CVE-2021-47417 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
libbpf: Fix memory leak in strset
Free struct strset itself, not just its internal parts.
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Analysis
by VulDB Data Team • 08/22/2025
The vulnerability identified as CVE-2021-47417 resides within the Linux kernel's libbpf library, specifically addressing a memory management issue in the strset data structure implementation. This flaw represents a classic memory leak scenario that can accumulate over time and potentially lead to system resource exhaustion. The libbpf library serves as a foundational component for eBPF (extended Berkeley Packet Filter) programs, which are widely used for network filtering, system monitoring, and performance analysis within the Linux ecosystem. The vulnerability manifests when the strset structure fails to properly release all allocated memory resources during cleanup operations.
The technical flaw occurs in the memory deallocation routine where the strset structure itself is not being freed, despite properly releasing its internal components. This type of memory leak falls under the category of improper resource management and can be categorized as CWE-404, which specifically addresses "Improper Resource Management" in software development practices. The root cause lies in the incomplete cleanup implementation where developers only addressed the memory allocated for the internal elements of strset but neglected to free the structure's own memory footprint. This oversight creates a persistent memory leak that grows with each usage of the affected functionality, particularly impacting systems that frequently employ eBPF programs for monitoring or filtering tasks.
The operational impact of this vulnerability extends beyond simple memory consumption issues, as it can lead to progressive system degradation and potential denial of service conditions. Systems running numerous eBPF programs or those that frequently create and destroy strset structures will experience increasing memory pressure, potentially leading to out-of-memory conditions that could affect system stability and performance. The vulnerability is particularly concerning in high-throughput environments such as network monitoring appliances, security appliances, or systems running extensive eBPF-based security tools. Attackers could potentially exploit this memory leak to cause system instability or perform resource exhaustion attacks, though direct exploitation for privilege escalation or remote code execution is not typically associated with memory leaks of this nature.
Mitigation strategies for CVE-2021-47417 primarily involve updating the Linux kernel to versions that include the patched libbpf implementation. System administrators should prioritize applying security patches from their respective kernel vendors, as the fix requires kernel-level modifications that cannot be addressed through user-space applications alone. The remediation process should include thorough testing of eBPF-based applications and monitoring for any unexpected behavior following the patch application. Organizations should also implement memory monitoring tools to detect unusual memory consumption patterns that might indicate the presence of similar memory management issues in their systems. Additionally, the vulnerability highlights the importance of comprehensive code review processes for memory management functions and adherence to security best practices such as those outlined in the ATT&CK framework's system security concepts, which emphasize proper resource handling and memory management as fundamental defensive measures against system instability and potential exploitation vectors.