Release Notes - ZooKeeper - Version 3.9.5

Sub-task

• ZOOKEEPER-842 - stat calls static method on org.apache.zookeeper.server.DataTree

Bug

• ZOOKEEPER-4736 - socket fd leak
• ZOOKEEPER-4871 - ZooKeeper python module (zkpython) is incompatible with Python 3.12
• ZOOKEEPER-4958 - "ssl.clientHostnameVerification" is ignored if "ssl.authProvider" is configured to "x509"
• ZOOKEEPER-4974 - Remove enforced JDK 17 compilation warnings
• ZOOKEEPER-4984 - Upgrade OWASP plugin to 12.1.6 due to breaking changes in the API
• ZOOKEEPER-4986 - Disable reverse DNS lookup in TLS client and server
• ZOOKEEPER-4989 - Compilation of client on Windows with MSVC is broken

Improvement

• ZOOKEEPER-3938 - Upgrade jline to version 3.x.
• ZOOKEEPER-4955 - Fix interference with jvm ssl properties for ssl.crl and ssl.ocsp
• ZOOKEEPER-4962 - Add getPort and getSecurePort for ZooKeeperServerEmbedded
• ZOOKEEPER-4965 - Drop unnecessary @SuppressWarnings("deprecation")
• ZOOKEEPER-4970 - Deprecate methods of ZKConfig which throw QuorumPeerConfig.ConfigException

Test

• ZOOKEEPER-4780 - Avoid creating temporary files in source directory.

Task

• ZOOKEEPER-4976 - Update Netty to fix CVE-2025-58057
• ZOOKEEPER-5017 - Upgrade Netty to 4.1.130.Final to address CVE-2025-67735
• ZOOKEEPER-5018 - Upgrade Jetty to 9.4.58.v20250814 in order to fix CVE-2025-5115

---

Release Notes - ZooKeeper - Version 3.9.4

Breaking Changes

ZOOKEEPER-4891 updates logback-classic to 1.3.15 to solve CVE issues and slf4j-api to 2.0.13 to meet the compatibility requirement of logback.

This could cause slf4j to complain "No SLF4J providers were found" and output no further logs in certain conditions:

1. For library or client usage, this could happen if you specify and inherit incompatible slf4j and logback versions, say, slf4j-api:2.0.13 from org.apache.zookeeper:zookeeper and logback-classic:1.2.13 from customized project dependencies.
2. For application or deployment usage, this could happen if you custom and inherit incompatible slf4j and logback versions in classpath, say, slf4j-api:2.0.13 from zookeeper distribution and logback-classic:1.2.13 from customization.

This can be resolved by specifying compatible slf4j and logback versions in classpath, say, slf4j-api:2.0.13 and logback-classic:1.3.15.

Bug

• ZOOKEEPER-4020 - Memory leak in Zookeeper C Client
• ZOOKEEPER-4240 - IPV6 support in ZooKeeper ACL
• ZOOKEEPER-4604 - Creating a COMPLETION_STRING_STAT would set acl_result completion
• ZOOKEEPER-4699 - zh->hostname heap-use-after-free in zookeeper_interest
• ZOOKEEPER-4725 - TTL node creations do not appear in audit log
• ZOOKEEPER-4787 - Failed to establish connection between zookeeper
• ZOOKEEPER-4810 - Fix data race in format_endpoint_info()
• ZOOKEEPER-4819 - Can't seek for writable tls server if connected to readonly server
• ZOOKEEPER-4846 - Failure to reload database due to missing ACL
• ZOOKEEPER-4848 - Possible stack overflow in setup_random
• ZOOKEEPER-4858 - Remove the lock contention between snapshotting and the sync operation
• ZOOKEEPER-4872 - SnapshotCommand should not perform fastForwardFromEdits
• ZOOKEEPER-4886 - observer with small myid can't join SASL quorum
• ZOOKEEPER-4889 - Fallback to DIGEST-MD5 auth mech should be disabled in Fips mode
• ZOOKEEPER-4900 - Bump patch release of jetty to include CVE fix for CVE-2024-6763
• ZOOKEEPER-4907 - Shouldn't throw "Len error" when server closing cause confusion
• ZOOKEEPER-4909 - When a spurious wakeup occurs, the client's waiting time may exceed requestTimeout.
• ZOOKEEPER-4919 - ResponseCache supposed to be a LRU cache
• ZOOKEEPER-4921 - Zookeeper Client 3.9.3 Fails to Reconnect After Network Failures
• ZOOKEEPER-4925 - Diff sync introduce hole in stale follower's committedLog which cause data loss in leading
• ZOOKEEPER-4928 - Version in zookeeper_version.h is not updated
• ZOOKEEPER-4933 - Connection throttle exception causing all connections to be rejected
• ZOOKEEPER-4940 - Enabling zookeeper.ssl.ocsp with JRE TLS provider errors out
• ZOOKEEPER-4953 - Fixing Typo In ZooKeeper Programmer's Guide
• ZOOKEEPER-4960 - Upgrade OWASP plugin to 12.1.3 due to recent parsing errors

