CVE-2021-33646 in libtar
Summary
by MITRE • 08/11/2022
The th_read() function doesn’t free a variable t->th_buf.gnu_longname 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-2021-33646 represents a memory management flaw within the th_read() function of an archive handling library. This issue manifests as a memory leak where allocated memory for the t->th_buf.gnu_longname variable is not properly released after use, creating a persistent resource consumption problem that can accumulate over time.
The technical root cause stems from improper memory deallocation within the archive reading process. When the th_read() function processes archive entries, it allocates memory for the gnu_longname field to accommodate extended file path information required by the GNU tar format. However, the function fails to execute proper cleanup operations, leaving the allocated memory segment in an unreferenced state. This memory leak occurs specifically during the parsing of archive entries that utilize the GNU tar extended format features, where long file names exceed standard limits and require additional storage space.
The operational impact of this vulnerability extends beyond simple resource consumption concerns. While individual memory leaks may appear minor, they can compound over extended system operation, particularly in applications that continuously process large numbers of archive files or maintain long-running archive processing services. The cumulative effect can lead to gradual memory exhaustion, potentially causing application instability, performance degradation, or system resource starvation that affects overall system reliability and availability.
This vulnerability aligns with CWE-401, which specifically addresses improper deallocation of memory, and represents a classic example of resource management failure in archive processing software. The flaw demonstrates poor adherence to secure coding practices and memory management protocols that are fundamental to preventing resource exhaustion attacks and maintaining system stability.
Mitigation strategies should focus on implementing proper memory management within the th_read() function, ensuring that all allocated memory segments are properly freed after use. Security teams should conduct comprehensive code reviews to identify similar memory management issues across the codebase and implement automated memory leak detection tools during development and testing phases. Additionally, regular application monitoring should be established to detect unusual memory consumption patterns that may indicate the presence of such vulnerabilities.
The vulnerability also relates to ATT&CK technique T1499.001, which covers resource exhaustion attacks through memory consumption. While this specific vulnerability may not be directly exploitable for malicious purposes, it creates conditions that could be leveraged by attackers to perform resource exhaustion attacks, particularly in environments where archive processing services are exposed to untrusted input. Organizations should consider this vulnerability as part of their broader security posture assessment and implement appropriate defensive measures including input validation, resource limits, and monitoring for anomalous behavior patterns.
Security remediation requires immediate patching of the affected library and implementation of comprehensive memory management practices throughout the archive processing codebase. Regular security assessments should be conducted to identify similar memory management issues, and development teams should be trained on secure coding practices to prevent recurrence of such vulnerabilities in future implementations.