Overview
A critical security vulnerability, identified as CVE-2025-12969, has been discovered in the in_forward input plugin of Fluent Bit. This vulnerability allows remote attackers with network access to the Fluent Bit instance to send unauthenticated data, potentially leading to severe consequences. This bypass occurs due to improper enforcement of the security.users authentication mechanism under specific, vulnerable configuration settings.
Technical Details
The vulnerability stems from an inadequate validation process within the in_forward plugin. Under certain configuration circumstances, the authentication mechanism defined by security.users can be circumvented. This allows attackers to bypass intended security controls and inject arbitrary data directly into the Fluent Bit pipeline. Exploitation requires network access to the port where the Fluent Bit in_forward plugin is listening.
CVSS Analysis
At the time of writing, a CVSS score for CVE-2025-12969 is not yet available (N/A). However, given the potential for unauthenticated data injection and the impact on log integrity, it is anticipated that the assigned CVSS score will be rated as HIGH to CRITICAL once finalized. We will update this article as soon as a CVSS score is published.
Severity: N/A
CVSS Score: N/A
Possible Impact
Successful exploitation of CVE-2025-12969 can have significant security implications, including:
- Forged Log Records: Attackers can inject malicious or misleading log entries, potentially obscuring malicious activity or framing legitimate users.
- Alerting System Flooding: The injection of fabricated logs can trigger false alarms, overwhelming security personnel and masking genuine security incidents.
- Routing Manipulation: Attackers might manipulate routing decisions within the Fluent Bit pipeline, directing sensitive data to unauthorized locations.
- Compromised Log Integrity and Authenticity: The overall reliability and trustworthiness of the ingested logs are significantly compromised, hindering accurate security analysis and incident response.
Mitigation and Patch Steps
The recommended course of action is to upgrade to Fluent Bit version 4.1.0 or later. This version contains a fix that properly enforces the security.users authentication mechanism.
To mitigate the risk before upgrading, carefully review your Fluent Bit configuration for the in_forward input plugin. Ensure that the security.users option is correctly configured and that network access to the Fluent Bit instance is restricted to trusted sources only. Consider using network segmentation and firewall rules to limit exposure.
Upgrade Instructions:
- Refer to the official Fluent Bit documentation for detailed upgrade instructions relevant to your specific deployment environment.
- Thoroughly test the upgraded Fluent Bit instance in a non-production environment before deploying to production.
- Verify that the
security.usersauthentication mechanism is functioning correctly after the upgrade.
