Operational log forgery via unsanitized ensemble name
Published Sep 16, 2026 · Updated Sep 16, 2026
Log injection in Apache ZooKeeper 3.8.0 through 3.8.6 and 3.9.0 through 3.9.5 allows remote attackers to forge operational log entries. EnsembleAuthenticationProvider.handleAuthentication() passes a mismatched ensemble name containing newline characters directly to a LOG.warn() SLF4J placeholder without neutralizing line breaks. Unauthenticated access to the client port is sufficient to insert entries with attacker-chosen timestamps, levels, class names, and messages that appear genuine.
Summary
What happened
Log injection in Apache ZooKeeper 3.8.0 through 3.8.6 and 3.9.0 through 3.9.5 allows remote attackers to forge operational log entries. EnsembleAuthenticationProvider.handleAuthentication() passes a mismatched ensemble name containing newline characters directly to a LOG.warn() SLF4J placeholder without neutralizing line breaks. Unauthenticated access to the client port is sufficient to insert entries with attacker-chosen timestamps, levels, class names, and messages that appear genuine.
The record
- CVE
- CVE-2026-84501
- Published
- Sep 16, 2026
- Updated
- Sep 16, 2026
- Vendor
- The Apache Software Foundation
- Product
- Apache ZooKeeper
- Classifications
- Unavailable
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 16, 2026CVE publishedPublication date reported by the CVE source.
- Sep 16, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=3.8.0 <=3.8.6
- Affected versionversion=3.9.0 <=3.9.5
What conditions does exploitation require?
What is affected?
Published CVSS scores
No CVSS assessment is available in this record.
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
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Public exploit references
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Technologies
Your stack
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Your stack
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