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Medium 5.4Published Nov 24, 2025

CVE-2025-12978CVE-2025-12978

Updated under an hour ago ()

Does this affect you?

It affects FluentBit Fluent Bit and 1 other product. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

Fluent Bit in_http, in_splunk, and in_elasticsearch input plugins contain a flaw in the tag_key validation logic that fails to enforce exact key-length matching. This allows crafted inputs where a tag prefix is incorrectly treated as a full match. A remote attacker with authenticated or exposed access to these input endpoints can exploit this behavior to manipulate tags and redirect records to unintended destinations. This compromises the authenticity of ingested logs and can allow injection of forged data, alert flooding and routing manipulation.

CVSS
5.4 MEDIUM (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L
Weakness (CWE)
CWE-187
Known exploited
Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days)
Not loaded for this CVE
Assigned by
certcc
NVD analysis
Analyzed
Record last updated
Jan 7, 2026
First seen by InfoSec Signals
Oct 9, 2026

Affected products

Affected products
FluentBit Fluent Bit
fluentbit:fluent_bit (from the name)
before 4.0.12
CNA record
treasuredata fluent_bit
treasuredata:fluent_bit
4.1.0
NVD

References

References

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.

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