Remote Code Execution in ImageMagick (CVE-2016–3714)

https://medium.com/@rhuber/imagemagick-is-on-fire-cve-2016-3714-379faf762247

by jwise0 • 10 years ago

30 8 10 years ago

chatmasta• 10 years ago

The article doesn't reveal much, but judging from the list of vulnerable coders and the fact that the Imagemagick forum post references the delegates.xml file, I imagine the exploit allows users to create their own delegate [0], then upload an image that causes that delegate to be called. My guess is that the exploit is two parts: 1) appending a line to the delegates.xml file by exploiting a vulnerable coder, and 2) exploiting the custom delegate you create.

Delegates seem very dangerous and there's all sorts of ways to exploit a custom delegate.

I'm surprised we haven't seen more Imagemagick vulnerabilities... it's a really old library with a massive codebase supporting tons of file formats and arbitrary command chaining. And it's often called by higher level languages via functions like `system()` or `shell()` where developers could easily neglect to "properly sanitize" user inputs, since what those "inputs" can be is so wide ranging.

[0] http://www.imagemagick.org/Usage/files/#delegates

EDIT:

Looks like I was right... check out this commit from 3 days ago:

https://github.com/ImageMagick/ImageMagick/commit/06c41aba39...

"Sanitize input filename for http / https delegates"

So presumably the attack is to set the "filename" property of a file such that when including '%f' in a command, the filename breaks the shell command and inserts its own arbitrary code.

EDIT 2:

A reddit user also linked to this critical line: https://github.com/ImageMagick/ImageMagick/blob/e93e339c0a44...

So the process would be something like this:

1) Create file with name e.g. evilserver.com/funnycat';rm-rf/;.gif hosted on remote server

2) Somehow instruct vulnerable imagemagick install to download evilserver.com/funnycat';rm-rf/;.gif

3) Assume 99% chance that the render command on server will include %f, which is unsanitized, and will cause rm -rf / to execute

I'm a bit confused on step (2)... how do you tell imagemagick to download a file? Will this only affect installations that are explicitly downloading untrusted URLs from users? Like if imgur "upload via URL" fed the URL directly to imagemagick, it would be vulnerable...

asteadman• 10 years ago

I assume Lambda is affected? According to http://docs.aws.amazon.com/lambda/latest/dg/current-supporte..., Lambda functions have access to ImageMagick-6.7.8.9. I'm not sure how you can specify a policy file in such an environment.

barnybug• 10 years ago

Yes, confirmed ImageMagick on Lambda is vulnerable.

michaelmcmillan• 10 years ago

https://github.com/ImageMagick/ImageMagick/commit/e93e339c0a...

oneweekwonder• 10 years ago

Any insight?

alxndr2• 10 years ago

No insight, but the diff is easier to look at if you tell GitHub to ignore (most) whitespace with `?w=1`: https://github.com/ImageMagick/ImageMagick/commit/e93e339c?w...

Remote Code Execution in ImageMagick (CVE-2016–3714)

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