Vulnerability 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.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Apache | Zookeeper | >= 3.8.0, < 3.8.7 |
Related Weaknesses (CWE)
References
- https://lists.apache.org/thread/ohby1g6zjt72p0w79rhbr41nczzvr33yMailing ListVendor Advisory
- http://www.openwall.com/lists/oss-security/2026/09/15/7Mailing List
FAQ
What is CVE-2026-84501?
CVE-2026-84501 is a vulnerability with a CVSS score of 5.3 (MEDIUM). 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 ...
How severe is CVE-2026-84501?
CVE-2026-84501 has been rated MEDIUM with a CVSS base score of 5.3/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-84501?
Check the references section above for vendor advisories and patch information. Affected products include: Apache Zookeeper.