CVE-2026-84439: zookeeper — Fix

Description

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.

Is your site exposed to CVE-2026-84439?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

5.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS — Exploit Prediction

0.0074

Probability of exploitation

0.54%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-117 CWE-117

Affected Products

Vendor	Product	Versions
apache	zookeeper	3.8.0 — 3.8.7
apache	zookeeper	3.9.0 — 3.9.6

References

Advisories & Patches

https://lists.apache.org/thread/b7qnjvqjh393l0j07tmnb5ggg40sx3m6 http://www.openwall.com/lists/oss-security/2026/09/15/6

Frequently Asked Questions

What is 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 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. It has a CVSS v3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-84439? +

CVE-2026-84439 has a CVSS v3.1 score of 5.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0074, placing it in the 1th percentile for exploitation probability.

What products are affected by CVE-2026-84439? +

CVE-2026-84439 affects products from apache, specifically: zookeeper. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-84439? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-125125

compose-lint is a Docker Compose security linter that identifies dangerous misconfigurations before deployment. From version 0.30.0 until 0.32.0, the compose-lint …

CVE-2026-125123

compose-lint is a Docker Compose security linter that identifies dangerous misconfigurations before deployment. In version 0.31.0, compose-lint's argument parser writes …

CVE-2026-10745

Improper output neutralization for logs vulnerability in upKeeper Solutions upKeeper Instant Privilege Access on Windows allows Log Injection-Tampering-Forging. This issue …

CVE-2026-118994

CallBackery versions before 0.62.0 for Perl allow log injection via newlines in the login name. login() writes the login name …

CVE-2026-93421

Mesop is a Python-based UI framework that allows users to build web applications. Prior to 1.3.4, the unauthenticated /__csp__ endpoint …

CVE-2026-125122

compose-lint is a Docker Compose security linter that identifies dangerous misconfigurations before deployment. In version 0.31.0, compose-lint does not sanitize …