Unknown POST requests to website

I check error logs for my website. I found 17K error 400 with this message:

exception 'CHttpException' with message 'The CSRF token could not be verified.' REQUEST_URI=/D5D0B388-C7A5-6C4E-9000-4F3FC2C4F96B/6F69959E-D581-5F4E-BF2A-788F0344B177/from

Question - what is this? My web site have not links to "/D5D0B388-C7A5-6C4E-9000-4F3FC2C4F96B/6F69959E-D581-5F4E-BF2A-788F0344B177/from" and do not send POST request for this URI.