# CVE-2026-59739: Apache ZooKeeper information disclosure in SetWatches reconnect replay

Source: https://junglewise.ai/threats/cve-2026-59739-apache-zookeeper-information-disclosure-in-setwatches-reconnect  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-16. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-59739 · Severity: high · CVSS 7.5 · Published 2026-09-16

Apache ZooKeeper is a distributed coordination service used to manage configuration and synchronization in distributed systems. An incomplete security fix allows an attacker to discover the names of ACL-restricted data paths by exploiting the SetWatches reconnect replay mechanism. While the actual data stored in these paths remains protected, the path names themselves can expose sensitive information such as usernames or login IDs.

Technologies: [Apache Zookeeper](https://junglewise.ai/threats/technologies/zookeeper). Vendors: [Apache](https://junglewise.ai/threats/vendors/apache).

## Quick answers

**Is CVE-2026-59739 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59739 being exploited in the wild.

**How severe is CVE-2026-59739?** High severity, with a CVSS score of 7.5, published 16 September 2026.

**Which products and versions are affected?** Apache Zookeeper prior to 3.8.7 and 3.9.6.

**Is there a fix for CVE-2026-59739?** A patch was published on 2026-09-16: Patches available in versions 3.8.7 and 3.9.6 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-59739 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-59739?** Check whether you run Apache Zookeeper at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is a missing ACL (Access Control List) check in the SetWatches reconnect replay handler. It stems from an incomplete fix to CVE-2024-23944: while the fix added ACL validation to WatchManager.triggerWatch(), the vulnerable DataTree.setWatches() method still calls watcher.process(event) with null ACL context, bypassing the check entirely. An attacker can exploit this by registering exists-watches on non-existent paths, then reconnecting after those paths are created with restricted ACLs—the ZooKeeper server will replay the watch events without proper ACL validation, exposing the path names to the connecting client. The attack requires the ability to connect to ZooKeeper as a client; no data contents are leaked, only the path names. Patches are available in versions 3.9.6 and 3.8.7.

## Affected products

- Apache ZooKeeper prior to 3.8.7 and 3.9.6

## Timeline

- 2026-09-16: disclosed
- 2026-09-16: patched: Patches available in versions 3.8.7 and 3.9.6

## References

- [https://repo.maven.apache.org/maven2](https://repo.maven.apache.org/maven2)
- [https://lists.apache.org/thread/v0lrwsbdxvx6w67p3z7fxf3hzyncq55l](https://lists.apache.org/thread/v0lrwsbdxvx6w67p3z7fxf3hzyncq55l)

## Related threats

- [Apache ZooKeeper uncontrolled recursion in snapshot serialization](https://junglewise.ai/threats/cve-2026-115448-uncontrolled-recursion-in-apache-zookeeper-the-server-serializes)
- [Apache ZooKeeper denial of service in multiRead handler](https://junglewise.ai/threats/cve-2026-100302-allocation-of-resources-without-limits-or-throttling-in-the)
- [Apache ZooKeeper quota subsystem denial of service](https://junglewise.ai/threats/cve-2026-100300-improper-handling-of-exceptional-conditions-in-the-quota)
- [Apache ZooKeeper improper authorization in SASL authentication](https://junglewise.ai/threats/cve-2026-100252-improper-authorization-vulnerability-in-apache-zookeeper-when)
- [Apache ZooKeeper setACL time-of-check time-of-use race condition](https://junglewise.ai/threats/cve-2026-100235-incorrect-authorization-due-to-a-time-of-check-to-time-of-use)