FluentBit 4.1.0 out_file path traversal

Summaryinfo

A vulnerability was found in FluentBit 4.1.0. It has been rated as critical. Affected by this issue is the function out_file of the component out_file. The manipulation leads to path traversal. This vulnerability is traded as CVE-2025-12972. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability, which was classified as critical, has been found in FluentBit 4.1.0. This issue affects the function out_file of the component out_file. The manipulation with an unknown input leads to a path traversal vulnerability. Using CWE to declare the problem leads to CWE-35. The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize '.../...//' (doubled triple dot slash) sequences that can resolve to a location that is outside of that directory. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

Fluent Bit out_file plugin does not properly sanitize tag values when deriving output file names. When the File option is omitted, the plugin uses untrusted tag input to construct file paths. This allows attackers with network access to craft tags containing path traversal sequences that cause Fluent Bit to write files outside the intended output directory.

The advisory is shared at fluentbit.io. The identification of this vulnerability is CVE-2025-12972 since 11/10/2025. The exploitation is known to be easy. The attack may be initiated remotely. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 12/22/2025). MITRE ATT&CK project uses the attack technique T1006 for this issue.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2025-198810). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Productinfo

Name

• FluentBit

Version

• 4.1.0

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CPE 2.2info

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If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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