A set of critical vulnerabilities affecting Fluent Bit, a widely used telemetry agent deployed more than 15 billion times, has been uncovered by cybersecurity researchers.
The issues highlight weaknesses in components that organizations depend on to move logs, metrics and traces across banking, cloud and software-as-a-service (SaaS) platforms.
According to a new advisory published today by Oligo Security, a series of flaws in inputs, tag processing and output handling show that Fluent Bit’s flexibility can become a liability when sanitization fails.
These problems have been addressed in Fluent Bit v4.1.1 and v4.0.12, released in early October 2025. Older versions remain at risk.
Vulnerabilities identified span improper input validation, partial string comparisons and path traversal bugs. In several cases, attackers with network access could spoof tags, inject malicious records or manipulate file paths. Other issues include a stack buffer overflow in Docker metrics parsing and an authentication bypass in the forward input plugin.
Read more on Fluent Bit vulnerabilities: Critical Fluent Bit Bug Impacts All Major Cloud Platforms
Oligo warned that these flaws, individually serious, become even more dangerous when combined.
Manipulating tags can redirect logs, poison datasets or feed false signals into security tools. Path traversal could overwrite sensitive files, while the overflow bug could threaten system stability or enable code execution. The forward input bypass leaves some relays exposed to anyone who can reach the port.
Required Updates and Operator Guidance
Operators are being urged to take immediate steps to reduce exposure from the newly disclosed Fluent Bit vulnerabilities.
Recommendations include:
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Updating to the latest stable releases
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Avoiding dynamic tags in routing
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Locking down output file parameters
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Running Fluent Bit with least-privilege access
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Mounting configuration directories as read-only
The research team noted that disclosure took longer than expected due to gaps in open-source vulnerability triage. AWS, however, reportedly responded rapidly and collaborated on coordinated fixes.
Fluent Bit’s central role in Kubernetes and cloud logging means misconfigurations or unpatched systems could distort visibility across financial services, delivery apps, security products and SaaS environments.
Oligo warned that swift patching is essential to protect the integrity of observability pipelines that support critical operations.
