Arbitrary File Write via Archive Extraction (Zip Slip) Affecting sharpcompress Open this link in a new tab package, versions [,0.21.1)
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31 May 2018
17 Apr 2018
Snyk Security research Team
sharpcompress is a compression library for .NET Standard 1.0 that can unrar, decompress 7zip, decompress xz, zip/unzip, tar/untar lzip/unlzip, bzip2/unbzip2 and gzip/ungzip with forward-only reading and file random access APIs.
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
+2018-04-15 22:04:29 ..... 19 19 good.txt
+2018-04-15 22:04:42 ..... 20 20 ../../../../../../root/.ssh/authorized_keys
sharpcompress to version 0.21.1 or higher.