CVE-2021-37713 in node-tar
Summary
by MITRE • 08/31/2021
The npm package "tar" (aka node-tar) before versions 4.4.18, 5.0.10, and 6.1.9 has an arbitrary file creation/overwrite and arbitrary code execution vulnerability. node-tar aims to guarantee that any file whose location would be outside of the extraction target directory is not extracted. This is, in part, accomplished by sanitizing absolute paths of entries within the archive, skipping archive entries that contain `..` path portions, and resolving the sanitized paths against the extraction target directory. This logic was insufficient on Windows systems when extracting tar files that contained a path that was not an absolute path, but specified a drive letter different from the extraction target, such as `C:some\path`. If the drive letter does not match the extraction target, for example `D:\extraction\dir`, then the result of `path.resolve(extractionDirectory, entryPath)` would resolve against the current working directory on the `C:` drive, rather than the extraction target directory. Additionally, a `..` portion of the path could occur immediately after the drive letter, such as `C:../foo`, and was not properly sanitized by the logic that checked for `..` within the normalized and split portions of the path. This only affects users of `node-tar` on Windows systems. These issues were addressed in releases 4.4.18, 5.0.10 and 6.1.9. The v3 branch of node-tar has been deprecated and did not receive patches for these issues. If you are still using a v3 release we recommend you update to a more recent version of node-tar. There is no reasonable way to work around this issue without performing the same path normalization procedures that node-tar now does. Users are encouraged to upgrade to the latest patched versions of node-tar, rather than attempt to sanitize paths themselves.
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Analysis
by VulDB Data Team • 09/03/2021
The vulnerability CVE-2021-37713 affects the npm package "tar" also known as node-tar, which is widely used for handling tar archive files in node.js applications. This security flaw represents a critical path traversal issue that specifically impacts Windows operating systems where the tar extraction process fails to properly sanitize file paths. The vulnerability stems from inadequate path validation logic that was designed to prevent extraction of files outside the designated target directory but proved insufficient when dealing with Windows-specific path formats containing drive letters. The affected versions include 4.4.17 and earlier, 5.0.9 and earlier, and 6.1.8 and earlier releases of the node-tar package, making it a significant concern for developers who rely on this package for archive handling operations.
The technical flaw manifests when extracting tar archives on Windows systems where archive entries contain paths that specify a different drive letter than the extraction target directory. For instance, if the extraction target is located at D:\extraction\dir but an archive entry contains a path like C:some\path, the path resolution logic incorrectly resolves against the current working directory on the C: drive rather than the intended extraction target directory. This behavior creates a path traversal condition that allows malicious actors to write files to arbitrary locations on the system. Additionally, the vulnerability occurs when path components contain .. sequences immediately following a drive letter such as C:../foo, which the existing sanitization logic failed to properly detect and handle. This particular weakness in path normalization represents a classic security flaw that aligns with CWE-22 Path Traversal and CWE-73 Relative Path Traversal categories.
The operational impact of this vulnerability is severe as it enables both arbitrary file creation and arbitrary code execution capabilities. Attackers can exploit this flaw to overwrite critical system files, inject malicious code into the extraction target directory, or create files in locations where they should not have write permissions. The vulnerability specifically targets Windows environments where the path resolution behavior differs from Unix-like systems, making it particularly dangerous for applications that process untrusted tar archives from external sources. This issue affects not only local file system operations but also applications that rely on node-tar for deployment processes, package installation, or any scenario involving archive extraction from potentially malicious sources. The attack surface is expanded by the fact that this vulnerability can be exploited through legitimate use of the tar package, making it difficult to detect and prevent through traditional input validation approaches.
The remediation strategy involves upgrading to patched versions of node-tar where the path sanitization logic has been enhanced to properly handle Windows drive letter scenarios. Versions 4.4.18, 5.0.10, and 6.1.9 contain the necessary fixes that properly resolve paths against the extraction target directory regardless of drive letter specifications and correctly sanitize .. sequences that appear immediately after drive letters. The security advisory specifically notes that the v3 branch of node-tar has been deprecated and did not receive patches for these issues, emphasizing the importance of migrating to supported versions. Organizations should prioritize updating their node-tar dependencies and implement automated dependency monitoring to prevent similar vulnerabilities from affecting their applications. The advisory explicitly states that there is no reasonable workaround for this issue without implementing the same path normalization procedures that the patched versions now perform, making direct upgrade the only viable solution. This vulnerability also aligns with ATT&CK technique T1059 Command and Scripting Interpreter and T1203 Exploitation for Client Execution, as it enables attackers to execute arbitrary code through compromised archive extraction processes.