CVE-2026-59969Network attack vectorHinoki check available

Quorum infiltration via skipped TLS hostname verification

Published Sep 16, 2026 · Updated Sep 16, 2026

Improper certificate validation in Apache ZooKeeper 3.8.0 through 3.8.6 and 3.9.0 through 3.9.5 allows attackers to join quorum traffic. The Java SSLSocket quorum path accepts a CA-trusted peer certificate even when its subject alternative name does not match the connected host. The flaw is reachable only when quorum TLS, FIPS mode, and both quorum hostname-verification settings are enabled, allowing an untrusted peer with a trusted certificate to enter elections and replication flows.

CVSS severityUnavailable
Unscored
EPSS probability0.12%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Improper certificate validation in Apache ZooKeeper 3.8.0 through 3.8.6 and 3.9.0 through 3.9.5 allows attackers to join quorum traffic. The Java SSLSocket quorum path accepts a CA-trusted peer certificate even when its subject alternative name does not match the connected host. The flaw is reachable only when quorum TLS, FIPS mode, and both quorum hostname-verification settings are enabled, allowing an untrusted peer with a trusted certificate to enter elections and replication flows.

The record

CVE
CVE-2026-59969
Published
Sep 16, 2026
Updated
Sep 16, 2026
Vendor
The Apache Software Foundation
Product
Apache ZooKeeper
Classifications
T1557
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 16, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=3.8.0 <=3.8.6
  2. Affected versionversion=3.9.0 <=3.9.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

The Apache Software Foundation · Apache ZooKeeperversion=3.8.0 <=3.8.6; version=3.9.0 <=3.9.5

Published CVSS scores

No CVSS assessment is available in this record.

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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