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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Apache Software Foundation | Apache ZooKeeper | 3.9.0 – ≤ 3.9.5, 3.8.0 – ≤ 3.8.6 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | zookeeper | 3.9.6-1 | — |
| Debian 13 | zookeeper | No fix yet | — |
| Debian 12 | zookeeper | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | zookeeper | No fix yet | — |
| Ubuntu 26.04 LTS | zookeeper | No fix yet | — |
| Ubuntu 24.04 LTS | zookeeper | No fix yet | — |
| Ubuntu 22.04 LTS | zookeeper | No fix yet | — |
| Ubuntu 20.04 LTS | zookeeper | No fix yet | — |
Show 3 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 18.04 LTS | zookeeper | No fix yet | — |
| Ubuntu Pro 16.04 LTS | zookeeper | No fix yet | — |
| Ubuntu Pro 14.04 LTS | zookeeper | No fix yet | — |
Advisories 2
- WID-SEC-2026-3908 IBM SPSS: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 3, 2026
- WID-SEC-2026-4089 Oracle Construction and Engineering: Mehrere Schwachstellen BSI CERT-Bund (WID) · Oct 20, 2026
References
- https://lists.apache.org/thread/ohby1g6zjt72p0w79rhbr41nczzvr33y vendor-advisory