CVE-2026-59969
Received Received - Intake

Apache ZooKeeper Quorum TLS Hostname Verification Bypass in FIPS Mode

Publication date: 2026-09-16

Last updated on: 2026-09-16

Assigner: Apache Software Foundation

Description
Apache ZooKeeper quorum TLS fails to enforce peer hostname verification in FIPS-mode deployments. When sslQuorum=true, zookeeper.fips-mode=true, ssl.quorum.hostnameVerification=true, and ssl.quorum.clientHostnameVerification=true are enabled, the Java SSLSocket quorum path accepts a CA-trusted peer certificate whose SAN does not match the connected host. A malicious or misissued peer certificate can therefore join quorum traffic, participate in leader election, and enter replication flows. Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.

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Meta Information

Published
2026-09-16
Last Modified
2026-09-16
Generated
2026-09-16
AI Q&A
2026-09-16
EPSS Evaluated
N/A
NVD
CVE-2026-59969
EUVD
EUVD-2026-80331

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
apache zookeeper 3.8.7
apache zookeeper 3.9.6

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-297 The product communicates with a host that provides a certificate, but the product does not properly ensure that the certificate is actually associated with that host.

Attack-Flow Graph

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Executive Summary

This vulnerability affects Apache ZooKeeper in FIPS-mode deployments where TLS is used for quorum communication. When specific SSL settings are enabled, the system fails to verify that a peer's certificate Subject Alternative Name (SAN) matches the connected host. This allows a malicious or misissued certificate to join the quorum, participate in leader election, and replicate data.

Impact Analysis

If exploited, this vulnerability could allow unauthorized nodes to join the ZooKeeper cluster, potentially leading to data breaches, unauthorized access to sensitive data, or disruption of cluster operations. It undermines the integrity and security of the distributed system.

Compliance Impact

This vulnerability could lead to non-compliance with GDPR, HIPAA, and other regulations that require strict access controls and data integrity. Unauthorized access to quorum traffic may result in data exposure or tampering, violating confidentiality and integrity requirements.

Mitigation Strategies

Upgrade Apache ZooKeeper to version 3.8.7 or 3.9.6 to fix the issue.

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