CVE-2026-84501
Apache ZooKeeper: Operational log forgery via newline injection in EnsembleAuthenticationProvider
- State
- Published
- Severity
- 5.3 Medium
- Published
- Sep 16, 2026
- Updated
- Sep 16, 2026
- Reserved
- Sep 1, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 5.3 Medium | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N | CISA-ADP |
Weaknesses
- CWE-117 Improper output neutralization for logs
Affected Products
| Product | Versions |
|---|---|
Apache ZooKeeperApache Software Foundation |
|
References
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