CVE-2026-84501 Apache ZooKeeper: Operational log forgery via newline injection in EnsembleAuthenticationProvider
Unauthenticated attackers can forge log entries in Apache ZooKeeper by injecting newlines into authentication requests, misleading operators.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-84501?
CVE-2026-84501 is a medium-severity vulnerability in Apache ZooKeeper, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
An unauthenticated attacker can inject arbitrary fake log lines into Apache ZooKeeper's operational log by sending a crafted add_auth("ensemble", ...) request containing newline characters (\n). When the ensemble name doesn't match, EnsembleAuthenticationProvider.handleAuthentication() logs the raw, unsanitized name via LOG.warn(). Because SLF4J's {} placeholder preserves embedded newlines, the attacker can forge complete log entries — with arbitrary timestamps, log levels, class names, and messages — that are visually indistinguishable from genuine ZooKeeper log output.
This issue affects Apache ZooKeeper: from 3.9.0 through 3.9.5, from 3.8.0 through 3.8.6.
Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.
Weakness: CWE-117
Which versions are affected by CVE-2026-84501?
1 open source package ship an affected version, including zookeeper. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
zookeeper Bitnami | From 3.8.0 | 3.8.7, 3.9.6 |
Products include Apache Zookeeper.
How do I fix CVE-2026-84501?
Upgrade zookeeper to a fixed version for your release line: 3.8.7 or 3.9.6.
Is CVE-2026-84501 being exploited?
There is no known exploitation of CVE-2026-84501 in the wild and no public exploit code.
Other vulnerabilities in Apache ZooKeeper
- CVE-2024-51504 Apache ZooKeeper: Authentication bypass with IP-based authentication in Admin Server
- CVE-2023-44981 Apache ZooKeeper: Authorization bypass in SASL Quorum Peer Authentication
- CVE-2016-5017 Memory corruption in n/a
- CVE-2026-59739 Apache ZooKeeper: Information disclosure via SetWatches reconnect replay
- CVE-2026-59969 Apache ZooKeeper: Improper validation of certificate with host mismatch in FIPS mode
Sources
Also known as BIT-zookeeper-2026-84501, CLEANSTART-2026-KR26174, CLEANSTART-2026-QQ07895, CLEANSTART-2026-XR18271, CLEANSTART-2026-ZA11117, DEBIAN-CVE-2026-84501 and 4 more.