Vulnerability in Apache Software Foundation Apache ZooKeeper

[ Description ]Official 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.

[ Fixes ]Fixes and patches

No fix or interim patch is linked from our sources yet. Check the vendor references below and limit exposure of affected systems until a fix is available.

[ Advisories ]Government CERT advisories

• BSI CERT-Bund20 Oct 2026WID-SEC-2026-4089

  Oracle Construction and Engineering: Multiple vulnerabilities Translated from German

  Risk highCVE-2026-101736CVE-2026-91399CVE-2026-49844+9 more CVEs
• BSI CERT-Bund13 Oct 2026WID-SEC-2026-3908

  IBM SPSS: Multiple vulnerabilities Translated from German

  CVE-2026-59969CVE-2026-84501CVE-2026-79993+2 more CVEs

[ References ]References

• lists.apache.org/thread/ohby1g6zjt72p0w79rhbr41nczzvr33yvendor-advisory