Apache ZooKeeper TLS Peer Hostname Verification Bypass (before 3.8.7)
CVE-2026-59969 Published on September 16, 2026
Apache ZooKeeper: Improper validation of certificate with host mismatch in FIPS mode
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.
Vulnerability Analysis
CVE-2026-59969 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, a high impact on integrity, and no impact on availability.
Weakness Type
Improper Validation of Certificate with Host Mismatch
The software communicates with a host that provides a certificate, but the software does not properly ensure that the certificate is actually associated with that host.
Products Associated with CVE-2026-59969
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Affected Versions
Apache Software Foundation Apache ZooKeeper:- Version 3.9.0, <= 3.9.5 is affected.
- Version 3.8.0, <= 3.8.6 is affected.