# CVE-2026-84439: Apache ZooKeeper audit log injection via tab characters

Source: https://junglewise.ai/threats/cve-2026-84439-apache-zookeeper-audit-log-injection-via-tab-characters  
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-2026-84439 · Severity: medium · CVSS 5.3 · Published 2026-09-16

Apache ZooKeeper is a distributed coordination service used by many enterprise applications to manage configuration and distributed system state. When audit logging is enabled, an attacker can inject forged fields into the audit log by exploiting improper escaping of tab characters in authentication and ACL data, allowing them to forge audit records and cover their tracks during incident investigations.

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

## Quick answers

**Is CVE-2026-84439 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-84439 being exploited in the wild.

**How severe is CVE-2026-84439?** Medium severity, with a CVSS score of 5.3, published 16 September 2026.

**Which products and versions are affected?** Apache Zookeeper 3.8.0 through 3.8.6, 3.9.0 through 3.9.5.

**Is there a fix for CVE-2026-84439?** A patch was published on 2026-09-16: Patch 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-2026-84439 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-84439?** 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

This is a log injection vulnerability in Apache ZooKeeper's audit logging mechanism (when zookeeper.audit.enable=true). The vulnerability exists because digest authentication usernames and ACL identifiers are serialized into the audit log without proper escaping of tab characters (\t). Since audit events use a tab-separated key=value format, an attacker can inject additional fields by embedding tabs in usernames or ACL ids, allowing them to spoof operation types (e.g., operation=delete), forge znode paths (e.g., znode=/forged), and inject fake results. The vulnerability affects versions 3.8.0–3.8.6 and 3.9.0–3.9.5; users should upgrade to 3.8.7 or 3.9.6. No public exploitation has been reported.

## Affected products

- Apache ZooKeeper 3.8.0 through 3.8.6, 3.9.0 through 3.9.5

## Timeline

- 2026-09-16: disclosed
- 2026-09-16: patched: Patch 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/b7qnjvqjh393l0j07tmnb5ggg40sx3m6](https://lists.apache.org/thread/b7qnjvqjh393l0j07tmnb5ggg40sx3m6)

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- [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)