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H2oApplication

CVE-2026-3960

CRITICAL · 9.8 CVSS v3.1 Published 2026-04-23
Fix available
A fix is available. Upgrade to 3.46.0.10 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A critical remote code execution vulnerability exists in the unauthenticated REST API endpoint /99/ImportSQLTable in H2O-3 version 3.46.0.9 and prior. The vulnerability arises due to insufficient security controls in the parameter blacklist mechanism, which only targets MySQL JDBC driver-specific dangerous parameters. An attacker can bypass these controls by switching the JDBC URL protocol to jdbc:postgresql: and exploiting PostgreSQL JDBC driver-specific parameters such as socketFactory and socketFactoryArg. This allows unauthenticated attackers to execute arbitrary code on the H2O-3 server with the privileges of the H2O-3 process. The issue is resolved in version 3.46.0.10.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A critical RCE vulnerability exists in H2O-3's unauthenticated /99/ImportSQLTable REST API endpoint. The parameter blacklist mechanism only blocks MySQL JDBC driver-specific dangerous parameters, but attackers bypass this by switching to PostgreSQL JDBC URL protocol (jdbc:postgresql:) and exploiting PostgreSQL-specific parameters like socketFactory and socketFactoryArg to execute arbitrary code.

MitigationUpgrade H2O-3 to version 3.46.0.10 or later. If immediate upgrade is not possible, restrict network access to the REST API endpoint.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
H2oApplication
Affected:< 3.46.0.10

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify H2O-3 installation and version
    Run 'java -jar h2o.jar -version' or check the H2O process on the system (typically runs on ports 54321/54322). The version is usually displayed in the startup output or can be found in the jar file name.
    Affected if The installed version is below 3.46.0.10 (e.g., 3.46.0.9, 3.44.x, etc.)
  2. Verify REST API is exposed
    Confirm the H2O web UI/REST API is accessible by accessing http://hostname:54321 in a browser or via curl. The /99/ endpoint is part of the internal REST API.
    Affected if The REST API is accessible without authentication on port 54321 or configured port.
  3. Check network accessibility of the API
    Attempt to reach the /99/ImportSQLTable endpoint: curl http://target:54321/99/ImportSQLTable. This endpoint is intended for internal use but may be exposed.
    Affected if The endpoint responds to requests (even with an error), indicating it is reachable.
  4. Confirm JDBC connection features are enabled
    The vulnerability affects the ImportSQLTable functionality. If SQL import features are available in your H2O deployment, the endpoint accepts jdbc: URL parameters.
    Affected if The ImportSQLTable REST endpoint accepts jdbc connection parameters in requests.

You are affected if H2O-3 version is below 3.46.0.10 AND the REST API on port 54321 is accessible over the network, allowing unauthenticated attackers to reach the /99/ImportSQLTable endpoint.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 3.46.0.10 or later
Fixed in 3.46.0.10
Vendor patch github.com →
Interim mitigation

Upgrade H2O-3 to version 3.46.0.10 or later. If immediate upgrade is not possible, restrict network access to the REST API endpoint.

Recommended fix High confidence

3.46.0.10

  1. Download H2O-3 version 3.46.0.10 from the official releases (e.g., from Maven Central or the H2O GitHub releases page)
  2. Stop any running H2O-3 instances currently running version 3.46.0.9 or earlier
  3. Replace the existing h2o.jar file with the version 3.46.0.10 JAR file
  4. Restart the H2O-3 service with the new JAR
  5. Verify the running version is 3.46.0.10 by checking the response from the /2/Cloud endpoint or the startup logs
  6. Confirm the /99/ImportSQLTable endpoint now properly blacklists PostgreSQL JDBC driver parameters (socketFactory, socketFactoryArg, etc.) in addition to MySQL parameters
Caveat Review H2O-3 release notes for version 3.46.0.10 for any behavior changes or API modifications; minor version upgrades typically have minimal breaking changes

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in H2o Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
13.0 hours of engineering $2,280
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-3960 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data