Open_basedir warnings on Classic Post edit screens with TinyMce plugins present, like TinyMce Advanced

[rembem]

On Post Edit screens in the backend, multiple of these 2 PHP Warnings are triggered in the conditions described below:

is_file(): open_basedir restriction in effect. File(/en.js) is not within the allowed path(s): 
is_file(): open_basedir restriction in effect. File(/en_dlg.js) is not within the allowed path(s):

These warnings are triggered when:

1. Open BaseDir restrictions are present on the server.
2. Classic Editor plugin is used. Possibly also with Classic block in the block editor (not tested)
3. There is a plugin or theme that adds functionality/buttons to TinyMCE, for example if it adds one or more buttons to the editor. This happens for example when the plugin Advanced Editor Tools (previously TinyMCE Advanced) is installed. Many themes add shortcodes to the editor as buttons/dropdowns, etc.

The warnings are caused by line 513 of wp-includes/class-wp-editor.php:

$path = trailingslashit( realpath( $path ) );

Here is checked if a /langs/ path is present for the TinyMCE plugin.
If no /langs/ path is not present, realpath() returns false, resulting in a $path passed to is_file() that is outside the Open BaseDir allowed paths.

A solution would be to build in a check: not check the language paths, if realpath() === false.

Notes:

• I see these warning with Query Monitor Plugin. See attached screenshot
• Possibly the warnings are also triggered in the block editor with the Classic block. Did not check. Also because Advanced Editor Tools (previously TinyMCE Advanced) is not working well yet with WP5.8.
• The warnings are also there in WP 5.7.x as suppressed warnings.
• The warnings are suppressed in PHP7.x, but not in PHP8

[rembem]

Screenshot QueryMonitor PHP warning

[MadtownLems]

I'm experiencing the same errors. For me, they don't even need the Classic Editor. I'm getting them on a brand new post with the Block Editor.

It's caused by a very small custom plugin that enables rich text editing for Post Excerpts. Never saw the error before upgrading to PHP8/PHPFPM.

(Note: the error is on 6.0.3, but I can't select a version that high)

[MadtownLems]

Patch to fix attempts at opening non-existent language files that throw errors in some configurations

[MadtownLems]

Tagging as "has-patch"

[njsamsatli]

Hi, thanks for this. I have the same error messages and applying the patch fixed it for me. Just wondering if this will make it into the next release and whether it's safe for me to keep the patch on my site.

[azaozz]

54354.diff looks okay imho. 54354.1.diff just saves the call to trailingslashit() if the directory doesn't exist or is not readable.

[azaozz]

Re-testing this, seems to work fine and solve the reported problems.

[azaozz]

In 56235:

Editir: Fix open_basedir warnings on the classic Edit Post screen when additional TinyMCE plugins are used.

Props: rembem, MadtownLems, njsamsatli, sabernhardt, azaozz.
Fixes: #54354.