# CVE-2026-59969: Apache ZooKeeper hostname verification bypass in FIPS-mode quorum TLS

Source: https://junglewise.ai/threats/cve-2026-59969-apache-zookeeper-hostname-verification-bypass-in-fips-mode-quorum  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-16. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-59969 · Severity: high · CVSS 7.5 · Published 2026-09-16

Apache ZooKeeper is a distributed coordination service used in many enterprise systems. When running in FIPS-mode with quorum TLS enabled and hostname verification configured, the system fails to properly validate peer certificate Subject Alternative Names (SANs), allowing an attacker with a CA-trusted certificate to impersonate legitimate cluster members, participate in leader election, and manipulate replication flows.

Technologies: [Apache Zookeeper](https://junglewise.ai/threats/technologies/zookeeper). Vendors: [Apache](https://junglewise.ai/threats/vendors/apache).

## Quick answers

**Is CVE-2026-59969 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59969 being exploited in the wild.

**How severe is CVE-2026-59969?** High severity, with a CVSS score of 7.5, published 16 September 2026.

**Which products and versions are affected?** Apache Zookeeper before 3.8.7, 3.9.x before 3.9.6.

**Is there a fix for CVE-2026-59969?** A patch was published on 2026-09-16: Patches available in ZooKeeper 3.8.7 and 3.9.6 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-59969 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-59969?** Check whether you run Apache Zookeeper at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

This vulnerability is a certificate validation bypass in ZooKeeper's Java SSLSocket implementation for quorum communication. When sslQuorum=true, zookeeper.fips-mode=true, ssl.quorum.hostnameVerification=true, and ssl.quorum.clientHostnameVerification=true are all enabled, the code fails to properly enforce SAN matching during peer authentication. An attacker can present a certificate issued by a trusted CA that lacks SAN matching the target hostname and still be accepted into the cluster. Attack vectors include network position allowing connection to quorum members. The vulnerability enables unauthorized cluster membership, leader election tampering, and replication stream injection. Fixes are available in versions 3.8.7 and 3.9.6.

## Affected products

- Apache ZooKeeper before 3.8.7, 3.9.x before 3.9.6

## Timeline

- 2026-09-16: disclosed
- 2026-09-16: patched: Patches available in ZooKeeper 3.8.7 and 3.9.6

## References

- [https://repo.maven.apache.org/maven2](https://repo.maven.apache.org/maven2)
- [https://lists.apache.org/thread/qf9kwsgtgbgtvwls6f41281846xg0rss](https://lists.apache.org/thread/qf9kwsgtgbgtvwls6f41281846xg0rss)

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