All the vulnerabilities related to the version 3.2.3 of the package
Arbitrary File Overwrite in tar
Versions of tar prior to 4.4.2 for 4.x and 2.2.2 for 2.x are vulnerable to Arbitrary File Overwrite. Extracting tarballs containing a hardlink to a file that already exists in the system, and a file that matches the hardlink will overwrite the system's file with the contents of the extracted file.
For tar 4.x, upgrade to version 4.4.2 or later. For tar 2.x, upgrade to version 2.2.2 or later.
Arbitrary File Creation/Overwrite via insufficient symlink protection due to directory cache poisoning using symbolic links
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, where the symlink and directory names in the archive entry used backslashes as a path separator on posix systems. The cache checking logic used both \ and / characters as path separators, however \ is a valid filename character on posix systems.
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.
Additionally, a similar confusion could arise on case-insensitive filesystems. If a tar archive contained a directory at FOO, followed by a symbolic link named foo, then on case-insensitive file systems, the creation of the symbolic link would remove the directory from the filesystem, but not from the internal directory cache, as it would not be treated as a cache hit. A subsequent file entry within the FOO directory would then be placed in the target of the symbolic link, thinking that the directory had already been created.
These issues were addressed in releases 4.4.16, 5.0.8 and 6.1.7.
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. If this is not possible, a workaround is available below.
4.4.16 || 5.0.8 || 6.1.7
Users may work around this vulnerability without upgrading by creating a custom filter method which prevents the extraction of symbolic links.
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 patched versions, rather than attempt to sanitize tar input themselves.
The problem is addressed in the following ways:
/ as a path separator, replacing \ with / on Windows systems, and leaving \ intact in the path on posix systems. This is performed in depth, at every level of the program where paths are consumed.Note that this means that the entry objects exposed in various parts of tar's API will now always use / as a path separator, even on Windows systems. This is not expected to cause problems, as / is a valid path separator on Windows systems, but may result in issues if entry.path is compared against a path string coming from some other API such as fs.realpath() or path.resolve().
Users are encouraged to always normalize paths using a well-tested method such as path.resolve() before comparing paths to one another.
Arbitrary File Creation/Overwrite on Windows via insufficient relative path sanitization
Arbitrary File Creation, Arbitrary File Overwrite, Arbitrary Code Execution
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.
4.4.18 || 5.0.10 || 6.1.9
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.
The fixed versions strip path roots from all paths prior to being resolved against the extraction target folder, even if such paths are not "absolute".
Additionally, a path starting with a drive letter and then two dots, like c:../, would bypass the check for .. path portions. This is checked properly in the patched versions.
Finally, a defense in depth check is added, such that if the entry.absolute is outside of the extraction taret, and we are not in preservePaths:true mode, a warning is raised on that entry, and it is skipped. Currently, it is believed that this check is redundant, but it did catch some oversights in development.
Arbitrary File Creation/Overwrite via insufficient symlink protection due to directory cache poisoning using symbolic links
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 two directories and a symlink with names containing unicode values that normalized to the same value. Additionally, on Windows systems, long path portions would resolve to the same file system entities as their 8.3 "short path" counterparts. A specially crafted tar archive could thus include directories with two forms of the path that resolve to the same file system entity, followed by a symbolic link with a name in the first form, lastly followed by a file using the second form. It led to bypassing 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.
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. If this is not possible, a workaround is available below.
6.1.9 || 5.0.10 || 4.4.18
Users may work around this vulnerability without upgrading by creating a custom filter method which prevents the extraction of symbolic links.
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 patched versions, rather than attempt to sanitize tar input themselves.
The problem is addressed in the following ways, when comparing paths in the directory cache and path reservation systems:
String.normalize('NFKD') method is used to first normalize all unicode to its maximally compatible and multi-code-point form./ on Windows systems (on posix systems, \ is a valid filename character, and thus left intact).Denial of service while parsing a tar file due to lack of folders count validation
During some analysis today on npm's node-tar package I came across the folder creation process, Basicly if you provide node-tar with a path like this ./a/b/c/foo.txt it would create every folder and sub-folder here a, b and c until it reaches the last folder to create foo.txt, In-this case I noticed that there's no validation at all on the amount of folders being created, that said we're actually able to CPU and memory consume the system running node-tar and even crash the nodejs client within few seconds of running it using a path with too many sub-folders inside
You can reproduce this issue by downloading the tar file I provided in the resources and using node-tar to extract it, you should get the same behavior as the video
Here's a video show-casing the exploit:
Denial of service by crashing the nodejs client when attempting to parse a tar archive, make it run out of heap memory and consuming server CPU and memory resources
This report was originally reported to GitHub bug bounty program, they asked me to report it to you a month ago