Log redirection via partial tag key matching
Published Nov 24, 2025 · Updated Jan 7, 2026
Partial string comparison in Fluent Bit before 4.0.12 allows remote attackers to redirect records through crafted input. The in_http, in_splunk, and in_elasticsearch plugins accept a tag_key prefix as a full key instead of requiring equal key lengths. Access to an exposed or authenticated input endpoint is required; exploitation injects forged log data, floods alerts, or routes records to unintended destinations.
Summary
What happened
Partial string comparison in Fluent Bit before 4.0.12 allows remote attackers to redirect records through crafted input. The in_http, in_splunk, and in_elasticsearch plugins accept a tag_key prefix as a full key instead of requiring equal key lengths. Access to an exposed or authenticated input endpoint is required; exploitation injects forged log data, floods alerts, or routes records to unintended destinations.
The record
- CVE
- CVE-2025-12978
- Published
- Nov 24, 2025
- Updated
- Jan 7, 2026
- Vendor
- Fluent Bit
- Product
- Fluent Bit
- Classifications
- CWE-187, T1565.001
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Nov 24, 2025CVE publishedPublication date reported by the CVE source.
- Jan 7, 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?
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- Affected versionversion=0 <4.0.12
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
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Public exploit references
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Technologies
Your stack
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Your stack
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