New Feature

• ZOOKEEPER-4895 - Introduce a helper function for C client to generate password for SASL authentication

Improvement

• ZOOKEEPER-4790 - TLS Quorum hostname verification breaks in some scenarios
• ZOOKEEPER-4852 - Fix the bad "*uuuuu" mark in the ASF license
• ZOOKEEPER-4891 - Update logback to 1.3.15 to fix CVE-2024-12798.
• ZOOKEEPER-4902 - Document that read-only mode also enables isro 4lw
• ZOOKEEPER-4906 - Log full exception details for server JAAS config failure
• ZOOKEEPER-4944 - Cache zookeeper dists for end to end compatibility tests
• ZOOKEEPER-4954 - Use FIPS style hostname verification when no custom truststore is specified
• ZOOKEEPER-4964 - Check permissions individually during admin server auth

Task

• ZOOKEEPER-4897 - Upgrade Netty to fix CVE-2025-24970 in ZooKeeper 3.9.3
• ZOOKEEPER-4959 - Fix license files after logback/slf4j upgrade

---

Release Notes - ZooKeeper - Version 3.9.3

Bug

• ZOOKEEPER-2332 - Zookeeper failed to start for empty txn log
• ZOOKEEPER-2623 - CheckVersion outside of Multi causes NullPointerException
• ZOOKEEPER-4293 - Lock Contention in ClientCnxnSocketNetty (possible deadlock)
• ZOOKEEPER-4394 - Learner.syncWithLeader got NullPointerException
• ZOOKEEPER-4409 - NullPointerException in SendAckRequestProcessor
• ZOOKEEPER-4508 - ZooKeeper client run to endless loop in ClientCnxn.SendThread.run if all server down
• ZOOKEEPER-4712 - Follower.shutdown() and Observer.shutdown() do not correctly shutdown the syncProcessor, which may lead to data inconsistency
• ZOOKEEPER-4733 - non-return function error and asan error in CPPUNIT TESTs
• ZOOKEEPER-4752 - Remove version files in zookeeper-server/src/main from .gitignore
• ZOOKEEPER-4804 - Use daemon threads for Netty client
• ZOOKEEPER-4814 - Protocol desynchronization after Connect for (some) old clients
• ZOOKEEPER-4839 - When DigestMD5 is used to enable mandatory client authentication, users that do not exist can log in
• ZOOKEEPER-4843 - Encountering an 'Unreasonable Length' error when configuring jute.maxbuffer to 1GB or more
• ZOOKEEPER-4876 - jetty-http-9.4.53.v20231009.jar: CVE-2024-6763(3.7)

New Feature

• ZOOKEEPER-4747 - Java api lacks synchronous version of sync() call

Improvement

• ZOOKEEPER-4850 - Enhance zkCli Tool to Support Reading and Writing Binary Data
• ZOOKEEPER-4851 - Honor X-Forwarded-For optionally in IPAuthenticationProvider
• ZOOKEEPER-4860 - Disable X-Forwarded-For in IPAuthenticationProvider by default

Test

• ZOOKEEPER-4859 - C client tests hang to be cancelled quite often

Task

• ZOOKEEPER-4820 - zookeeper pom leaks logback dependency
• ZOOKEEPER-4868 - Bump commons-io library to 2.14.0

---

Release Notes - ZooKeeper - Version 3.9.2

Sub-task

• ZOOKEEPER-910 - Use SelectionKey.isXYZ() methods instead of complicated binary logic
• ZOOKEEPER-4728 - Zookeeper cannot bind to itself forever if DNS is not ready when startup

Bug

• ZOOKEEPER-2590 - exists() should check read ACL permission
• ZOOKEEPER-4236 - Java Client SendThread create many unnecessary Login objects
• ZOOKEEPER-4415 - Zookeeper 3.7.0 : The client supported protocol versions [TLSv1.3] are not accepted by server preferences
• ZOOKEEPER-4730 - Incorrect datadir and logdir size reported from admin and 4lw dirs command
• ZOOKEEPER-4785 - Txn loss due to race condition in Learner.syncWithLeader() during DIFF sync

