# CVE-2026-59969: zookeeper: Apache ZooKeeper quorum TLS fails to enforce peer hostname verification in FIPS-mode deployments

CVE-2026-59969 is fixed in zookeeper on 1 platform by DEBIAN-CVE-2026-59969 (version 3.9.6-1), released September 26, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-59969
- Priority: High
- CVSS: 7.5 (high)
- EPSS: 0.0033
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 16, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | zookeeper Debian 14 | 3.9.6-1 | [DEBIAN-CVE-2026-59969](https://patchblox.com/security/data/fix/linux/debian-cve-2026-59969.md) | Sep 26, 2026 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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