Arbitrary File Write via Archive Extraction (Zip Slip)

Affecting sharpcompress package, versions [,0.21.1)

Overview

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 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

Remediation

Upgrade sharpcompress to version 0.21.1 or higher.

References

Do your applications use this vulnerable package?

CVSS Score

5.5
medium severity
  • Attack Vector
    Local
  • Attack Complexity
    Low
  • Privileges Required
    None
  • User Interaction
    Required
  • Scope
    Unchanged
  • Confidentiality
    None
  • Integrity
    High
  • Availability
    None
CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
Credit
Snyk Security research Team
CVE
CVE-2018-1002206
CWE
CWE-29
Snyk ID
SNYK-DOTNET-SHARPCOMPRESS-60246
Disclosed
17 Apr, 2018
Published
31 May, 2018