Arbitrary File Write via Archive Extraction (Zip Slip) Affecting elfinder.netcore package, versions [0,]



    Exploit Maturity Mature
    Attack Complexity Low
    Confidentiality High
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9.8 critical

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  • published 20 Aug 2021
  • disclosed 20 Aug 2021
  • credit Timo Müller

How to fix?

There is no fixed version for elFinder.NetCore.


elFinder.NetCore is a file manager for Web.

Affected versions of this package are vulnerable to Arbitrary File Write via Archive Extraction (Zip Slip). The ExtractAsync function within the FileSystem is vulnerable to arbitrary extraction due to insufficient validation.


* Upload the genearted to the server
* extract the file in elfinder
* You now should fine a file in the /tmp/ directory


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