Thomas Wouters

An issue exists in the `tarfile` module when extracting untrusted tar archives. When using the `TarFile.extractall()` or `TarFile.extract()` functions with the `filter` parameter set to `data` or `tar`, it is possible to modify file metadata (such as last modified time) or file permissions (chmod) for files located outside the intended extraction directory. In Python 3.14 and later, the default value of the `filter` parameter changed to `data`, making users who rely on this default behavior susceptible to the issue. This can lead to arbitrary file modification on the system and potential data loss.

An issue in the `tarfile` module allows the extraction filter to be ignored when extracting untrusted tar archives. This can enable an attacker to create symbolic links that point outside the destination directory, modify file metadata, and potentially modify files in arbitrary filesystem locations, leading to data loss or unauthorized access to protected information. The issue occurs when using the `TarFile.extractall()` or `TarFile.extract()` functions with the `filter` parameter set to `data` or `tar`. For Python versions 3.14 and later, the default value of the `filter` parameter is `data`, making usage relying on this default behavior also susceptible.

The issue allows the extraction filter to be ignored, enabling symlink targets to point outside the destination directory and the modification of some file metadata. This affects users who utilize the tarfile module to extract untrusted tar archives using TarFile.extractall() or TarFile.extract() with the filter parameter set to "data" or "tar". For Python 3.14 and later, the default filter value changed to "data", which also affects usage relying on this new default behavior. The installation of source distributions, which are tar archives, is not significantly affected as they already allow arbitrary code execution during the build process.

Python incorrectly handles tar archive extraction when using the filtering option. Specifically, when `TarFile.errorlevel` is set to `0` during extraction with a filter, the system fails to skip filtered members as documented, extracting them instead. This issue could allow a remote attacker to modify files in arbitrary filesystem locations, potentially leading to data loss or compromising the integrity of protected information.

An issue in the `tarfile` module allows arbitrary filesystem writes outside the extraction directory when extracting untrusted tar archives. This occurs when using the `TarFile.extractall()` or `TarFile.extract()` functions with the `filter` parameter set to `data` or `tar`. For Python 3.14 and later, the default value of `filter` changed to `data`, making usage relying on this default behavior also susceptible. An attacker could exploit this to modify files in arbitrary locations, cause data loss, or potentially achieve privilege escalation or container escape if the scripts are executed with root privileges.