Dompdf's usage of vulnerable version of phenx/php-svg-lib leads to restriction bypass and potential RCE
### Summary
A lack of sanitization/check in the font path returned by php-svg-lib, in the case of a inline CSS font defined, that will be used by Cpdf to open a font will be passed to a `file_exists` call, which is sufficient to trigger metadata unserializing on a PHAR file, through the phar:// URL handler on PHP < 8.0. On other versions, it might be used as a way to get a SSRF through, for example, ftp, not restricted by authorized protocols configured on dompdf.
### Details
The problem lies on the `openFont` function of the `lib/Cpdf.php` library, when the `$font` variable passed by php-svg-lib isn't checked correctly. A path is crafted th
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