CVE-2021-33645 in libtar
Summary
by MITRE • 08/11/2022
The th_read() function doesn’t free a variable t->th_buf.gnu_longlink after allocating memory, which may cause a memory leak.
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Analysis
by VulDB Data Team • 01/04/2026
The vulnerability identified as CVE-2021-33645 resides within the th_read() function of an archive handling library, specifically affecting the GNU tar implementation. This memory management flaw represents a classic memory leak scenario where allocated memory resources are not properly released, creating persistent resource consumption issues that can degrade system performance over time. The vulnerability manifests when the function processes archive entries and fails to free the t->th_buf.gnu_longlink variable after allocation, resulting in memory that remains allocated but unreferenced throughout the program execution lifecycle. Such memory leaks can accumulate particularly in long-running processes or applications that repeatedly process archive files, leading to progressive memory exhaustion that may eventually cause system instability or application crashes.
The technical nature of this vulnerability aligns with CWE-401, which specifically addresses memory leaks in software systems. This classification indicates that the flaw stems from improper memory management practices where allocated memory blocks are not properly deallocated, creating dangling references that consume system resources without providing any benefit to the application's operational functionality. The issue occurs during the processing of archive metadata, particularly when handling long link names that exceed standard limits and require extended storage mechanisms. The function's failure to properly manage this specific memory allocation creates a persistent resource drain that can compound under high load conditions or extended usage scenarios.
From an operational perspective, this vulnerability presents significant risks in environments where archive processing occurs frequently or in automated workflows. The memory leak can lead to gradual system performance degradation, potentially causing denial of service conditions where legitimate users experience reduced system responsiveness or complete service unavailability. Attackers could potentially exploit this vulnerability in resource exhaustion attacks, where repeated exploitation of the memory leak could force system instability or cause applications to crash, particularly in constrained environments such as embedded systems or containers with limited memory resources. The vulnerability is particularly concerning in server environments where tar operations are common and continuous processing occurs.
Mitigation strategies for CVE-2021-33645 should prioritize immediate code-level fixes that ensure proper memory management practices are implemented. Developers must modify the th_read() function to include explicit memory deallocation for the t->th_buf.gnu_longlink variable after its use, implementing proper resource cleanup routines that follow standard memory management protocols. System administrators should apply patches or updates from trusted sources that address this specific memory leak issue, particularly in environments where tar operations are frequent or automated. Regular monitoring of system memory usage and performance metrics can help detect potential exploitation of this vulnerability, while implementing process isolation and resource limits can provide additional protection against memory exhaustion scenarios. The remediation process should also include thorough code reviews to identify similar memory management issues within the same codebase, ensuring comprehensive vulnerability elimination across the entire software ecosystem.