CVE-2026-84439: When audit logging is enabled (zookeeper.audit.enable=true), an unauthenticated attacker can inject arbitrary fields into Apache ZooKeeper's audit log by…

PriorityP335medium5.3CVSS 3.1

AVNACLPRNUINSUCNILAN

EPSS

0.74%

54.2th percentile

When audit logging is enabled (zookeeper.audit.enable=true), an unauthenticated attacker can inject arbitrary fields into Apache ZooKeeper's audit log by sending a digest authentication request with tab characters (\t) embedded in the username. Because the audit log uses tab-separated key=value format, the injected tabs are parsed as legitimate field separators, allowing the attacker to spoof audit results (e.g., injecting result=success), forge operation types, and corrupt forensic evidence. A log injection vulnerability in Apache ZooKeeper allows a client that can call setACL to inject forged key-value fields into zookeeper_audit.log. When audit logging is enabled, the server serializes attacker-controlled digest ACL ids into the acl= audit field without escaping tab characters. Because audit events are emitted as tab-separated key=value records, a crafted ACL id can make one successful setAcl event appear to contain forged fields such as operation=delete and znode=/forged. This undermines the integrity of downstream audit parsing, alerting, and incident response. 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 3.9.6 or 3.8.7, which fixes the issue.

Affected

4 ranges

Vendor	Product	Version range	Fixed in
apache	zookeeper	>= 3.8.0 < 3.8.7	3.8.7
apache	zookeeper	>= 3.9.0 < 3.9.6	3.9.6
apache_software_foundation	apache_zookeeper	3.8.0 – 3.8.6	—
apache_software_foundation	apache_zookeeper	3.9.0 – 3.9.5	—

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