py7zr 0.20.0 Directory Traversal

Risk: Medium
Local: No
Remote: Yes

CVE-2022-44900: path traversal vulnerability in py7zr Directory traversal vulnerability in SevenZipFile.extractall() function of the python library py7zr version 0.20.0 and earlier allow attackers to read arbitrary files on the local machine via malicious 7z file extraction. CVE-2022-44900 <> vulnerability allows attackers to achieve arbitrary file read and arbitrary file write. To do so, an attacker needs to create a malicious 7z archive containing a symlink to achieve an arbitrary file read and a file with a path traversal payload as name to achieve an arbitrary file write. Exploiting The script used for tests is the following: import py7zr import click @click.command() @click.argument("filename") def main_procedure(filename): with py7zr.SevenZipFile(filename, 'r') as archive: archive.extractall() main_procedure() The vulnerabile function targeted is py7zr.SevenZipFile.extractall(). A lab setup has been built to test for vulnerabilities. Directories structured as follow were used: ├── start_point │ ├── archive.7z │ └── └── target ├── write └── read The start_point directory contains the script used for tests and the malicious archive containing the path traversal payload in the form of the filename of an archived file. To achieve an arbitrary file read, one of the files in the archives needs to have ../target/write set as name. The content of the file will be written into target/write. In a similar way, to achieve an arbitrary file read, a symlink pointing to ../target/read needs to be present in the archive. When extracted the symlink will consist of the content of target/read. Disclosure timeline 29/10/2022 - Maintainer was notified privately of the vulnerabilities 30/10/2022 - Response from maintainer 01/11/2022 - Release of patched version 0.20.1 01/11/2022 - CVE ID request 06/12/2022 - CVE ID obtained 06/12/2022 - Public disclosure ------------------------------

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