CVE-2021-32803: Arbitrary File Creation/Overwrite via insufficient symlink protection due to directory cache poisoning
Impact
Arbitrary File Creation, Arbitrary File Overwrite, Arbitrary Code Execution
node-tar aims to guarantee that any file whose location would be modified by a symbolic link is not extracted. This is, in part, achieved by ensuring that extracted directories are not symlinks. Additionally, in order to prevent unnecessary stat calls to determine whether a given path is a directory, paths are cached when directories are created.
This logic was insufficient when extracting tar files that contained both a directory and a symlink with the same name as the directory. This order of operations resulted in the directory being created and added to the node-tar directory cache. When a directory is present in the directory cache, subsequent calls to mkdir for that directory are skipped. However, this is also where node-tar checks for symlinks occur.
By first creating a directory, and then replacing that directory with a symlink, it was thus possible to bypass node-tar symlink checks on directories, essentially allowing an untrusted tar file to symlink into an arbitrary location and subsequently extracting arbitrary files into that location, thus allowing arbitrary file creation and overwrite.
This issue was addressed in releases 3.2.3, 4.4.15, 5.0.7 and 6.1.2.
Patches
3.2.3 || 4.4.15 || 5.0.7 || 6.1.2
Workarounds
Users may work around this vulnerability without upgrading by creating a custom filter method which prevents the extraction of symbolic links.
js const tar = require('tar')
tar.x({ file: 'archive.tgz', filter: (file, entry) => { if (entry.type === 'SymbolicLink') { return false } else { return true } } })
Users are encouraged to upgrade to the latest patch versions, rather than attempt to sanitize tar input themselves.
Other sources
Node.js tar module could allow a local attacker to traverse directories on the system, caused by insufficient symlink protection. An attacker could use a specially-crafted tar file containing "dot dot" sequences (/../) to create or overwrite arbitrary files on the system.
— IBM
The npm package "tar" (aka node-tar) before versions 6.1.2, 5.0.7, 4.4.15, and 3.2.3 has an arbitrary File Creation/Overwrite vulnerability via insufficient symlink protection. node-tar aims to guarantee that any file whose location would be modified by a symbolic link is not extracted. This is, in part, achieved by ensuring that extracted directories are not symlinks. Additionally, in order to prevent unnecessary stat calls to determine whether a given path is a directory, paths are cached when directories are created. This logic was insufficient when extracting tar files that contained both a directory and a symlink with the same name as the directory. This order of operations resulted in the directory being created and added to the node-tar directory cache. When a directory is present in the directory cache, subsequent calls to mkdir for that directory are skipped. However, this is also where node-tar checks for symlinks occur. By first creating a directory, and then replacing that directory with a symlink, it was thus possible to bypass node-tar symlink checks on directories, essentially allowing an untrusted tar file to symlink into an arbitrary location and subsequently extracting arbitrary files into that location, thus allowing arbitrary file creation and overwrite. This issue was addressed in releases 3.2.3, 4.4.15, 5.0.7 and 6.1.2.
The npm package "tar" (aka node-tar) has an arbitrary File Creation/Overwrite vulnerability via insufficient symlink protection. node-tar aims to guarantee that any file whose location would be modified by a symbolic link is not extracted. This is, in part, achieved by ensuring that extracted directories are not symlinks. Additionally, in order to prevent unnecessary stat calls to determine whether a given path is a directory, paths are cached when directories are created.
Affected Software
Remediation
Patch Available
Event History
Parent advisories
This vulnerability appears in the following advisories.
Frequently Asked Questions
What is CVE-2021-32803?
CVE-2021-32803 is a vulnerability in the node-tar package that allows a local attacker to traverse directories on the system by exploiting insufficient symlink protection.
What is the severity of CVE-2021-32803?
The severity of CVE-2021-32803 is high with a CVSS score of 8.1.
How does CVE-2021-32803 affect the node-tar package?
CVE-2021-32803 affects the npm package "tar" (aka node-tar) versions before 6.1.2, 5.0.7, 4.4.15, and 3.2.3.
How can I fix CVE-2021-32803?
To fix CVE-2021-32803, you need to update the node-tar package to version 6.1.2, 5.0.7, 4.4.15, or 3.2.3.
Where can I find more information about CVE-2021-32803?
You can find more information about CVE-2021-32803 on the following references: npmjs.com, GitHub advisory GHSA-r628-mhmh-qjhw, and the GitHub commit 9dbdeb6df8e9dbd96fa9e84341b9d74734be6c20.