5.4

CVE-2025-12978: fluentbit fluent bit

CVSS: 5.4v3.1MediumAnalyzed
Published 24-11-2025Last modified 07-01-2026
Open JSON

Vulnerability summary

CVE-2025-12978 is a medium (CVSS 5.4) vulnerability in fluentbit fluent bit. EPSS estimates a 0.39% chance of exploitation in the next 30 days, higher than 32% of scored vulnerabilities.

Overall risk
22/100
0100
Low · default modelHow is this calculated?
CVSS score
5.4/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.39%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Timeline

  1. 24-11-2025
    PublishedVulnerability first disclosed.
  2. 07-01-2026
    Last modifiedVulnerability information updated.

Description

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 metrics

2 scores · 2 sources · 1 version

EPSS trend

Probability

0.39%

Chance of exploitation in the next 30 days

Percentile

32%

Versus all other CVEs

30-day change

0.00 pp

From 0.39% on 20-09-2026

20-09-202620-10-2026
EPSS score
0.39%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

No weakness data has been published for this record.

Affected systems

Fluentbit1 product
Treasuredata1 product

2 vendors · 2 products

References

1 links