PDF attachments cannot be displayed if the file extension is in uppercase

[StefInP]

Steps to reproduce

1. Receiving an email with a PDF attachment whose file extension is in uppercase (*.PDF)
2. Try to open the attachment : Nothing happens

This behavior occurs from the message list or the message view.
No problem with lowercase file extensions (*.pdf).

Expected behavior

The PDF file should open.

Actual behavior

See above steps to reproduce.

Mail app version

5.7.15

Nextcloud version

33.0.3

Mailserver or service

Mailo

Operating system

Linux 6.12.86+deb13-cloud-amd64 x86_64

PHP engine version

PHP 8.3

Nextcloud memory caching

No response

Web server

Apache (supported)

Database

PostgreSQL

Additional info

Instance AIO 13.0.3

[ChristophWurst]

Thanks for the report

This is not reproducible by just sending a .PDF attachment to myself. There must be an additional condition.

Please inspect the source of the email and share the attachment part headers. Mine were

Content-Type: application/pdf; name="TEST.PDF"
Content-Disposition: attachment; filename="TEST.PDF"
Content-Transfer-Encoding: base64
...

[StefInP]

Hi @ChristophWurst
My attachment part headers :

Content-Type: application/octet-stream;
	name="=?ISO-8859-1?Q?Ticket_facture_n=B04754=5F1=2EPDF?="
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
	filename="=?ISO-8859-1?Q?Ticket_facture_n=B04754=5F1=2EPDF?="

By replacing Content-Type: application/octet-stream with Content-Type: application/pdf, the attachment opens normally.
There appears to be an issue with the email header.
However, the original attachment opens normally in Thunderbird and the mail provider webmail.

[ChristophWurst]

Thanks! We handle the mime types defensively. If the attachment is said to be an application, we don't bother loading it into the PDF viewer.
I think for security reasons that is a sane, but of course it can hurt UX in cases like yours.

I'm undecided if this should change.

[ChristophWurst]

I will discuss this internally.