Command Injection Affecting pdfkit package, versions <0.8.7.2


0.0
critical

Snyk CVSS

    Attack Complexity Low
    Confidentiality High
    Integrity High
    Availability High

    Threat Intelligence

    Exploit Maturity Mature
    EPSS 28.06% (97th percentile)
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NVD
9.8 critical

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  • Snyk ID SNYK-RUBY-PDFKIT-2869795
  • published 8 Sep 2022
  • disclosed 14 Jun 2022
  • credit Benoit Côté-Jodoin

How to fix?

Upgrade pdfkit to version 0.8.7.2 or higher.

Overview

Affected versions of this package are vulnerable to Command Injection where the URL is not properly sanitized.

NOTE: This issue was originally addressed in 0.8.7, but the fix was not complete. A complete fix was released in 0.8.7.2.

PoC:

An application could be vulnerable if it tries to render a URL that contains query string parameters with user input:

PDFKit.new("http://example.com/?name=#{params[:name]}").to_pdf

If the provided parameter happens to contain a URL encoded character and a shell command substitution string, it will be included in the command that PDFKit executes to render the PDF:

irb(main):060:0> puts PDFKit.new("http://example.com/?name=#{'%20`sleep 5`'}").command
wkhtmltopdf --quiet [...] "http://example.com/?name=%20`sleep 5`" -
=> nil

Calling to_pdf on the instance shows that the sleep command is indeed executing:

PDFKit.new("http://example.com/?name=#{'%20`sleep 5`'}").to_pdf
# 5 seconds wait...

Of course, if the user can control completely the first argument of the PDFKit constructor, they can also exploit the command injection as long as it starts with "http":

PDFKit.new("http%20`sleep 5`").to_pdf