CVE-2025-12977VulnerabilityPublished 24 Nov 2025Updated 7 Jan 2026

CVE-2025-12977: FluentBit Fluent Bit · Partial String Comparison

Affects FluentBit Fluent BitSource CVE Database V5

Not known to be exploited · CVSS 9.1 Critical.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

9.1Critical

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

EPSS: 0.7% chance of exploitation in 30 days – higher than 54% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

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

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: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
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: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within 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 2026-10-25.

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 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

European organizations should immediately audit their Fluent Bit deployments to identify usage of the in_http, in_splunk, and in_elasticsearch input plugins. Until official patches are released, organizations should implement strict input validation and sanitization at the network perimeter or proxy level to block tag_key values containing newline characters, path traversal sequences, or other special characters. Restrict network access to Fluent Bit input endpoints to trusted sources only, employing network segmentation and firewall rules. Monitor logs for unusual tag_key values or routing anomalies that could indicate exploitation attempts. Consider temporarily disabling vulnerable input plugins if feasible or isolating Fluent Bit instances handling untrusted data. Engage with Fluent Bit maintainers and subscribe to security advisories for timely patch releases. Additionally, enhance monitoring and alerting on log integrity and routing failures to detect exploitation early.

Description

Fluent Bit in_http, in_splunk, and in_elasticsearch input plugins fail to sanitize tag_key inputs. An attacker with network access or the ability to write records into Splunk or Elasticsearch can supply tag_key values containing special characters such as newlines or ../ that are treated as valid tags. Because tags influence routing and some outputs derive filenames or contents from tags, this can allow newline injection, path traversal, forged record injection, or log misrouting, impacting data integrity and log routing.

Impact

For European organizations, the impact of CVE-2025-12977 can be severe, especially those relying on Fluent Bit for centralized logging, security monitoring, and compliance reporting. Exploitation could lead to unauthorized modification or injection of log data, undermining the integrity of security logs and audit trails critical for incident detection and forensic analysis. Path traversal could allow attackers to overwrite or access sensitive files on logging servers, potentially leading to data breaches or disruption of logging infrastructure. Misrouting of logs can cause loss of visibility into security events, delaying detection of other attacks. Industries with strict regulatory requirements such as finance, healthcare, and critical infrastructure in Europe could face compliance violations and reputational damage. The network-based attack vector and lack of required authentication make it easier for attackers to exploit this vulnerability remotely, increasing the risk to cloud environments and hybrid deployments common in European enterprises.

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).
CWE-1287Improper Validation of Specified Type of Input (opens in a new tab)
Base weakness
The product receives input that is expected to be of a certain type, but it does not validate or incorrectly validates that the input is actually of the expected type.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

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

WeaknessesCWE-187, CWE-1287

Technical details

References

Community reviews

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