CVE-2026-100302 Apache ZooKeeper: Denial of service through unbounded memory allocation in multiRead request handling

Description

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.

Exploitable remotely over the network, with an ordinary account and without any user action; an attacker can seriously compromise confidentiality, integrity or availability.

Attack vector

Network

Attack complexity

Low

Attack requirements

None

Privileges required

Low

Interaction

None

Confidentiality

None

Integrity

None

Availability

High

Confidentiality of other systems

None

Integrity of other systems

None

Availability of other systems

None

Affected products and versions