major vulnerability· requires attention

Affects widely used coordination middleware (ZooKeeper); unauthenticated crash can make nodes unbootable and disrupt distributed services.

Infrastructure

CVE-2026-100300

8.7

High

EPSS n/aPatch available

ZooKeeper quota bug allows unauthenticated writes to crash servers and corrupt on-disk data.

exploited

No known exploitation not in CISA KEV as of our last sync

fix

Patch available see the advisory in the references

likelihood

No EPSS score yet

Published 4 Nov 2026Analysed here 5 Nov 2026CVSS scored by the publisher (CNA)

common questions

Is CVE-2026-100300 being exploited?

Not confirmed. CVE-2026-100300 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked.

How severe is CVE-2026-100300?

CVE-2026-100300 is rated High with a CVSS score of 8.7. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.

Is there a patch for CVE-2026-100300?

Yes. A fix has been recorded for CVE-2026-100300. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.

What does CVE-2026-100300 affect?

CVE-2026-100300 affects Apache ZooKeeper <= 3.9.6, Default deployments with world-writable /zookeeper/quota, Clusters using ZooKeeper for coordination (Hadoop, Kafka, HBase). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.

What should I do about CVE-2026-100300?

Upgrade to 3.8.8 or 3.9.7 and tighten ACLs on /zookeeper/quota; restore from backups if needed.

Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.

executive summary

technical analysis

affected

Apache ZooKeeper <= 3.9.6Default deployments with world-writable /zookeeper/quotaClusters using ZooKeeper for coordination (Hadoop, Kafka, HBase)

impact

Unauthenticated writer to /zookeeper/quota can crash request-processing thread and render data directory permanently unbootable — service outage and possible data loss.

action required

Immediate action required

affected versions

Apache Software Foundation Apache ZooKeeper

affected>= 3.9.0 and <= 3.9.6
affected>= 3.8.0 and <= 3.8.7

As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.

cisa ssvc

exploitation: none
automatable: yes
technical impact: partial

Assessed by CISA 4 Nov 2026 (SSVC 2.0.3).

timeline

4 Nov 2026Published
4 Nov 2026CISA SSVC assessment: exploitation none · same day later
4 Nov 2026CVE record last updated · same day later
5 Nov 2026Analysed by vulneraibility.com · 1 day later

how to fix

Remediation steps are tailored for users whose stack is affected. Add this technology to your stack to see the fix checklist.

references

NVD CVE.org CVE Details Source

2 references in the CVE record: 1 advisory, 1 link

Advisorylists.apache.org /thread.html/09pgg7rcpzz44noxgtvpzstwt8fmvsb0
Linkopenwall.com /lists/oss-security/2026/11/03/11

sources

CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
NVD: CVSS and CPE data
CISA Vulnrichment (ADP): SSVC decision points
FIRST EPSS: exploit probability and percentile
Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.

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