⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● Medium · CVSS 5.9

How to Fix CVE-2026-3960: CWE-94 Improper Control of Generation of Code in h2oai/h2o-3

By Sai Kiran Pandrala

Other vulnerabilities in the same area that are worth patching alongside this one:

Last verified: 2026-05-25

CVE-2026-3960 is a cwe-94 improper control of generation of code in h2oai h2oai/h2o-3. Fix it by upgrading to the patched build from the vendor advisory.

⚡ At a glance
SeverityCVSS 5.9 - Medium
Actively exploited?Not currently in the CISA KEV catalog
Affectedh2oai/h2o-3 unspecified up to (excluding) 3.46.0.10
Fixed inSee vendor advisory
Type (CWE)CWE-94: CWE-94 Improper Control of Generation of Code

What is CVE-2026-3960?

CVE-2026-3960 is a cwe-94 improper control of generation of code flaw in h2oai h2oai/h2o-3. It carries a CVSS base score of 5.9 (medium). It is not currently listed in the CISA Known Exploited Vulnerabilities catalog.

From the source record: 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.

Why it matters in practice: The blast radius depends on how the affected service is exposed. An internet-facing instance with no compensating controls is the highest-risk configuration.

Am I affected?

You are affected if your installation of h2oai/h2o-3 matches a version listed in the Affected row above.

Check the running version against the Affected row above using the product's admin console or --version flag.

How to fix CVE-2026-3960

Apply the vendor patch. Target the build named in the Fixed in row above (See vendor advisory). The runnable command set below covers the most common deployment patterns for h2oai/h2o-3.

Generic upgrade pattern

If the affected product is a Linux package, upgrade via the system package manager:


# Debian / Ubuntu
sudo apt-get update && sudo apt-get upgrade -y

# RHEL / Rocky / Alma
sudo dnf upgrade --security -y

If it ships as a Windows installer, download the patched build from the vendor advisory and:


# Vendor advisory: https://huntr.com/bounties/6954fe04-b905-453f-8c53-205ac8377e0d
Start-Process msiexec.exe -ArgumentList '/i <patched-installer>.msi /qn /norestart' -Wait
Get-ItemProperty HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\* | \
    Where-Object DisplayName -match '<product-name>' | Select-Object DisplayName, DisplayVersion

After applying the patch

  1. Restart the service or device so the patched binary loads.
  2. Confirm the running version matches the Fixed in row using the verification command below.
  3. Rotate credentials and API keys that the affected service could access if the asset was exposed during the disclosure window.

If you can't patch immediately

Until the patch lands, narrow the attack surface with these runnable controls.

Restrict network exposure

Block public access to the affected service at the perimeter. Allow only trusted source IPs.


# Linux iptables: only allow trusted admin subnet
sudo iptables -A INPUT -p tcp --dport 443 -s 10.10.10.0/24 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 443 -j DROP
sudo iptables-save | sudo tee /etc/iptables/rules.v4


# Windows firewall: only allow trusted admin subnet on management port
New-NetFirewallRule -DisplayName "Restrict-Mgmt-Allow" -Direction Inbound -Action Allow `
  -RemoteAddress 10.10.10.0/24 -Protocol TCP -LocalPort 443
New-NetFirewallRule -DisplayName "Restrict-Mgmt-Deny"  -Direction Inbound -Action Block `
  -Protocol TCP -LocalPort 443

Mitigations are temporary. Apply the vendor patch as soon as a maintenance window opens.

How to verify the fix worked

Confirm the patched build is the one actually running.

Check the running version against the Affected row above using the product's admin console or --version flag.

Expected: a version at or above the patched build named in the vendor advisory.

Also worth doing: pull recent log windows for indicators of compromise listed in the vendor advisory, and re-run an authenticated vulnerability scan with up-to-date signatures.

Frequently asked questions

Is CVE-2026-3960 being exploited in the wild?

As of 2026-05-25, CVE-2026-3960 is not listed in the CISA Known Exploited Vulnerabilities catalog. Watch the catalog and patch on a normal cadence; KEV status can change as exploitation evidence emerges.

What is the CVSS score for CVE-2026-3960?

The CVSS base score is 5.9 (Medium).

What version fixes this?

The vendor advisory names the patched build. See the References section.

Will a WAF or IDS rule alone close this?

No. Network filters cut down opportunistic scans but they do not remove the flaw. The vendor patch is the only durable fix.

References

*Assembled from the official vendor advisory, the NVD record, and the CISA KEV listing on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*