Critical Flaws in Fluent Bit Expose Cloud Infrastructure

Fluent Bit, a ubiquitous log-processing tool integral to modern cloud infrastructure, is facing a significant security challenge. Recent analysis has uncovered five critical vulnerabilities within its framework. These flaws could potentially enable attackers to bypass authentication, write arbitrary files, and even achieve full agent takeover.

The implications of these vulnerabilities are far-reaching, given Fluent Bit’s widespread deployment. It operates across various environments, including containers, Kubernetes DaemonSets, and major cloud platforms. Such critical weaknesses in a foundational tool could have cascading effects throughout the cloud ecosystem.

Unveiling Critical Flaws in a Core Cloud Component

Oligo Security, in a collaborative disclosure with Amazon Web Services, revealed the profound security risks associated with Fluent Bit. The identified vulnerabilities pose a threat of complete compromise to cloud infrastructure, highlighting the tool’s critical role and the severity of these findings. This revelation underscores the need for immediate action and heightened vigilance in cloud security practices.

Uri Katz, a researcher at Oligo Security’s CTO Office, emphasized the pervasive nature of Fluent Bit in a recent blog post. He noted its presence in diverse sectors, including AI laboratories, financial institutions, automotive manufacturers, and all leading cloud providers such as AWS, Google Cloud, and Microsoft Azure. According to Katz, the failure of such a widely trusted and deployed component does not merely expose individual systems but endangers the overall stability of the cloud ecosystem.

The disclosed vulnerabilities could empower malicious actors to manipulate critical data. Potential attack scenarios include rewriting or deleting logs to obscure illicit activities, injecting fabricated telemetry data, or rerouting record streams to attacker-controlled destinations. More alarmingly, these flaws could facilitate the execution of arbitrary code, granting attackers deep control over compromised systems.

In response to these critical findings, the Fluent Bit project has promptly released patched versions. Users are strongly advised to upgrade to v4.1.1 or v4.0.12 to mitigate the identified risks. This swift action is crucial for maintaining the integrity and security of cloud environments relying on Fluent Bit.

Authentication Bypass and Log Manipulation Risks

One of the most alarming vulnerabilities uncovered involves the Fluent Bit forward input plugin, specifically “in_forward.” This plugin, despite being configurable with “Security.Users” authentication, can remain effectively unprotected if a “Shared.key” is not simultaneously specified. This oversight leaves a critical port open, allowing unauthorized attackers to connect and transmit arbitrary logs without proper verification.

Attackers exploiting this flaw could unleash a torrent of false or misleading events into monitoring systems. Such an influx could be used to obscure legitimate alerts within a deluge of noise, making it difficult for security teams to identify actual threats. Furthermore, malicious actors could hijack the entire telemetry stream, gaining control over vital system insights. This critical issue has been formally tracked as CVE-2025-12969, and its severity valuation is currently pending. The potential for widespread data corruption and operational disruption makes this a high-priority concern for cloud security.

Additional vulnerabilities center on the “tag” mechanism, which is fundamental to how Fluent Bit routes and processes logs. One significant bug, identified as CVE-2025-12978, allows an attacker to impersonate trusted tags by merely guessing the first character of the tag key. This seemingly minor flaw could enable the rerouting of logs or the bypass of established security filters, leading to unauthorized data movement. Another flaw, CVE-2025-12977, involves unsanitized tag values, which can be exploited to inject harmful characters. These injections, including newlines, directory-traversal strings, and control characters, can corrupt downstream parsing processes. This corruption could potentially enable file-system writes or facilitate further privilege escalation within a compromised system.

AWS has affirmed that it has taken measures to secure its internal systems that rely on Fluent Bit, implementing the necessary updates provided by the Fluent Bit project. The company has also released Fluent Bit version 4.1.1, ensuring its customers benefit from the latest security patches. This proactive approach by a major cloud provider highlights the importance of addressing these vulnerabilities expeditiously to safeguard cloud operations and customer data.

Remote Code Execution and System Takeover Potential

Beyond authentication and log manipulation, Oligo’s research also brought to light a critical chain of vulnerabilities that could lead to remote code execution and path traversal attacks affecting Fluent Bit. One such vulnerability, CVE-2025-12972, targets the “out_file” output plugin. This specific flaw becomes critical when Tag values are under user control and a fixed File parameter is not explicitly set. Under these conditions, attackers can maliciously craft Tag values, such as using “../”, to perform path-traversal file writes or overwrites. This capability could allow them to plant malicious files on the system or, more severely, achieve remote code execution, granting unauthorized control over the Fluent Bit agent and potentially the underlying system.

Uri Katz noted the long-standing nature of some of these vulnerabilities, stating that certain flaws, including CVE-2025-12972, have potentially left cloud environments exposed for over eight years. This extended period of vulnerability underscores the latent risks in widely deployed open-source tools and the ongoing necessity for thorough security audits and continuous patching. The discovery of such long-standing vulnerabilities highlights the importance of consistent security evaluations across the software supply chain.

Another critical vulnerability, CVE-2025-12970, affects the Docker input plugin, specifically “in-Docker,” and manifests as a stack buffer overflow. If an attacker manages to name a container with an excessively long string, this action can trigger the buffer overflow. The immediate consequences could range from crashing the Fluent Bit agent, causing disruptions in log collection, to enabling the execution of arbitrary code. Oligo’s warnings emphasize that a successful exploitation of this flaw could allow attackers to seize control of the logging agent entirely. Such a takeover would enable them to hide their malicious activities, plant backdoors for persistent access, and pivot further into the compromised system, escalating the attack from log manipulation to full system compromise.

Fluent Bit holds a prestigious position as a Cloud Native Computing Foundation (CNCF) graduated open-source project. Initially conceived by Eduardo Silva, who remains its most prolific contributor, the project now benefits from the sponsorship and maintenance of major cloud providers. This collective support underscores its critical role in the cloud-native ecosystem. The collaborative effort to identify and patch these vulnerabilities reflects the shared responsibility within the open-source community and cloud providers to maintain robust security for essential infrastructure components. Ensuring the ongoing security of such fundamental tools is paramount for the integrity of global cloud operations.