How to prevent the latest ImageMagick vulnerability?

Question

According to the CVE-2016–3714 there are a some vulnerabilities in the ImageMagick program (4 packages) :

Insufficient filtering for filename passed to delegate's command allows remote code execution during conversion of several file formats

There are others programs and command lines dependent on the imagemagick package, ( an example here). By executing the ImageMagick program, an image file can receive malicious code.

What are the recommended steps to take in order to verify, secure and prevent the ImageMagick vulnerability until the patch will be available?

Answer 1

As per the page you linked, there's a workaround.

Add the following to your policy.xml:

<policy domain="coder" rights="none" pattern="EPHEMERAL" />
<policy domain="coder" rights="none" pattern="HTTPS" />
<policy domain="coder" rights="none" pattern="MVG" />
<policy domain="coder" rights="none" pattern="MSL" />
<policy domain="coder" rights="none" pattern="TEXT" />

This file can be found in /etc/ImageMagick/.

This prevents the ImageMagick coder modules from leveraging the access modules above, each of which are currently vulnerable to the command injection issue.

There are a number of documented PoCs for the bug over at the oss-security thread, which can be used as a check to validate whether the bug is still present after applying the workaround.

Here are a couple examples:

exploit.mvg

push graphic-context
viewbox 0 0 640 480
fill 'url(https://example.com/image.jpg"|ls "-la)'
pop graphic-context

exploit.svg

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
"http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg width="640px" height="480px" version="1.1"
xmlns="http://www.w3.org/2000/svg" xmlns:xlink=
"http://www.w3.org/1999/xlink">
<image xlink:href="https://example.com/image.jpg&quot;|ls &quot;-la"
x="0" y="0" height="640px" width="480px"/>
</svg>

Simply running convert against these will cause ls -la to be executed, the output of which will be displayed in your console if the vulnerability is present.

Answer 2

Here is a reference for you: https://imagetragick.com

According to that page, you should verify magic bytes for the file you are processing, and you should use a policy file to disable the vulnerable ImageMagick coders.

The site provides a sample global policy. However it is not one size fits all. You can use it as a starting point.