CVE-2026-84439: When audit logging is enabled (zookeeper.audit.enable=true), an unauthenticated attacker can inject arbitrary

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MEDIUM 5.3REMOTEWATCHLISTUPGRADE

CVE-2026-84439 is a medium-severity flaw (CVSS 5.3) affecting zookeeper. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 46%)
CISA exploited list	No
Weakness	CWE-117
Published	2026-09-16
Last modified	2026-09-18

Publisher (CNA): Apache Software Foundation · Vendor: apache

Last updated 2026-09-18 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-16 10:16 UTCPublished CVE record published
2026-09-18 14:37 UTCUpdated Record last modified

apache zookeeper UPGRADE

Affected: >= 3.8.0 and < 3.8.7 · >= 3.9.0 and < 3.9.6

Fixed in: 3.8.7, 3.9.6

Safe to downgrade to: a release before 3.8.0

1. Check installed version

apt-cache policy zookeeper || rpm -q zookeeper || zookeeper --version

2. UPGRADE to 3.8.7 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade zookeeper

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade zookeeper

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 3.8.0 (Debian / Ubuntu)

apt-cache madison zookeeper sudo apt install zookeeper=<VERSION_BEFORE_3.8.0> sudo apt-mark hold zookeeper

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list zookeeper sudo dnf downgrade zookeeper-<VERSION_BEFORE_3.8.0> sudo dnf versionlock add zookeeper

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-84439?

zookeeper: upgrade to 3.8.7, 3.9.6. Exact commands for each OS are on this page.

Is CVE-2026-84439 being exploited?

CVE-2026-84439 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-84439 affect?

CVE-2026-84439 affects zookeeper. Severity is medium (CVSS 5.3). 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 usern

How urgent is CVE-2026-84439?

Priority 42/100. Remotely exploitable, no login, no user action; On your watchlist

Software pages

Apache ZooKeeper vulnerabilities

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References

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