Researchers have identified a critical memory corruption vulnerability in Fluent Bit, a widely-used cloud logging utility. This open-source tool, essential for collecting, processing, and forwarding logs and other application data, has over 3 billion downloads as of 2022 and sees about 10 million new deployments daily. Major organizations such as VMware, Cisco, Adobe, Walmart, LinkedIn, and cloud giants like AWS, Microsoft, and Google Cloud rely on Fluent Bit.
The vulnerability, named “Linguistic Lumberjack” by Tenable, is rooted in how Fluent Bit’s embedded HTTP server handles trace requests. Exploiting this flaw can lead to denial of service (DoS), data leakage, or remote code execution (RCE) within cloud environments.
“People often focus on vulnerabilities in Azure, AWS, or GCP, but overlook the core technologies these services depend on. Vulnerabilities in common components like Fluent Bit affect all major cloud providers,” says Jimi Sebree, senior staff research engineer at Tenable. “We need to scrutinize application security at the component level, not just the service level.”
Discovery of the Vulnerability
Tenable researchers stumbled upon this vulnerability while investigating a separate security issue in an undisclosed cloud service. They unexpectedly accessed internal metrics and logging endpoints of the cloud service provider, including instances of Fluent Bit. This cross-tenant data leakage was traced back to endpoints in Fluent Bit’s monitoring API, designed for querying and monitoring internal data.
A particular endpoint, /api/v1/traces, failed to validate data types properly before parsing. By inputting non-string values, attackers could trigger memory corruption issues. Testing with various integer values caused service crashes and potential data leaks. This method could also enable attackers to achieve RCE, though it requires considerable effort tailored to the target’s operating system and architecture.
Mitigation Measures
The bug affects Fluent Bit versions 2.0.7 through 3.0.3 and is tracked under CVE-2024-4323, with CVSS scores exceeding 9.5, marking it as critical. Fluent Bit maintainers released a fix on May 15, following its report on April 30. The update ensures proper validation of data types in the problematic endpoint.
Organizations using Fluent Bit should update their installations immediately. Alternatively, administrators can configure Fluent Bit’s monitoring API to restrict access to authorized users and services or disable access entirely.
This vulnerability highlights the importance of securing the foundational technologies underpinning major cloud platforms, emphasizing the need for rigorous application security practices at every level.