[imp] PDF thumbnails no longer working

[Arjen de Korte]

Citeren Arjen de Korte <build+horde at de-korte.org>:

> Citeren Arjen de Korte <build+horde at de-korte.org>:
>
>> Just recently, I noticed thumbnails for PDF attachments now show as  
>> a black questionmark on a white background. Other attachments (JPG  
>> files for instance) still show correct thumbnails, so I guess the  
>> imagick PECL extension is still doing its job.
>>
>> imp = 6.2.22
>> Horde_Core = 2.31.6
>> Horde_Pdf = 2.0.7
>> php7-imagick = 3.4.3
>> ImageMagick = 7.0.8
>>
>> Am I the only one where this seems to be broken?
>
> Answering to myself: it turns out the distribution I use (openSUSE  
> Tumbleweed) nowadays ships with a policy.xml file for ImageMagick  
> that prevents reading PDF files. Changing the policy from 'none' to  
> 'read' fixed the generation of thumbnails.

Again answering to myself again. After looking up why PDFs are not an  
acceptable input format for ImageMagick anymore, it turns out this was  
switched off to address a vulnerability in Ghostscript:

     https://www.kb.cert.org/vuls/id/332928

So the above suggestion to re-enable it in the 'policy.xml' may not be  
safe depending on which Ghostscript version is currently installed on  
your system.

Another way to deal with the ugly PDF thumbnails that are generated  
now, is to switch off thumbnails for PDF files in  
'imp/config/mime_drivers.local.php':

     <?php
     $mime_drivers['pdf']['thumbnails'] = false;

Choose your poison.