Critical Vulnerabilities in Fluent Bit Expose Cloud Environments to Remote Attacks
Fluent Bit, a widely adopted open-source logging and telemetry agent, has recently been found to contain a series of critical vulnerabilities that could allow attackers to remotely compromise cloud environments. With over 15 billion deployments globally, Fluent Bit plays a pivotal role in modern cloud infrastructures, including platforms like AWS, Microsoft Azure, and Kubernetes. The discovery of these flaws underscores the potential for widespread disruption and unauthorized access within these systems.
Overview of the Vulnerabilities
Security researchers have identified five critical vulnerabilities within Fluent Bit:
1. CVE-2025-12972: This vulnerability resides in the `out_file` plugin, where improper sanitization of tag values allows attackers to perform path traversal. By injecting sequences like ../ into tags, malicious actors can write files outside the intended directory, potentially leading to remote code execution (RCE) if the service runs with elevated privileges.
2. CVE-2025-12970: Found in the `in_docker` plugin, this flaw involves a stack buffer overflow due to inadequate validation of container names. Attackers controlling container names can exploit this to crash the service or execute arbitrary code.
3. CVE-2025-12978: This issue affects the `in_http`, `in_splunk`, and `in_elasticsearch` input plugins. A flaw in tag_key validation logic allows crafted inputs where a tag prefix is incorrectly treated as a full match. This can enable attackers to manipulate tags and redirect records to unintended destinations, compromising the authenticity of ingested logs.
4. CVE-2025-12977: Similar to CVE-2025-12978, this vulnerability in the same input plugins fails to sanitize `tag_key` inputs. Attackers can supply values containing special characters, leading to newline injection, path traversal, or log misrouting, thereby impacting data integrity and log routing.
5. CVE-2025-12969: Located in the `in_forward` plugin, this flaw arises from improper enforcement of the `security.users` authentication mechanism under certain configurations. Remote attackers can send unauthenticated data, injecting forged log records or manipulating routing decisions, which compromises the authenticity and integrity of ingested logs.
Technical Breakdown of Path Traversal and File Write Vulnerabilities
Among these, CVE-2025-12972 is particularly concerning. The `out_file` plugin writes logs directly to the filesystem using configuration parameters like `Path` and `File`. In configurations where only the `Path` is specified, filenames are derived from record tags. Due to insufficient sanitization, attackers can inject path traversal sequences into tags, enabling them to write files outside the intended directory. This can lead to the creation of malicious configuration files or executables in critical system locations, especially if Fluent Bit operates with elevated privileges, resulting in potential remote code execution.
Impact on Cloud Infrastructure
Fluent Bit’s integration into various cloud services means these vulnerabilities have far-reaching implications. Major cloud providers like AWS, Google Cloud, and Microsoft Azure embed Fluent Bit in their offerings. Exploitation of these flaws could disrupt cloud services, allow unauthorized data manipulation, and enable attackers to execute malicious code while concealing their activities. By controlling logging service behavior, adversaries can inject fake telemetry, reroute logs to unauthorized destinations, and alter event recordings.
Mitigation and Recommendations
The maintainers of Fluent Bit have addressed these vulnerabilities in version 4.1.0 and later. Users are strongly advised to upgrade to the latest version to mitigate these risks. For those unable to upgrade immediately, the following steps are recommended:
– Disable Affected Plugins: If the vulnerable plugins are not essential, consider disabling them to reduce the attack surface.
– Restrict Access: Limit network access to Fluent Bit instances, ensuring that only authorized users and services can interact with them.
– Implement Input Validation: Ensure that all inputs, especially those derived from external sources, are properly validated and sanitized to prevent injection attacks.
– Monitor Logs: Regularly review logs for unusual activities that might indicate exploitation attempts.
Conclusion
The discovery of these critical vulnerabilities in Fluent Bit highlights the importance of continuous security assessments in widely used open-source tools. Given Fluent Bit’s extensive deployment across cloud infrastructures, addressing these flaws promptly is crucial to maintaining the security and integrity of cloud environments.
