Arbitrary File Write via Archive Extraction (Zip Slip)

Overview

org.zeroturnaround:zt-zip is a library that helps to create, modify or extract ZIP archives.

Affected versions of the package are vulnerable to Arbitrary File Write via Archive Extraction (AKA "Zip Slip").

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

Vulnerable Method

This vulnerability appears in method process under class name Unpacker in org/zeroturnaround/zip/ZipUtil.java [1]

Remediation

Upgrade org.zeroturnaround:zt-zip to version 1.13 or higher.

References

• GitHub Commit
• Zip Slip Advisory
• Zip Slip Advisory