-accessible and requires no authentication or user interaction. An attacker can remotely exploit this vulnerability by:

1. Sending a crafted request to the /3/Parse endpoint with malicious header content
2. Creating an empty data frame with the injected content as header information
3. Using the /3/Frames/framename/export endpoint to export the frame to an arbitrary file path
4. The malicious content is written to the target file, overwriting existing content

The vulnerability manifests in the frame parsing and export functionality. For technical details and proof-of-concept information, see the Huntr Vulnerability Report.

Detection Methods for CVE-2024-5986

Indicators of Compromise

• Unexpected modifications to critical system files such as SSH keys, crontab, or system scripts
• Unusual API requests to /3/Parse or /3/Frames/*/export endpoints with suspicious path parameters
• File writes by the H2O-3 process to locations outside the expected data directories
• New or modified files in sensitive directories that correlate with H2O-3 service activity

Detection Strategies

• Monitor HTTP requests to H2O-3 API endpoints for path traversal patterns (e.g., ../, absolute paths)
• Implement file integrity monitoring on critical system files and directories
• Set up alerting for H2O-3 process file operations outside designated data directories
• Review web server and application logs for anomalous export endpoint usage patterns

Monitoring Recommendations

• Enable verbose logging for H2O-3 API endpoints and monitor for suspicious activity
• Deploy endpoint detection and response (EDR) solutions to monitor file system changes
• Configure network intrusion detection to alert on exploitation attempts targeting the Parse and Export endpoints
• Establish baseline behavior for the H2O-3 service and alert on deviations

How to Mitigate CVE-2024-5986

Immediate Actions Required

• Restrict network access to H2O-3 instances to trusted networks only
• Place H2O-3 behind an authenticated reverse proxy to prevent unauthorized access
• Run the H2O-3 service with minimal filesystem permissions using a dedicated low-privilege user account
• Implement application-level firewalls to filter malicious API requests

Patch Information

Consult the H2O-3 project for updated versions that address this vulnerability. Review the Huntr Vulnerability Report for additional remediation guidance and check the official h2oai/h2o-3 repository for security patches or updated releases.

Workarounds

• Isolate H2O-3 instances in containers or virtual machines with restricted filesystem access
• Configure read-only filesystem mounts for sensitive directories
• Implement strict network segmentation to limit exposure of the H2O-3 API
• Use mandatory access control systems (SELinux, AppArmor) to restrict file write operations

# Example: Restrict H2O-3 service to dedicated user with limited permissions
# Create dedicated service user
useradd -r -s /bin/false h2o-service

# Restrict directory permissions
chown -R h2o-service:h2o-service /opt/h2o-3/data
chmod 700 /opt/h2o-3/data

# Run H2O-3 with restricted user
sudo -u h2o-service java -jar /opt/h2o-3/h2o.jar