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fix(sec): Overwrite ImageMagick's security policy to tighten it up (part1) #811

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Merged
antobinary merged 1 commit into from
Dec 2, 2025
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fix(sec): Overwrite ImageMagick's security policy to tighten it up (part1) #811

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113 changes: 113 additions & 0 deletions bbb-install.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -126,6 +126,8 @@ main() {
GL3_DIR=~/greenlight-v3
LTI_DIR=~/bbb-lti
NGINX_FILES_DEST=/usr/share/bigbluebutton/nginx
IMAGE_MAGICK_DIR=/etc/ImageMagick-6
OVERWRITE_IMAGE_MAGICK_POLICY=true
CR_TMPFILE=$(mktemp /tmp/carriage-return.XXXXXX)
printf '\n' > "$CR_TMPFILE"

Expand Down Expand Up @@ -391,6 +393,117 @@ main() {
install_greenlight_v3
fi

if [ "$OVERWRITE_IMAGE_MAGICK_POLICY" = true ]; then
echo "ATTENTION!!"
echo "Overwriting ImageMagick policy file (modifying the default configuration to seal security vectors)"

#
# This is the imagemagick-provided https://imagemagick.org/source/policy-websafe.xml with
# minimal modifications required for bigbluebutton presentation conversion to work


cat <<HERE > "$IMAGE_MAGICK_DIR/policy.xml"
<!--
Creating a security policy that fits your specific local environment
before making use of ImageMagick is highly advised. You can find guidance on
setting up this policy at https://imagemagick.org/script/security-policy.php,
and it's important to verify your policy using the validation tool located
at https://imagemagick-secevaluator.doyensec.com/.
Web-safe ImageMagick security policy:
This security protocol designed for web-safe usage focuses on situations
where ImageMagick is applied in publicly accessible contexts, like websites.
It deactivates the capability to read from or write to any image formats
other than web-safe formats like GIF, JPEG, and PNG. Additionally, this
policy prohibits the execution of image filters and indirect reads, thereby
thwarting potential security breaches. By implementing these limitations,
the web-safe policy fortifies the safeguarding of systems accessible to
the public, reducing the risk of exploiting ImageMagick's capabilities
for potential attacks.
-->
<policymap xmlns="">
<!-- Set maximum parallel threads. -->
<policy xmlns="" domain="resource" name="thread" value="2"/>
<!-- Set maximum time to live in seconds or neumonics, e.g. "2 minutes". When
this limit is exceeded, an exception is thrown and processing stops. -->
<policy xmlns="" domain="resource" name="time" value="60"/>
<!-- Set maximum number of open pixel cache files. When this limit is
exceeded, any subsequent pixels cached to disk are closed and reopened
on demand. -->
<policy xmlns="" domain="resource" name="file" value="768"/>
<!-- Set maximum amount of memory in bytes to allocate for the pixel cache
from the heap. When this limit is exceeded, the image pixels are cached
to memory-mapped disk. -->
<policy xmlns="" domain="resource" name="memory" value="256MiB"/>
<!-- Set maximum amount of memory map in bytes to allocate for the pixel
cache. When this limit is exceeded, the image pixels are cached to
disk. -->
<policy xmlns="" domain="resource" name="map" value="512MiB"/>
<!-- Set the maximum width * height of an image that can reside in the pixel
cache memory. Images that exceed the area limit are cached to disk. -->
<policy xmlns="" domain="resource" name="area" value="16KP"/>
<!-- Set maximum amount of disk space in bytes permitted for use by the pixel
cache. When this limit is exceeded, the pixel cache is not be created
and an exception is thrown. -->
<policy xmlns="" domain="resource" name="disk" value="1GiB"/>
<!-- Set the maximum length of an image sequence. When this limit is
exceeded, an exception is thrown. -->
<policy xmlns="" domain="resource" name="list-length" value="16"/>
<!-- Set the maximum width of an image. When this limit is exceeded, an
exception is thrown. -->
<policy xmlns="" domain="resource" name="width" value="4KP"/>
<!-- Set the maximum height of an image. When this limit is exceeded, an
exception is thrown. -->
<policy xmlns="" domain="resource" name="height" value="4KP"/>
<!-- Periodically yield the CPU for at least the time specified in
milliseconds. -->
<policy xmlns="" domain="resource" name="throttle" value="2"/>
<!-- Do not create temporary files in the default shared directories, instead
specify a private area to store only ImageMagick temporary files. -->
<!-- <policy domain="resource" name="temporary-path" value="/magick/tmp/"/> -->
<!-- Force memory initialization by memory mapping select memory
allocations. -->
<policy xmlns="" domain="cache" name="memory-map" value="anonymous"/>
<!-- Ensure all image data is fully flushed and synchronized to disk. -->
<policy xmlns="" domain="cache" name="synchronize" value="true"/>
<!-- Replace passphrase for secure distributed processing -->
<!-- <policy domain="cache" name="shared-secret" value="secret-passphrase" stealth="true"/> -->
<!-- Do not permit any delegates to execute. -->
<policy xmlns="" domain="delegate" rights="none" pattern="*"/>
<!-- Do not permit any image filters to load. -->
<policy xmlns="" domain="filter" rights="none" pattern="*"/>

<!-- Don't read/write from/to stdin/stdout. -->
<policy xmlns="" domain="path" rights="none" pattern="-"/>

<!-- Indirect reads are not permitted. -->
<policy xmlns="" domain="path" rights="none" pattern="@*"/>

<!-- don't read sensitive paths. -->
<policy domain="path" rights="none" pattern="/*"/>

<!-- allow access to required paths. -->
<policy domain="path" rights="read|write" pattern="/var/bigbluebutton/*"/>
<policy domain="path" rights="read|write" pattern="/tmp/*"/>

<!-- Deny all image modules and specifically exempt reading or writing
web-safe image formats. -->
<policy xmlns="" domain="module" rights="none" pattern="*"/>
<policy domain="module" rights="read | write" pattern="{BMP,GIF,JPEG,PDF,PNG,TIFF,WEBP}"/>
<policy xmlns="" domain="module" rights="read | write" pattern="{MPC}" stealth="true"/>
<policy domain="module" rights="write" pattern="{JSON,INFO,PNM,PS,SVG}"/>
<!-- This policy sets the number of times to replace content of certain
memory buffers and temporary files before they are freed or deleted. -->
<policy xmlns="" domain="system" name="shred" value="1"/>
<!-- Enable the initialization of buffers with zeros, resulting in a minor
performance penalty but with improved security. -->
<policy xmlns="" domain="system" name="memory-map" value="anonymous"/>
<!-- Set the maximum amount of memory in bytes that are permitted for
allocation requests. -->
<policy xmlns="" domain="system" name="max-memory-request" value="256MiB"/>
</policymap>
HERE
fi

bbb-conf --check
}

Expand Down