A severe memory corruption vulnerability has been discovered in Fluent Bit, a widely used cloud logging utility across major cloud platforms. This open-source tool collects, processes, and forwards logs and other application data. With over 3 billion downloads as of 2022 and an additional 10 million deployments each day, Fluent Bit is heavily utilized by major organizations such as VMware, Cisco, Adobe, Walmart, and LinkedIn, as well as nearly every major cloud service provider, including AWS, Microsoft, and Google Cloud.
The issue, dubbed “Linguistic Lumberjack,” arises from the way Fluent Bit’s embedded HTTP server parses trace requests. If exploited, it can cause denial of service (DoS), data leakage, or remote code execution (RCE) in a cloud environment.
Discovery and Impact
The vulnerability, tracked as CVE-2024-4323, was introduced in version 2.0.7 and persists through version 3.0.3. Tenable researchers discovered this flaw while investigating a separate security issue in an undisclosed cloud service. They realized they could access various internal metrics and logging endpoints of the cloud service provider (CSP), including instances of Fluent Bit. This cross-tenant data leakage revealed the broader issue within Fluent Bit’s monitoring API.
Fluent Bit’s API is designed to allow users to query and monitor internal data, such as service uptime, plugin metrics, and health checks. The /api/v1/traces endpoint, in particular, was found to be vulnerable to memory corruption when non-string values, like integers, were passed as input names. This could result in various issues, including crashes, heap overwrites, and information leaks.
Mitigations and Recommendations
The bug has been fixed in the main source branch on GitHub as of May 15, 2024, with the patch expected in the release of version 3.0.4. Organizations using Fluent Bit in their infrastructure are advised to update to the latest version as soon as possible. If upgrading is not feasible, it’s recommended to review configurations related to Fluent Bit’s monitoring API to ensure only authorized users and services can query it, or to disable the endpoint altogether if not in use.
Technical Details
Fluent Bit’s monitoring API endpoints allow administrators to query internal service information. The vulnerability in the /api/v1/traces endpoint occurs when data types of input names are not validated, assuming they are valid MSGPACK_OBJECT_STRs. Passing non-string values causes memory corruption issues, leading to crashes and data leaks. Specific integer values can cause various memory corruption issues, such as heap buffer overflows and stack corruption.
In testing, Tenable researchers could reliably exploit this vulnerability to crash the service and retrieve adjacent memory chunks, potentially leaking sensitive information. Although achieving RCE would require significant effort and customization to the target environment, the ease of causing DoS and information leaks makes this vulnerability particularly concerning.
Conclusion
Organizations relying on Fluent Bit, whether in their own infrastructure or via cloud services, should prioritize updating to the latest version to mitigate this critical vulnerability. Ensuring robust security measures, such as regular updates and limiting access to monitoring APIs, is essential to protect against potential exploitation.
How Can Netizen Help?
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