What is the CVSS score of CVE-2026-84439?

CVE-2026-84439 has a CVSS 3.1 base score of 5.3 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N. EPSS exploitation probability: 0.3%.

Zookeeper CVE-2026-84439

EUVD-2026-80333 MEDIUM

Improper Output Neutralization for Logs (CWE-117)

2026-09-15

GHSA-mxvw-9w3g-hmrq

Apache Code Injection Zookeeper

5.3

CVSS 3.1 · Vendor

View

Vulnerability Assessment

Weakness

CWE

CWE-117

OWASP Top 10:2025

A09:2025 - Security Logging & Alerting Failures

ASVS 5.0

V16 - Security Logging and Error Handling Log output neutralization

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).

No patch listed yet 0.3% exploitation probability (EPSS)

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AnalysisAIv1 – Sep 15, 2026

Audit log injection in Apache ZooKeeper 3.9.0–3.9.5 and 3.8.0–3.8.6 allows attackers to forge entries in zookeeper_audit.log when audit logging is enabled. An unauthenticated attacker can embed tab characters in a digest authentication username to inject arbitrary tab-separated key=value fields, and a client permitted to call setACL can embed tabs in a digest ACL id to make a successful setAcl event appear to record forged operations such as operation=delete and znode=/forged. The vulnerability corrupts forensic evidence and can defeat SIEM alerting, but does not permit direct modification of ZooKeeper data; no public exploit code or CISA KEV listing was identified at time of analysis, and vendor-released fixes exist in 3.9.6 and 3.8.7.

Affected VersionsENISA

Apache ZooKeeper 3.8.0 ≤3.8.6

Apache ZooKeeper 3.9.0 ≤3.9.5

Affected Packages

euvd apache_zookeeper no fix

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (CNA) PRIMARY 5.3 MEDIUM

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

Primary rating from Vendor (CNA) · only source for this CVE.

CVSS VectorVendor

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

None

Lifecycle Timeline

CVSS changed

Sep 17, 2026 - 20:22 NVD

5.3 (MEDIUM)

CVE Published

Sep 15, 2026 - 18:26 oss-security

HIGH

Description PRE-NVD

Disclosed via oss-security. NVD scoring and full description are pending.

Threat Intelligence Overview

EPSS Score

0.3%

Top 83% exploitable

Data Quality

4 sources

Confidence: Medium

EUVD 🇯🇵JVN

NVD

CVE.org

EPSS

VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity MEDIUM

CISA KEV No

Public POC No

EPSS 0.3%

Patch available No

Active threat No

Deciding rule

MEDIUM severity (CVSS 4.0-6.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Scheduled

Exploitation· derived

None

System Exposure· derived

Open

Automatable· derived

Yes

Human Impact· derived

Medium

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +26

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Code Injection CRITICAL

Code injection occurs when an application accepts user input and passes it directly into a language interpreter or evaluator without proper sanitization.