---
cve: "CVE-2026-84501"
severity: "MEDIUM"
cvss: 5.3
epss: "0.8%"
vendor: "Apache Software Foundation"
kev: false
exploited: false
published: "2026-09-16 10:16:53"
tags: [cve, security, medium]
source: tsecurity.de CVE-Dossier
exported: "2026-09-21T23:11:14+02:00"
---

# CVE-2026-84501

> 5.3 MEDIUM

## Beschreibung

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-Vektor

```
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |
| S Scope | Unverändert | good |
| C Vertraulichkeit | Keine | good |
| I Integrität | Gering | warn |
| A Verfügbarkeit | Keine | good |

## Patch verfügbar (OSV)

- 9085db92dd679e1e90a63bfe6ae6345ab6cbc4ae (Commit)
- a355171b081b5b60749db8f19cca1528b0df936f (Commit)

## Referenzen

- <https://lists.apache.org/thread/ohby1g6zjt72p0w79rhbr41nczzvr33y>
- <http://www.openwall.com/lists/oss-security/2026/09/15/7>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-84501) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_