Affected versions of this package are vulnerable to Directory Traversal via TarFile.extractall() and TarFile.extract() functions in the tarfile module when using the filter parameter set to data or tar. An attacker can gain unauthorised access to files outside the intended extraction directory and modify file metadata by crafting malicious tar archives that exploit the extraction filter bypass.

Note:

Users of Python 3.14 or later should be aware that the default value of filter= changed from no filtering to data, so if you are relying on this new default behaviour then your usage is also affected.

For the users that are unable to upgrade to the fixed version it is recommended to mitigate this issue by rejecting links inside tarfiles that use relative references to the parent directory. The upstream advisory provides this example code:

# Avoid insecure segments in link names.
for member in tar.getmembers():
    if not member.islnk():
        continue
    if os.pardir in os.path.split(member.linkname):
        raise OSError("Tarfile with insecure segment ('..') in linkname")

Now safe to extract members with the data filter.
tar.extractall(filter="data")

A Directory Traversal attack (also known as path traversal) aims to access files and directories that are stored outside the intended folder. By manipulating files with "dot-dot-slash (../)" sequences and its variations, or by using absolute file paths, it may be possible to access arbitrary files and directories stored on file system, including application source code, configuration, and other critical system files.

Directory Traversal vulnerabilities can be generally divided into two types:

• Information Disclosure: Allows the attacker to gain information about the folder structure or read the contents of sensitive files on the system.

st is a module for serving static files on web pages, and contains a vulnerability of this type. In our example, we will serve files from the public route.

If an attacker requests the following URL from our server, it will in turn leak the sensitive private key of the root user.

curl http://localhost:8080/public/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/root/.ssh/id_rsa

Note %2e is the URL encoded version of . (dot).

• Writing arbitrary files: Allows the attacker to create or replace existing files. This type of vulnerability is also known as Zip-Slip.

One way to achieve this is by using a malicious zip archive that holds path traversal filenames. When each filename in the zip archive gets concatenated to the target extraction folder, without validation, the final path ends up outside of the target folder. If an executable or a configuration file is overwritten with a file containing malicious code, the problem can turn into an arbitrary code execution issue quite easily.

The following is an example of a zip archive with one benign file and one malicious file. Extracting the malicious file will result in traversing out of the target folder, ending up in /root/.ssh/ overwriting the authorized_keys file:

2018-04-15 22:04:29 .....           19           19  good.txt
2018-04-15 22:04:42 .....           20           20  ../../../../../../root/.ssh/authorized_keys

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