Arbitrary File Write via Archive Extraction (Zip Slip) Affecting mqtt package, versions <0.7.0

mqtt is a Pure Ruby gem that implements the MQTT protocol, a lightweight protocol for publish/subscribe messaging.

Affected versions of this package are vulnerable to Arbitrary File Write via Archive Extraction (Zip Slip) due to the lack of hostname validation in the connection process. An attacker can intercept or manipulate data in transit by performing a man-in-the-middle attack.

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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