How severe is CVE-2026-3960?

CVE-2026-3960 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-3960 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (57th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-3960?

CVE-2026-3960 affects H2o. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-3960?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-3960 have an EU (EUVD) identifier?

Yes. CVE-2026-3960 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-25205.

When was CVE-2026-3960 published?

CVE-2026-3960 was published on 2026-04-23 and last updated on 2026-06-17.

CVE-2026-3960

CVE-2026-3960 is a critical-severity vulnerability in H2o with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-94.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
EPSS exploit prediction: 1% (57th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-25205
Weakness: CWE-94
Affected product: H2o
Published: 2026-04-23
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2026-3960?: 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.
How severe is CVE-2026-3960?: CVE-2026-3960 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-3960 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (57th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-3960?: CVE-2026-3960 affects H2o. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-3960?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-3960 have an EU (EUVD) identifier?: Yes. CVE-2026-3960 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-25205.
When was CVE-2026-3960 published?: CVE-2026-3960 was published on 2026-04-23 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:h2o:h2o:*:*:*:*:*:*:*:*

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