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Overview

unzipper is a library for the Uzip cross-platform streaming AP.I

Affected versions of this package are vulnerable to Arbitrary File Write via Archive Extraction (Zip Slip) in the extraction path validation in lib/extract.js and lib/Open/directory.js, which check only that the resolved path begins with the destination string (extractPath.indexOf(opts.path) != 0) without enforcing a directory-separator boundary. An attacker can write files outside the intended extraction directory, enabling file overwrite or code execution, by supplying a ZIP archive whose entry resolves to a sibling path such as /tmp/dest-evil/escaped.txt that shares the destination's string prefix, which a victim then extracts. Exploitation requires the victim to extract an untrusted archive with unzipper, and it works through sibling-prefix paths since standard ../../ traversal remains blocked.

Note: This is a bypass of the fix for the vulnerability described in CVE-2018-1002203.

Details

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

Remediation

There is no fixed version for unzipper.

References

• GitHub Advisory
• GitHub Issue