Severity: important
CVSS 4.0: 7.1 (high)
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
Affected versions:
- Apache ZooKeeper 3.9.0 through 3.9.6
- Apache ZooKeeper 3.8.0 through 3.8.7
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.
References:
https://zookeeper.apache.org/
https://www.cve.org/CVERecord?id=CVE-2026-100302
