VulnerabilityPublished 24 Nov 2025Updated 7 Jan 2026

CVE-2025-12978: FluentBit Fluent Bit · Partial String Comparison

Affects FluentBit Fluent BitSource CVE Database V5

Not known to be exploited · CVSS 5.4 Medium.

Data as of 26 Oct 2026, 11:42 UTC

CVSS 3.1 base score

5.4Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.4% chance of exploitation in 30 days – higher than 34% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: Low
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 24 Nov 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
FluentBit Fluent Bit	Affected =0	Fixed in–

AI-suggested

To mitigate this vulnerability, European organizations should: 1) Immediately review and restrict access to Fluent Bit input endpoints (in_http, in_splunk, in_elasticsearch) by implementing strong authentication and network segmentation to limit exposure. 2) Monitor and audit log routing configurations to detect unusual tag manipulations or unexpected log destinations. 3) Apply strict input validation and filtering rules where possible to prevent malformed tag inputs. 5) Employ anomaly detection on logging and alerting systems to identify alert flooding or suspicious log injection patterns. 6) Conduct regular security assessments of logging infrastructure to ensure no unauthorized access paths exist. 7) Consider deploying additional logging integrity verification mechanisms, such as cryptographic signing or checksums, to detect tampering. These steps go beyond generic advice by focusing on access control, monitoring, and proactive detection tailored to the nature of this vulnerability.

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.

Impact

For European organizations, the impact of this vulnerability can be significant, especially for those relying on Fluent Bit for centralized logging and monitoring in critical infrastructure, cloud services, and enterprise environments. Manipulated logs can lead to incorrect security alerts, masking of malicious activities, or injection of false data that could mislead incident response teams. Alert flooding can overwhelm monitoring systems, reducing their effectiveness. Misrouting logs to unintended destinations may result in data leakage or loss of audit trails, affecting compliance with regulations such as GDPR. The integrity and availability of logging data are crucial for forensic investigations and operational monitoring, so exploitation could degrade security posture and operational reliability. Organizations with exposed or weakly authenticated Fluent Bit input endpoints are at higher risk. The medium severity rating suggests that while the vulnerability is not trivial, it requires some level of access, limiting widespread exploitation but still posing a notable threat to targeted environments.

CWE-187Partial String Comparison (opens in a new tab)
Variant weakness
The product performs a comparison that only examines a portion of a factor before determining whether there is a match, such as a substring, leading to resultant weaknesses.
Testing
Thoroughly test the comparison scheme before deploying code into production. Perform positive testing as well as negative testing.
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

fluentbit.io/announcements/v4.1.0/ (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 7 Jan 2026, 19:45 UTC

WeaknessesCWE-187

Technical details

References

Community reviews

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