CVE-2026-84501Medium· 5.3▾ SunlitAn 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, Ense…
▾ Sunlit zone — Low / medium · no exploitation signal
impact 29.2 · likelihood 0.2 · exploitation 0
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Stakeholder-Specific Vulnerability Categorization from CISA's ADP record at CVE.org: whether exploitation is observed, whether an attack can be automated, and how much of the system is at stake.
Exploit-prediction probability, daily snapshots since Sep 18.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
— → 5.3
none → medium
Last analysed / modified upstream
0.4%
0.4% → 0.8%
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.
zookeeper >= 3.8.0, < 3.8.7zookeeper >= 3.9.0, < 3.9.6Upgrade past the affected range:
zookeeper 3.9.6Field changes observed since this record was first indexed.
Connected by shared product, vendor, weakness, or advisory.
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