Fluent Bit Security Vulnerabilities

Conducted research has brought to light five severe security issues within Fluent Bit, a widely deployed open‑source telemetry agent. When chained together, these weaknesses give threat actors multiple paths to seize control of cloud assets, interfere with log integrity, or disrupt service availability across cloud and Kubernetes environments.

How Attackers Could Exploit the Flaws

The uncovered defects collectively open the door to authentication bypass, file manipulation, remote code execution, service disruption, and tag tampering. If weaponized, they provide an intruder with the ability to corrupt logs, mask malicious activity, inject fabricated telemetry, and pivot deeper into cloud infrastructure.

Breakdown of the Identified CVEs

The following vulnerabilities illustrate how broad the attack surface becomes when Fluent Bit processes untrusted input:

• CVE‑2025‑12972 – A path traversal weakness tied to unsanitized tag values being used to generate filenames. This exposes systems to arbitrary file writes, log tampering, and potential code execution.
• CVE‑2025‑12970 – A stack buffer overflow in the Docker Metrics input plugin (in_docker). Crafting containers with overly long names could trigger a crash or result in remote code execution.
• CVE‑2025‑12978 – A logic flaw in tag matching that allows spoofed trusted tags by guessing only the initial character of a Tag_Key, enabling attackers to reroute logs, bypass filtering, and inject manipulated records.
• CVE‑2025‑12977 – Improper validation of tags derived from attacker‑controlled fields. Malicious input may inject traversal sequences, newlines, or control characters that corrupt downstream log pipelines.
• CVE‑2025‑12969 – Missing authentication in the in_forward plugin used by Fluent Bit instances communicating via the Forward protocol. This omission permits injection of forged logs or flooding of downstream security tools with fabricated events.

Potential Impact on Cloud Operations

Together, these vulnerabilities grant extensive influence over how Fluent Bit collects, processes, and stores telemetry data. A determined attacker may redirect or suppress essential events, plant misleading information, erase signs of intrusion, or trigger malicious code execution through manipulated logs. Given Fluent Bit’s wide adoption, these risks threaten the reliability of enterprise cloud environments and the trustworthiness of their logging infrastructure.

Patches and Vendor Guidance

The issues were resolved following coordinated disclosure, with fixes provided in Fluent Bit versions 4.1.1 and 4.0.12, released in October 2025. AWS, which also took part in the disclosure process, advises all customers using Fluent Bit to update promptly to remain protected.

Security Recommendations

To reduce exposure and strengthen monitoring pipelines, experts recommend tightening configuration and restricting attack surfaces. Key defensive actions include:

Avoid using dynamic tags for routing and restrict output paths to prevent tag‑driven path expansion or traversal.

Mount configuration directories such as /fluent-bit/etc/ as read‑only, block runtime manipulation, and run Fluent Bit under non‑root accounts.

Context From Earlier Discoveries

This disclosure follows a previous Fluent Bit vulnerability reported more than a year earlier: CVE‑2024‑4323, also known as Linguistic Lumberjack. That flaw affected the agent’s built‑in HTTP server and exposed instances to DoS conditions, data exposure, or remote code execution. The newly identified issues underscore the continuing importance of securing telemetry tools that form the foundation of cloud observability.