CVE-2026-84501
Received
Received - Intake
Log Injection in Apache ZooKeeper
Vulnerability report for CVE-2026-84501, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.
Publication date: 2026-09-16
Last updated on: 2026-09-16
Assigner: Apache Software Foundation
Description
Description
An unauthenticated attacker can inject arbitrary fake log lines into Apache ZooKeeper's operational log by sending a crafted add_auth("ensemble", ...) request containing newline characters (\n). When the ensemble name doesn't match, EnsembleAuthenticationProvider.handleAuthentication() logs the raw, unsanitized name via LOG.warn(). Because SLF4J's {} placeholder preserves embedded newlines, the attacker can forge complete log entries — with arbitrary timestamps, log levels, class names, and messages — that are visually indistinguishable from genuine ZooKeeper log output.
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 3.8.7 or 3.9.6, which fixes the issue.
CVSS Scores
EPSS Scores
| Probability: | |
| Percentile: |
Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| apache | zookeeper | From 3.8.0 (inc) to 3.8.6 (inc) |
| apache | zookeeper | From 3.9.0 (inc) to 3.9.5 (inc) |
| apache | zookeeper | 3.8.7 |
| apache | zookeeper | 3.9.6 |
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-117 | The product constructs a log message from external input, but it does not neutralize or incorrectly neutralizes special elements when the message is written to a log file. |
