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Back to active CVEs
Medium · CVSS 5.3CVE-2026-84501

Apache ZooKeeper: Operational log forgery via newline injection in EnsembleAuthenticationProviderCVE-2026-84501

Answer in brief

CVE-2026-84501 records a Medium severity (CVSS 5.3) 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), Apache Software Foundation/org.apache.zookeeper: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 18, 2026Source checked Oct 31, 2026First seen by HOL Sep 16, 2026Material review Sep 18, 2026
Upstream Advisory

Key facts

Risk
Medium · CVSS 5.3
Exploitation
Not marked as known exploited
Affected software
3 mapped packages or products
Fix availability
Not reported

Why this deserves its current priority

CVSS is 5.3. 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), Apache Software Foundation/org.apache.zookeeper:zookeeper (generic). Check affected ranges and fixed versions before updating.

Affected products and reported versions
ProductAffected versionsFixed versions
cpe:2.3:a:apache:zookeeper:*:*:*:*:*:*:*:*Not reportedNot reported
Mapped affected packages and fixed versions
PackageAffected rangeFixed version
Apache Software Foundation/Apache ZooKeepergeneric3.9.0 || 3.8.0Not reported
Apache Software Foundation/org.apache.zookeeper:zookeepergeneric>=3.9.0 <=3.9.5 || >=3.8.0 <=3.8.6Not reported

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for Apache Software Foundation/Apache ZooKeeper, Apache Software Foundation/org.apache.zookeeper:zookeeper.
  2. 2Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

  1. Published upstream

    Sep 16, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Sep 18, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Sep 16, 2026

Sources and claim methodology

  • Source referencelists.apache.org
  • Source referenceopenwall.com
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.

Record context

Vulnerability class
Missing Auth
EPSS
Not reported
CWE IDs
CWE-117
Source
CVE List V5
Source checked
Oct 31, 2026
References
2 linked sources
Open source record