Researchers at Tenable have identified a severe memory corruption vulnerability in Fluent Bit, an open-source logging utility integral to major cloud services. With over 3 billion downloads as of 2022 and an additional 10 million deployments daily, Fluent Bit is a cornerstone of cloud infrastructure used by prominent organisations such as VMware, Cisco, Adobe, Walmart, LinkedIn, and cloud giants like AWS, Microsoft, and Google Cloud.
The issue, dubbed "Linguistic Lumberjack" by Tenable, stems from how Fluent Bit's embedded HTTP server handles trace requests. The vulnerability can be exploited to cause denial of service (DoS), data leaks, or even remote code execution (RCE) in cloud environments.
"While vulnerabilities in major cloud providers like Azure, AWS, and GCP grab headlines, it's crucial to scrutinise the underlying technologies these services rely on," says Jimi Sebree, senior staff research engineer at Tenable. "Critical components like Fluent Bit, which are embedded in many cloud services, pose significant risks if compromised."
Tenable's researchers stumbled upon this flaw while investigating another security issue in a cloud service. They discovered they could access various internal metrics and logging endpoints of the cloud service provider, which included Fluent Bit instances. This cross-tenant data leakage revealed a more profound problem.
The vulnerability lies in the /api/v1/traces endpoint of Fluent Bit's monitoring API. The service fails to validate data types properly, allowing attackers to input non-string values that cause memory corruption. By manipulating these inputs, attackers can crash the service and leak sensitive data. Although exploiting this for RCE would require sophisticated, targeted efforts, the potential for harm remains high.
The bug affects Fluent Bit versions 2.0.7 through 3.0.3 and is tracked under CVE-2024-4323, with critical CVSS scores exceeding 9.5 out of 10. After reporting the issue on April 30, Fluent Bit's developers promptly addressed it by validating input data types in the problematic endpoint. The fix was implemented in the project's main branch on GitHub by May 15.
Organisations using Fluent Bit are strongly advised to update their software to the latest version immediately. Alternatively, administrators should review and restrict access to Fluent Bit's monitoring API to authorised users only, or disable it entirely if feasible.
The discovery of this vulnerability accentuates the importance of scrutinising not just the cloud services themselves but also the foundational technologies they depend on. Ensuring the security of tools like Fluent Bit is vital for maintaining the integrity of cloud environments across industries.
