Arbitrary File Write via Archive Extraction (Zip Slip) Affecting github.com/rclone/rclone/cmd/rcd package, versions <1.49.4
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11 Oct 2019
11 Sep 2019
Semmle Security Research
How to fix?
github.com/rclone/rclone/cmd/rcd to version 1.49.4 or higher.
github.com/rclone/rclone/cmd/rcd is a package part of rclone - "rsync for cloud storage".
Affected versions of this package are vulnerable to Arbitrary File Write via Archive Extraction (Zip Slip). Files within a zip file can break out of the target directory when being extracted.
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
+2018-04-15 22:04:29 ..... 19 19 good.txt
+2018-04-15 22:04:42 ..... 20 20 ../../../../../../root/.ssh/authorized_keys