Arbitrary File Write via Archive Extraction (Zip Slip) Affecting baserproject/basercms package, versions <4.5.4

baserproject/basercms is a Content management system based on CakePHP.

Affected versions of this package are vulnerable to Arbitrary File Write via Archive Extraction (Zip Slip). In the admin panel of basercms, an administrator with privileges to perform maintenance operations, has access to the page /admin/tools/maintenance. This page has a functionality used to restore the database data by uploading a ZIP archive. An attacker could abuse this functionality to perform a ZIP slip attack by uploading a malicious ZIP archive.

This is due to invalid ZIP archive filename check via the _readFile method of the class Simplezip in the file lib/Baser/Vendor/Simplezip.php, and an attacker can a file with the following path: ../../../../../../../webroot/code.php. This would cause code.php to be saved in the webroot directory.

This vulnerability requires gaining specific admin privileges, i.e. - another vulnerability before this one to be exploited successfully.

It is exploited using a specially crafted zip archive, that holds path traversal filenames. When exploited, a filename in a malicious archive is concatenated to the target extraction directory, which results in the final path ending up outside of the target folder. For instance, a zip may hold a file with a "../../file.exe" location and thus break out 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 malicous 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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