---
id: CVE-2026-100302
title: >-
  Apache ZooKeeper: Denial of service through unbounded memory allocation in
  multiRead request handling
summary: >-
  Allocation of Resources Without Limits or Throttling in the multiRead request
  handler of Apache ZooKeeper allows a remote attacker to crash the server
  (denial of service) with a single small request.


  The multiRead handler places no limi…
severity: high
cvss: 7.1
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'
cvssSource: cna
cwe:
  - CWE-770
vendor: Apache Software Foundation
product: 'org.apache.zookeeper:zookeeper'
affected:
  - 'org.apache.zookeeper:zookeeper >= 3.9.0 <= 3.9.6'
  - 'org.apache.zookeeper:zookeeper >= 3.8.0 <= 3.8.7'
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-04T14:34:46.610023Z'
published: '2026-11-04'
updated: '2026-11-04'
sourceUpdated: '2026-11-04T15:18:55.017Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-100302'
references:
  - url: 'https://lists.apache.org/thread.html/gj2vxwx8myq31js6tvb7bgls4nnxohj7'
tags:
  - cve.org
ingestedAt: '2026-11-05T21:36:00.421Z'
---

## Overview

Allocation of Resources Without Limits or Throttling in the multiRead request handler of Apache ZooKeeper allows a remote attacker to crash the server (denial of service) with a single small request.

The multiRead handler places no limit on the number of bundled read operations or on the cumulative size of the response it builds in memory. Because each operation's result is fully materialized and retained before serialization, a request that is small on the wire — within the jute.maxbuffer limit — but that references a large znode many times can force the server to allocate far more heap than the request size implies, exhausting the JVM heap and terminating the server with an OutOfMemoryError. Neither jute.maxbuffer nor largeRequestMaxBytes prevents this, as both bound only the inbound request, not the response.

This issue affects Apache ZooKeeper from 3.7.0 through 3.9.6. Users are recommended to upgrade to version 3.9.7, which enforces configurable limits on the multiRead operation count and cumulative response size.

## Affected

- `org.apache.zookeeper:zookeeper >= 3.9.0 <= 3.9.6`
- `org.apache.zookeeper:zookeeper >= 3.8.0 <= 3.8.7`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.