CVE-2026-84501
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.
How to fix
- apache zookeeper3.8.7, 3.9.6 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| apache zookeeper | 3.8.0 ≤ v < 3.8.7, 3.9.0 ≤ v < 3.9.6 | 3.8.7, 3.9.6 |
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