Critical Bug Discovery in Fluent Bit
Cybersecurity researchers have discovered a set of critical vulnerabilities affecting Fluent Bit, a widely used telemetry agent with more than 15 billion deployments. These flaws highlight weaknesses in essential components that organizations use to move logs, metrics and traces across banking, cloud and software-as-a-service (SaaS) platforms.
According to an advisory from Oligo Security, the flexibility of Fluent Bit can become a significant risk if data sanitization fails. The problems identified lie in input handling, label processing and output management.
Types of Identified Vulnerabilities
The security flaws cover a range of issues, from incorrect input validation to buffer overflows. Researchers have noted that these problems, already serious individually, become even more dangerous when combined.
The main vulnerabilities include:
- Input validation and tag processing: An attacker with network access could forge tags to redirect logs or inject malicious logs. This could poison data sets or feed false signals to security tools.
- Path Traversal Bugs: These flaws allow attackers to manipulate file paths. The main risk is the overwriting of sensitive files on the affected system.
- Stack Buffer Overflow: A stack buffer overflow was encountered during Docker metrics analysis. This type of vulnerability can threaten system stability or, in more serious cases, allow remote code execution.
- Authentication Bypass: A flaw was identified in the forward input plugin that leaves some relays exposed to anyone who can access the port.
Patched Versions and Security Recommendations
The Fluent Bit vulnerabilities have been addressed in versions v4.1.1 and v4.0.12, both released in early October 2025. Previous versions of Fluent Bit remain vulnerable to these attacks.
To mitigate exposure, Fluent Bit traders must take immediate steps:
- Update: Install the latest stable versions (v4.1.1 or v4.0.12).
- Avoid dynamic labels: Discourage the use of dynamic labels in routing.
- Restrict output parameters: Lock output file parameters to limit manipulation.
- Least Privilege Principle: Run Fluent Bit with least privilege access.
- Read-only configuration directories: Mount configuration directories as read-only.
Impact on the Cloud Ecosystem
Fluent Bit plays a crucial role in Kubernetes environments and cloud log management. An incorrect configuration or an unpatched system could distort visibility into critical operations across financial services, delivery applications, security products, and SaaS environments.
Oligo Security emphasizes that rapid patching is essential to protect the integrity of the observability pipelines that support critical business operations. Although the disclosure process took longer than expected due to gaps in open source vulnerability classification, AWS quickly collaborated in coordinating fixes.