CVE-2023-30620

An unsafe extraction is being performed using tarfile.extractall() from a remotely retrieved tarball. Which may lead to the writing of the extracted files to an unintended location. Sometimes, the vulnerability is called a TarSlip or a ZipSlip variant.

Details

I commented the following snippet of code as a vulnerability details. The code is from file.py#L26..L134

@ns_conf.route('/<name>')
@ns_conf.param('name', "MindsDB's name for file")
class File(Resource):
    @ns_conf.doc('put_file')
    def put(self, name: str):
        ''' add new file
            params in FormData:
                - file
                - original_file_name [optional]
        '''

        data = {}

        ... omitted for brevity

            url = data['source']
            data['file'] = data['name']

            ... omitted for brevity 

            with requests.get(url, stream=True) as r:                   # Source: retrieve the URL which point to a remotely located tarball 
                if r.status_code != 200:
                    return http_error(
                        400,
                        "Error getting file",
                        f"Got status code: {r.status_code}"
                    )
                file_path = os.path.join(temp_dir_path, data['file'])
                with open(file_path, 'wb') as f:
                    for chunk in r.iter_content(chunk_size=8192):   # write with chunks the remote retrieved file into file_path location 
                        f.write(chunk)

        original_file_name = data.get('original_file_name')

        file_path = os.path.join(temp_dir_path, data['file'])      
        lp = file_path.lower()
        if lp.endswith(('.zip', '.tar.gz')):
            if lp.endswith('.zip'):
                with zipfile.ZipFile(file_path) as f:
                    f.extractall(temp_dir_path)
            elif lp.endswith('.tar.gz'):
                with tarfile.open(file_path) as f:  # Just after 
                    f.extractall(temp_dir_path)  # Sink: the tarball located by file_path is supposed to be extracted to temp_dir_path. 

So, a remotely available tarball is being retrieved and written to the server filesystem in chunks, and then, if the extension ends with .tar.gz of a compressed tarball, the mindsdb app applies tarfile.extractall() directly with no checks for the destination.

However, according to the following warning from the official documentation;

Warning: Never extract archives from untrusted sources without prior inspection. It is possible that files are created outside of path, e.g. members that have absolute filenames starting with "/" or filenames with two dots "..".

PoC

The following PoC is provided for illustration purposes only. It showcases the risk of extracting a non-harmless text file sim4n6.txt to one of the parent locations rather than the intended current folder.

> tar --list -v -f archive.tar.gz
tar: Removing leading "../../../" from member names
../../../sim4n6.txt

> python3 
Python 3.10.6 (main, Nov  2 2022, 18:53:38) [GCC 11.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import tarfile
>>> with tarfile.open("archive.tar.gz") as tf:
>>>         tf.extractall()
>>> exit()

> test -f ../../../sim4n6.txt && echo "sim4n6.txt exists"
sim4n6.txt exists

Attack Scenario

An attacker could craft a malicious tarball with a filename path, such as ../../../../../../../../etc/passwd, and then serve the archive remotely, proceed to the PUT request of the tarball through mindsdb and overwrite the system files of the hosting server for instance.

Mitigation

Potential mitigation could be to:

• Use a safer module, like zipfile.
• Use an alternative of tarfile, such as tarsafe.
• Validate the location or the absolute path of the extracted files and discard those with malicious paths such as relative path ../../.. or absolute path such as /etc/password. A simple wrapper could be written to raise an exception when a path traversal may be identified.

This is similar to the other report GHSA-7x45-phmr-9wqp.