403 Forbidden on a couple of WordPress admin pages

[seezee]

System

• Ubuntu Bionic hosted on GPC
• WordPress 5.4.2
• mod_sec not intalled

403 Forbidden when accessing Add New Plugin (/wp-admin/plugin-install.php) and also when opening modal for plugin update information (e.g., /wp-admin/plugin-install.php?tab=plugin-information&plugin=my_plugin&section=changelog&TB_iframe=true&width=772&height=1167).

Using the same setup on 3 other websites without error. Permissions are correct (0644, owned by the webserver user). Temporarily disabled all plugins to see if any of them were causing it. Cleared all caches, locally and Cloudflare. Still no joy.

Not finding anything in the logs.

 

[Cold-Egg]

Please also share the error log under /usr/local/lsws/logs/, it should shows something when you accessing Add New Plugin

 

[seezee]

Last 100 lines of error log. Nothing useful as far as I can see. Note that I disabled the blackhole plugin (along with all other plugins) previously and still got the 403 error.

Accessed the page, then ran TAIL on the log immediately. Some paths altered for security:

 

[Cold-Egg]

Maybe some of the plugin either changed the file/folder permission or path. Basically LSWS and LSCache plugin have no such function.
Right, no important msg in the error log you provided.

 

[seezee]

Permissions and ownership are correct (0644, www-data). So are the paths. No redirect happening either.

Is there another log I could look at that might show the 403 error with more detailed explanation?