Improvement

• ZOOKEEPER-3486 - add the doc about how to configure SSL/TLS for the admin server
• ZOOKEEPER-4756 - Merge script should use GitHub api to merge pull requests
• ZOOKEEPER-4778 - Patch jetty, netty, and logback to remove high severity vulnerabilities
• ZOOKEEPER-4794 - Reduce the ZKDatabase#committedLog memory usage
• ZOOKEEPER-4799 - Refactor ACL check in addWatch command
• ZOOKEEPER-4801 - Add memory size limitation policy for ZkDataBase#committedLog

Wish

• ZOOKEEPER-4807 - Add sid for the leader goodbye log

---

Release Notes - ZooKeeper - Version 3.9.1

Improvement

• ZOOKEEPER-4732 - improve Reproducible Builds
• ZOOKEEPER-4753 - Explicit handling of DIGEST-MD5 vs GSSAPI in quorum auth

Task

• ZOOKEEPER-4751 - Update snappy-java to 1.1.10.5 to address CVE-2023-43642
• ZOOKEEPER-4754 - Update Jetty to avoid CVE-2023-36479, CVE-2023-40167, and CVE-2023-41900
• ZOOKEEPER-4755 - Handle Netty CVE-2023-4586

---

Release Notes - ZooKeeper - Version 3.9.0

Sub-task

• ZOOKEEPER-4327 - Flaky test: RequestThrottlerTest

Bug

• ZOOKEEPER-2108 - Compilation error in ZkAdaptor.cc with GCC 4.7 or later
• ZOOKEEPER-3652 - Improper synchronization in ClientCnxn
• ZOOKEEPER-3908 - zktreeutil multiple issues
• ZOOKEEPER-3996 - Flaky test: ReadOnlyModeTest.testConnectionEvents
• ZOOKEEPER-4026 - CREATE2 requests embedded in a MULTI request only get a regular CREATE response
• ZOOKEEPER-4296 - NullPointerException when ClientCnxnSocketNetty is closed without being opened
• ZOOKEEPER-4308 - Flaky test: EagerACLFilterTest.testSetDataFail
• ZOOKEEPER-4393 - Problem to connect to zookeeper in FIPS mode
• ZOOKEEPER-4466 - Support different watch modes on same path
• ZOOKEEPER-4471 - Remove WatcherType.Children break persistent watcher's child events
• ZOOKEEPER-4473 - zooInspector create root node fail with path validate
• ZOOKEEPER-4475 - Persistent recursive watcher got NodeChildrenChanged event
• ZOOKEEPER-4477 - Single Kerberos ticket renewal failure can prevent all future renewals since Java 9
• ZOOKEEPER-4504 - ZKUtil#deleteRecursive causing deadlock in HDFS HA functionality
• ZOOKEEPER-4505 - CVE-2020-36518 - Upgrade jackson databind to 2.13.2.1
• ZOOKEEPER-4511 - Flaky test: FileTxnSnapLogMetricsTest.testFileTxnSnapLogMetrics
• ZOOKEEPER-4514 - ClientCnxnSocketNetty throwing NPE
• ZOOKEEPER-4515 - ZK Cli quit command always logs error
• ZOOKEEPER-4537 - Race between SyncThread and CommitProcessor thread
• ZOOKEEPER-4549 - ProviderRegistry may be repeatedly initialized
• ZOOKEEPER-4565 - Config watch path get truncated abnormally and fail chroot zookeeper client
• ZOOKEEPER-4647 - Tests don't pass on JDK20 because we try to mock InetAddress
• ZOOKEEPER-4654 - Fix C client test compilation error in Util.cc.
• ZOOKEEPER-4674 - C client tests don't pass on CI
• ZOOKEEPER-4719 - Use bouncycastle jdk18on instead of jdk15on
• ZOOKEEPER-4721 - Upgrade OWASP Dependency Check to 8.3.1

New Feature

• ZOOKEEPER-4570 - Admin server API for taking snapshot and stream out the data
• ZOOKEEPER-4655 - Communicate the Zxid that triggered a WatchEvent to fire

