CVE-2025-12978
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedFluent 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceFluent Bit's in_http, in_splunk, and in_elasticsearch input plugins have a flaw in tag_key validation that fails to enforce exact key-length matching. This causes tag prefixes to be incorrectly treated as complete matches, allowing remote attackers with endpoint access to manipulate tags and redirect log records to unintended destinations.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data= 4.1.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- Low
- Availability
- Low
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify Fluent Bit versionRun `fluent-bit --version` or `fluent-bit -V` to retrieve the installed version numberAffected if The installed version is exactly 4.1.0 of Treasuredata Fluent Bit
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Check if in_http plugin is configured with tag_keyExamine the Fluent Bit configuration file for an input section using the in_http plugin with a tag_key parameter setAffected if The in_http input plugin is enabled and tag_key is configured
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Check if in_splunk plugin is configured with tag_keyExamine the Fluent Bit configuration file for an input section using the in_splunk plugin with a tag_key parameter setAffected if The in_splunk input plugin is enabled and tag_key is configured
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Check if in_elasticsearch plugin is configured with tag_keyExamine the Fluent Bit configuration file for an input section using the in_elasticsearch plugin with a tag_key parameter setAffected if The in_elasticsearch input plugin is enabled and tag_key is configured
A user is affected if they are running Treasuredata Fluent Bit version 4.1.0 AND have any of the three input plugins (in_http, in_splunk, or in_elasticsearch) configured with a tag_key setting.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataImplement exact key-length matching in tag_key validation logic across all three affected plugins; restrict network access to input endpoints and enforce strong authentication.
- Consultation3.0 h
- Implementation6.0 h
- Testing5.0 h
- Review / QA3.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,752.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2025-12978 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-12978 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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