# CVE-2026-84501: Apache ZooKeeper log injection via crafted add_auth request

Source: https://junglewise.ai/threats/cve-2026-84501-apache-zookeeper-log-injection-via-crafted-add-auth-request  
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-2026-84501 · Severity: medium · CVSS 5.3 · Published 2026-09-16

Apache ZooKeeper is a distributed coordination service used by many enterprise systems to manage configuration and synchronization. An unauthenticated attacker can inject forged log entries that appear to be legitimate ZooKeeper operational logs, potentially misleading administrators and hindering incident investigation or compliance audits.

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

## Quick answers

**Is CVE-2026-84501 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-84501 being exploited in the wild.

**How severe is CVE-2026-84501?** 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-2026-84501?** A patch was published on 2026: Fixed 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-2026-84501 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-84501?** 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 log injection flaw in EnsembleAuthenticationProvider.handleAuthentication(). When an attacker sends a crafted add_auth("ensemble", ...) request with an ensemble name containing newline characters (\n), the unsanitized name is logged via LOG.warn() using SLF4J's {} placeholder. SLF4J does not escape embedded newlines, allowing attackers to forge complete log entries with arbitrary timestamps, log levels, class names, and messages. The attack requires no authentication and is network-reachable. Patches are available in versions 3.8.7 and 3.9.6.

## Affected products

- Apache ZooKeeper 3.8.0 through 3.8.6, 3.9.0 through 3.9.5

## Timeline

- 2026-09-16: disclosed
- 2026: patched: Fixed 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/ohby1g6zjt72p0w79rhbr41nczzvr33y](https://lists.apache.org/thread/ohby1g6zjt72p0w79rhbr41nczzvr33y)

## 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)