Image Magick 0 Day Threat

Vulnerability

Image Magick has a potential vulnerability noted by http://www.openwall.com/lists/oss-security/2016/05/03/18

 

Basically in short the exploit allows commands to be run remotely when passed via curl or a URL. To see if you are vulnerable try running the following command on your server:

convert 'https://example.com"| ls "-la' out.png

If you successfully list the directory then you are vulnerable.

 

The Fix

The quick easy fix for this is to adjust your policy.xml file, which depending on version installed will either be in /etc/ImageMagick/policy.xml (in versions 6.6 and newer of ImageMagick or /usr/lib64/ImageMagick/config/policy.xml in versions 6.5.x and older. Simply paste the following in your policymap section:

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

Once you’ve made the necessary adjustments run the test from above again and it should be denied.

Entire Policy.xml

If you need a better contextual example below is a policy.xml file containing the fix:

 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE policymap [
<!ELEMENT policymap (policy)+>
<!ELEMENT policy (#PCDATA)>
<!ATTLIST policy domain (delegate|coder|filter|path|resource) #IMPLIED>
<!ATTLIST policy name CDATA #IMPLIED>
<!ATTLIST policy rights CDATA #IMPLIED>
<!ATTLIST policy pattern CDATA #IMPLIED>
<!ATTLIST policy value CDATA #IMPLIED>
]>
<!--
  Configure ImageMagick policies.
  Domains include system, delegate, coder, filter, path, or resource.
  Rights include none, read, write, and execute.  Use | to combine them,
  for example: "read | write" to permit read from, or write to, a path.
  Use a glob expression as a pattern.
  Suppose we do not want users to process MPEG video images:
    <policy domain="delegate" rights="none" pattern="mpeg:decode" />
  Here we do not want users reading images from HTTP:
    <policy domain="coder" rights="none" pattern="HTTP" />
  Lets prevent users from executing any image filters:
    <policy domain="filter" rights="none" pattern="*" />
  The /repository file system is restricted to read only.  We use a glob
  expression to match all paths that start with /repository:
    <policy domain="path" rights="read" pattern="/repository/*" />
  Any large image is cached to disk rather than memory:
    <policy domain="resource" name="area" value="1gb"/>
  Note, resource policies are maximums for each instance of ImageMagick (e.g.
  policy memory limit 1GB, -limit 2GB exceeds policy maximum so memory limit
  is 1GB).
-->
<policymap>
  <!-- <policy domain="system" name="precision" value="6"/> -->
  <!-- <policy domain="resource" name="temporary-path" value="/tmp"/> -->
  <!-- <policy domain="resource" name="memory" value="2GiB"/> -->
  <!-- <policy domain="resource" name="map" value="4GiB"/> -->
  <!-- <policy domain="resource" name="area" value="1gb"/> -->
  <!-- <policy domain="resource" name="disk" value="16eb"/> -->
  <!-- <policy domain="resource" name="file" value="768"/> -->
  <!-- <policy domain="resource" name="thread" value="4"/> -->
  <!-- <policy domain="resource" name="throttle" value="0"/> -->
  <!-- <policy domain="resource" name="time" value="3600"/> -->
  <policy domain="coder" rights="none" pattern="EPHEMERAL" />
  <policy domain="coder" rights="none" pattern="URL" />
  <policy domain="coder" rights="none" pattern="HTTPS" />
  <policy domain="coder" rights="none" pattern="MVG" />
  <policy domain="coder" rights="none" pattern="MSL" />
</policymap>

 

 

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