CVE-2026-84501

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.

CVSS v3 5.3 MEDIUM

5.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 3.9 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact LOW

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://lists.apache.org/thread/ohby1g6zjt72p0w79rhbr41nczzvr33y	Mailing List Vendor Advisory
http://www.openwall.com/lists/oss-security/2026/09/15/7	Mailing List

Configurations

Configuration 1 (hide)

OR	cpe:2.3:a:apache:zookeeper::::::::
	cpe:2.3:a:apache:zookeeper::::::::

History

18 Sep 2026, 14:36

Type	Values Removed	Values Added
First Time		Apache Apache zookeeper
References	~~() https://lists.apache.org/thread/ohby1g6zjt72p0w79rhbr41nczzvr33y -~~	() https://lists.apache.org/thread/ohby1g6zjt72p0w79rhbr41nczzvr33y - Mailing List, Vendor Advisory
References	~~() http://www.openwall.com/lists/oss-security/2026/09/15/7 -~~	() http://www.openwall.com/lists/oss-security/2026/09/15/7 - Mailing List
CPE		cpe:2.3:a:apache:zookeeper::::::::

16 Sep 2026, 20:17

Type	Values Removed	Values Added
CVSS	v2 : ~~unknown~~ v3 : ~~unknown~~	v2 : unknown v3 : 5.3

Information

Published : 2026-09-16 10:16

Updated : 2026-09-18 14:36

NVD link : CVE-2026-84501

Mitre link : CVE-2026-84501

CVE.ORG link : CVE-2026-84501

JSON object : View

Products Affected

apache

zookeeper

CWE

CWE-117

Improper Output Neutralization for Logs

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