GraphicsMagick Security

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# GraphicsMagick Security

# Background

Although GraphicsMagick is image processing software, security is a very important consideration for GraphicsMagick. GraphicsMagick may be used to open files and URLs produced by an untrusted party. Given a suitable weakness (which we make every effort to prevent), an intentionally constructed file might be able to cause the software to crash, leak memory, request huge amounts of memory, run forever, or in the worst case execute arbitrary code, including shell code. GraphicsMagick is very powerful and complex software supporting many capabilities and so untrusted parties should never be allowed to submit arbitrary requests into it.

GraphicsMagick includes the ability to access arbitrary http and ftp URLs as well as local image, font, and SVG files. The SVG renderer supports read access to http and ftp URLs as well as local files according to the SVG specification. Since URLs and local file paths may be included in SVG files, untrusted SVG files may create a Server Side Request Forgery (SSRF) vulnerability since URL requests are done by the computer executing the SVG, which may be in a realm of trust (e.g. inside the firewall and able to access "localhost" addresses).

The -comment, -draw, -format, and -label utility options support a @filename syntax to incorporate any readable file on the system as a convenience to the user. If text from an untrusted source (e.g. a web page) is allowed to supply these options, then they may be used to read arbitrary files, creating a potential security hazard.

The GraphicsMagick project is continually striving to eliminate conditions in the software which might pose a risk for its users while not constraining what its users may do with the software.

# Reporting Issues

If you become aware of a serious security issue with GraphicsMagick, then it may be addressed by email directly to the GraphicsMagick maintainers or to the GraphicsMagick Security mail address. More minor issues are best addressed via the GraphicsMagick Bug Tracker at SourceForge. Please remember to set the bug to 'private' if you use the bug tracker or else someone may acquire a zero-day exploit from your report. We will set the bug to 'public' as soon as a remedy has been made available.

Reporting an issue will allow us to fix it so that future releases of the software won't suffer from the problem.

The current state of free software is that security-sensitive free software projects have been undergoing automated testing by machines (and sometimes what might be hundreds of machines). Machines do not need to work at a day job, take care of families, rest, or eat, but we do. Any bug report which comes with a patch or changeset to fix the problem is greatly appreciated and helps to move the project forward.

The remedy available to us is to submit a changeset to the GraphicsMagick Mercurial repository, and include the changes in the next release. Regardless of how an issue becomes known to us, the issue will become public knowledge as soon as we commit a fix to the source code repository. Only in exceedingly rare and dire circumstances (e.g a previously-unknown zero-day shell exploit) might we do anything different.

# Safe Use Of The Software

You are the first line of defense when it comes to GraphicsMagick security!

If you are operating a server which supports file uploads from untrusted users, or delivered via a network protocol such as http, ftp, or email, then you should take steps to assure that a problem with opening/processing the file does not place the whole server at risk. These are steps which can be taken:

1. Subscribe to the graphicsmagick-announce mailing list so that you are informed about new GraphicsMagick releases or special security bulletins.

2. Make sure that GraphicsMagick is up to date as reported on the GraphicsMagick web site. Don't simply trust that packages from your operating system vendor are kept up to date or are updated to include security fixes. Keeping GraphicsMagick up to date might require that you compile GraphicsMagick yourself from source code.

3. Execute the software in a Container, FreeBSD Jail, Solaris Zone, or chrooted environment such that it can not cause harm to the system running it.

4. Execute the software as a least-privileged user (e.g. 'nobody').

5. Normalize input file names or any other external inputs so that they are under your control and not controlled by an untrusted party. This should include any file name specifications, which may include arbitrary 'glob' patterns (wildcards) (requiring hours or days to complete if sufficiently close long file names exist), and options supporting a @filename syntax.

6. Enforce that uploaded files are passed to the expected reader. For example, the uploaded file "file.jpg" is forced to be read by the JPEG reader (rather than a reader selected based on header magic testing) by using the file name "jpg:file.jpg". If the file is not really what was indicated, then an error is reported.

   GraphicsMagick supports a great many file types and auto-detects many file types based on their content rather than file extension. The file which pretends to be an ordinary PNG or JPEG file might be something else entirely. Note that even using independent file header testing may not be sufficient since it is possible to construct valid files with a header which appears to be several different types, but the first type which matches while testing the header will be selected.

7. Apply resource limits via the -limit option or the MAGICK_LIMIT_* environment variables (e.g. export MAGICK_LIMIT_PIXELS=30Mp, export MAGICK_LIMIT_MEMORY=500Mb). Also consider setting resource limits using the ulimit command.

8. Consider using the MAGICK_CODER_STABILITY environment variable to constrain the supported file formats to the subsets selected by PRIMARY or STABLE. After setting this environment variable (e.g. export MAGICK_CODER_STABILITY=PRIMARY), use gm convert -list format and verify that the format support you need is enabled. Selecting the PRIMARY or STABLE options blocks access of http and ftp URLs (SSRF vulnerability), but does not block SVG renderer access to read local image files.

# PGP Public Key

The following PGP public key (belonging to Bob Friesenhahn) is used to sign release files (there is an associated .sig file) and may be used for private correspondence:

    -----BEGIN PGP PUBLIC KEY BLOCK-----

    [encoded data, 9792 characters]
    akWaTz0WKIOiD9Lm2ylI9J0=
    =UAq2
    -----END PGP PUBLIC KEY BLOCK-----

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