archivers/ark: fix vulnerability in tar extraction

KDE Project Security Advisory

Title: Ark: maliciously crafted TAR archive with symlinks can install files outside the extraction directory.
Risk Rating: Important
CVE: CVE-2020-24654
Versions: ark <= 20.08.0
Author: Elvis Angelaccio <elvis.angelaccio@kde.org>
Date: 27 August 2020

Overview

A maliciously crafted TAR archive containing symlink entries
would install files anywhere in the user's home directory upon extraction.

Proof of concept

For testing, an example of malicious archive can be found at
https://github.com/jwilk/traversal-archives/releases/download/0/dirsymlink.tar

Impact

Users can unwillingly install files like a modified .bashrc, or a malicious
script placed in ~/.config/autostart.

Workaround

Before extracting a downloaded archive using the Ark GUI, users should inspect it
to make sure it doesn't contain symlink entries pointing outside the extraction folder.

The 'Extract' context menu from the Dolphin file manager shouldn't be used.

Solution

Ark 20.08.1 skips maliciously crafted symlinks when extracting TAR archives.

Alternatively, https://invent.kde.org/utilities/ark/-/commit/8bf8c5ef07b0ac5e914d752681e470dea403a5bd can be applied to previous
releases.

Credits

Thanks to Fabian Vogt for reporting this issue and for fixing it.

MFH: 2020Q3
Security: CVE-2020-24654