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OpenSearch has ineffective TLS certificate hostname verification

Low severity GitHub Reviewed Published Apr 30, 2026 in opensearch-project/security • Updated May 7, 2026

Package

maven org.opensearch.plugin:opensearch-security (Maven)

Affected versions

>= 2.18.0, < 2.19.4.0
>= 3.0.0, < 3.3.0.0

Patched versions

2.19.4.0
3.3.0.0

Description

Description

A regression was introduced in OpenSearch 2.18.0 that caused the plugins.security.ssl.transport.enforce_hostname_verification setting to be ineffective. When this setting was enabled, OpenSearch did not verify that the hostname in a connecting node's TLS certificate matched the hostname of the connection. This could allow a node with a valid certificate (signed by the cluster's trusted CA) but an incorrect hostname SAN to join the cluster.

Impact

Clusters running affected versions with hostname verification enabled did not receive the expected protection from this setting. A node presenting a certificate signed by the cluster's trusted CA could join the cluster regardless of whether its hostname SAN matched. This regression does not affect certificate validation itself — only the additional hostname verification check.

Patches

This issue is fixed in OpenSearch 2.19.4 and 3.3.0.

Workarounds

Use more restrictive values for plugins.security.nodes_dn to limit which certificates are accepted for node-to-node communication.

References

@cwperks cwperks published to opensearch-project/security Apr 30, 2026
Published to the GitHub Advisory Database May 7, 2026
Reviewed May 7, 2026
Last updated May 7, 2026

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
High
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:N

EPSS score

Weaknesses

Improper Certificate Validation

The product does not validate, or incorrectly validates, a certificate. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-x5hg-x4gv-j98m

Source code

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