CVE-2021-38511 in tar Crate
Summary
by MITRE • 08/11/2021
An issue was discovered in the tar crate before 0.4.36 for Rust. When symlinks are present in a TAR archive, extraction can create arbitrary directories via .. traversal.
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Analysis
by VulDB Data Team • 08/15/2021
The vulnerability identified as CVE-2021-38511 resides within the tar crate version 0.4.35 and earlier in the Rust programming ecosystem, representing a critical directory traversal flaw that enables maliciously crafted tar archives to compromise system integrity. This issue specifically manifests when processing symbolic links within tar archives, creating a path traversal condition that allows attackers to write files outside of the intended extraction directory. The vulnerability stems from inadequate validation of symbolic link targets during archive extraction processes, permitting attackers to manipulate the extraction behavior through carefully constructed symlink entries that reference parent directory paths using the .. notation.
The technical implementation of this vulnerability exploits the fundamental trust placed in archive metadata during extraction operations. When a tar archive contains symbolic links that point to paths containing .. components, the extraction logic fails to properly sanitize these references, allowing the system to interpret these relative paths as legitimate targets for file creation. This flaw operates at the file system level where the tar crate's extraction routine processes symbolic links without adequate boundary checking, effectively bypassing normal directory restrictions and permissions. The vulnerability can be categorized under CWE-22 - Improper Limitation of a Pathname to a Restricted Directory, which specifically addresses path traversal issues in software systems.
Operationally, this vulnerability presents significant security implications for any system that processes untrusted tar archives, particularly in automated build systems, container image processing, and software distribution platforms. Attackers can leverage this flaw to create arbitrary directories and files in locations outside the intended extraction target, potentially leading to privilege escalation, data corruption, or system compromise. The impact extends beyond simple file creation to include potential denial of service scenarios where critical system directories become corrupted or filled with malicious content. This vulnerability particularly affects continuous integration systems, package managers, and any infrastructure that automatically extracts tar archives from untrusted sources, making it a widespread concern across software supply chain security.
Mitigation strategies for CVE-2021-38511 involve immediate upgrading to tar crate version 0.4.36 or later, which implements proper path validation and sanitization for symbolic link targets during extraction. Organizations should also implement additional protective measures including restricting extraction permissions, validating archive contents before processing, and employing sandboxed environments for archive handling. The remediation aligns with ATT&CK technique T1059.007 - Command and Scripting Interpreter: PowerShell, where attackers might exploit such vulnerabilities to establish persistence or escalate privileges. System administrators should also consider implementing network-level controls to prevent untrusted archive processing and establish comprehensive monitoring for suspicious file creation patterns that could indicate exploitation attempts. Regular security audits of dependency management systems are essential to ensure all components remain updated against known vulnerabilities.