Improper Output Neutralization for Logs Affecting zookeeper-3.9 package, versions <3.9.6-r0
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-MINIMOSLATEST-ZOOKEEPER39-19957976
- published20 Sept 2026
- disclosed16 Sept 2026
Introduced: 16 Sep 2026
NewCVE-2026-84501 (opens in a new tab)How to fix?
Upgrade Minimos:latest zookeeper-3.9 to version 3.9.6-r0 or higher.
NVD Description
Note: Versions mentioned in the description apply only to the upstream zookeeper-3.9 package and not the zookeeper-3.9 package as distributed by Minimos.
See How to fix? for Minimos:latest relevant fixed versions and status.
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.
References
- https://www.cve.org/CVERecord?id=CVE-2026-84501
- https://github.com/advisories/GHSA-mm24-r27q-hxg5
- https://osv.dev/vulnerability/MINI-m2rg-c72r-jgxp
- https://osv.dev/vulnerability/CVE-2026-84501
- https://lists.apache.org/thread/ohby1g6zjt72p0w79rhbr41nczzvr33y
- http://www.openwall.com/lists/oss-security/2026/09/15/7