[Bug]: Some SVG files uploaded as logo make the server so slow it's unusable.

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

TLDR : Some svg files uploaded in theme page make nextcloud spawn deadloop threads. There must be a check on image file upload confirming that it could be processed properly.

Symptoms : many php8.1-fpm thread that runs 100% cpu for very long time. All the server become sluggish for while, users complain.

After many hours of investigation, different tries over many days. Install of different PHP version, settings, file by file comparaison of two servers (one with the bug, the other is ok), activating apps one by one, and many other things. I found the error.
Each page load in admin console spawns a new buggy thread.
The thread top one core at 100% until php fpm max execution time.

This was the url that spawns the buggy thread : index.php/apps/theming/icon/settings?v=34

The thread has a handle on a tmp file :
#lsof -p #PID# | grep tmp

/tmp/magick-15561EyX140DZCYQ2

There were zilion of those files, all the same content. It's an svg file.

It was the logo in theming page.

The file is

Also, this error was preventing the test mail from being sent...

It appears on PHP8.1 PHP8.2, debian, apache...

Steps to reproduce

1. upload the file as a theme logo
2. refresh admin console
3. watch the php-fpm thread go to 100% CPU for one hour :)
4. refresh again to spawn other buggy threads and watch your server crawl

Expected behavior

Rejecting files that could not be properly processed.
Even if this bug is in imagemagick nextcloud must be sure to work fine anyways.

Installation method

Community Web installer on a VPS or web space

Nextcloud Server version

26

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.2

Web server

Apache (supported)

Database engine version

MariaDB

Is this bug present after an update or on a fresh install?

Fresh Nextcloud Server install

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

not relevant

List of activated Apps

not relevant

Nextcloud Signing status

not relevant

Nextcloud Logs

not relevant

Additional info

I love you all :)

Start at the admin console path index.php/apps/theming/icon/settings?v=34 and trace how the uploaded theme logo is processed. Reproduce with the reported SVG, then verify that refreshing the admin console does not create prolonged 100% CPU PHP-FPM threads or repeated temporary files. Done means the problematic file is rejected or handled without making the server unusable.