Apache ZooKeeper: Operational log forgery via newline injection in EnsembleAuthenticationProvider (CVE-2026-84501) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-84501

Apache ZooKeeper: Operational log forgery via newline injection in EnsembleAuthenticationProvider

Answer in brief

CVE-2026-84501 records a Unknown severity vulnerability in Apache ZooKeeper: Operational log forgery via newline injection in EnsembleAuthenticationProvider. The current sources do not mark it as known exploited. The current feed maps Apache Software Foundation/Apache ZooKeeper (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 16, 2026Updated Sep 16, 2026Source checked Sep 16, 2026First seen by HOL Sep 16, 2026Material review Sep 16, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Apache Software Foundation/Apache ZooKeeper (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Apache Software Foundation/Apache ZooKeepergeneric	3.9.0 \|\| 3.8.0	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Apache Software Foundation/Apache ZooKeeper.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Sep 16, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 16, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 16, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.