Apache ZooKeeper neutralization for logs

Summaryinfo

A vulnerability identified as critical has been detected in Apache ZooKeeper. The impacted element is an unknown function. This manipulation causes neutralization for logs. This vulnerability is registered as CVE-2026-84439. Remote exploitation of the attack is possible. No exploit is available.

Detailsinfo

A vulnerability has been found in Apache ZooKeeper (affected version not known) and classified as critical. Affected by this vulnerability is some unknown functionality. The manipulation with an unknown input leads to a neutralization for logs vulnerability. The CWE definition for the vulnerability is CWE-117. The product does not neutralize or incorrectly neutralizes output that is written to logs. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

This vulnerability is known as CVE-2026-84439. The exploitation appears to be easy. The attack can be launched remotely. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 09/21/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Vendor

• Apache

Name

• ZooKeeper

License

• open-source

Website

• Vendor: https://www.apache.org/

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