SharpZipLib (or #ziplib) is a Zip, GZip, Tar and BZip2 library. Starting version 1.0.0 and prior to version 1.3.3, a check was added if the destination file is under a destination directory. However, it is not enforced that _baseDirectory ends with slash. If the _baseDirectory is not slash terminated like /home/user/dir it is possible to create a file with a name thats begins as the destination directory one level up from the directory, i.e. /home/user/dir.sh. Because of the file name and destination directory constraints, the arbitrary file creation impact is limited and depends on the use case. Version 1.3.3 fixed this vulnerability.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-32842
• https://github.com/icsharpcode/SharpZipLib/releases/tag/v1.3.3
• https://securitylab.github.com/advisories/GHSL-2021-125-sharpziplib/