Improvement

• ZOOKEEPER-3731 - Disable HTTP TRACE Method
• ZOOKEEPER-3806 - TLS - dynamic loading for client trust/key store
• ZOOKEEPER-3860 - Avoid reverse DNS lookup for hostname verification when hostnames are provided in the connection url
• ZOOKEEPER-4289 - Reduce the performance impact of Prometheus metrics
• ZOOKEEPER-4303 - ZooKeeperServerEmbedded could auto-assign and expose ports
• ZOOKEEPER-4464 - zooinspector display "Ephemeral Owner" in hex for easy match to jmx session
• ZOOKEEPER-4467 - Missing op code (addWatch) in Request.op2String
• ZOOKEEPER-4472 - Support persistent watchers removing individually
• ZOOKEEPER-4474 - ZooDefs.opNames is unused
• ZOOKEEPER-4490 - Publish Clover results to SonarQube
• ZOOKEEPER-4491 - Adding SSL support to Zktreeutil
• ZOOKEEPER-4492 - Merge readOnly field into ConnectRequest and Response
• ZOOKEEPER-4494 - Fix error message format
• ZOOKEEPER-4518 - remove useless log in the PrepRequestProcessor#pRequest method
• ZOOKEEPER-4519 - Testable interface should have a testableCloseSocket() method
• ZOOKEEPER-4529 - Upgrade netty to 4.1.76.Final
• ZOOKEEPER-4531 - Revert Netty TCNative change
• ZOOKEEPER-4551 - Do not log spammy stacktrace when a client closes its connection
• ZOOKEEPER-4566 - Create tool for recursive snapshot analysis
• ZOOKEEPER-4573 - Encapsulate request bytebuffer in Request
• ZOOKEEPER-4575 - ZooKeeperServer#processPacket take record instead of bytes
• ZOOKEEPER-4616 - Upgrade docker image for the dev environment to resolve CVEs
• ZOOKEEPER-4622 - Add Netty-TcNative OpenSSL Support
• ZOOKEEPER-4636 - Fix zkServer.sh for AIX
• ZOOKEEPER-4657 - Publish SBOM artifacts
• ZOOKEEPER-4659 - Upgrade Commons CLI to 1.5.0 due to OWASP failing on 1.4 CVE-2021-37533
• ZOOKEEPER-4660 - Suppress false positive OWASP failure for CVE-2021-37533
• ZOOKEEPER-4661 - Upgrade Jackson Databind to 2.13.4.2 for CVE-2022-42003 CVE-2022-42004
• ZOOKEEPER-4705 - Restrict GitHub merge button to allow squash commit only
• ZOOKEEPER-4717 - Cache serialize data in the request to avoid repeat serialize.
• ZOOKEEPER-4718 - Removing unnecessary heap memory allocation in serialization can help reduce GC pressure.

Test

• ZOOKEEPER-4630 - Fix the NPE from ConnectionMetricsTest.testRevalidateCount
• ZOOKEEPER-4676 - ReadOnlyModeTest doesn't compile on JDK20 (Thread.suspend has been removed)

Wish

• ZOOKEEPER-3615 - write a TLA+ specification to verify Zab protocol
• ZOOKEEPER-4710 - Fix ZkUtil deleteInBatch() by releasing semaphore after set flag
• ZOOKEEPER-4714 - Improve syncRequestProcessor performance
• ZOOKEEPER-4715 - Verify file size and position in testGetCurrentLogSize.

Task

• ZOOKEEPER-4479 - Tests: C client test TestOperations.cc testTimeoutCausedByWatches1 is very flaky on CI
• ZOOKEEPER-4482 - Fix LICENSE FILES for commons-io and commons-cli
• ZOOKEEPER-4599 - Upgrade Jetty to avoid CVE-2022-2048
• ZOOKEEPER-4641 - GH CI fails with error: implicit declaration of function FIPS_mode
• ZOOKEEPER-4642 - Remove Travis CI
• ZOOKEEPER-4649 - Upgrade netty to 4.1.86 because of CVE-2022-41915
• ZOOKEEPER-4669 - Upgrade snappy-java to 1.1.9.1 (in order to support M1 macs)
• ZOOKEEPER-4688 - Upgrade cyclonedx-maven-plugin to 2.7.6
• ZOOKEEPER-4700 - Update Jetty for fixing CVE-2023-26048 and CVE-2023-26049
• ZOOKEEPER-4707 - Update snappy-java to address multiple CVEs
• ZOOKEEPER-4709 - Upgrade Netty to 4.1.94.Final
• ZOOKEEPER-4716 - Upgrade jackson to 2.15.2, suppress two false positive CVE errors