When i am trying to go to resource pages of CS50 like syllabus link

I get untrusted page error by my browsers firefox and opera and cant even make an exception here is the error i get, this has been happening since yesterday wasnt a problem before.

This Connection is Untrusted

You have asked Firefox to connect securely to cdn.cs50.net, but we can't confirm that your connection is secure.

Normally, when you try to connect securely, sites will present trusted identification to prove that you are going to the right place. However, this site's identity can't be verified. What Should I Do?

If you usually connect to this site without problems, this error could mean that someone is trying to impersonate the site, and you shouldn't continue.

This site uses HTTP Strict Transport Security (HSTS) to specify that Firefox only connect to it securely. As a result, it is not possible to add an exception for this certificate.

cdn.cs50.net uses an invalid security certificate. The certificate is only valid for the following names: cloudfront.net, *.cloudfront.net (Error code: ssl_error_bad_cert_domain)

  • I can get there with Chrome using not private connection.
    – user2477
    Feb 24 '15 at 16:51
  • 1
    Thanks Alexandr, I really try to avoid chrome it makes my system hang everytime I use chrome with more than 5 tabs. (Ubuntu)
    – Anjan
    Feb 25 '15 at 3:32

Try to access that page via cs50 official website: http://cs50.net. If you click on syllabus you get similar page (do not know if it is exactly the same) with the following link http://cdn.cs50.net/2015/spring/lectures/0/w/syllabus/syllabus.html. This link is a little different than yours, and it does not have any security related questions.

  • the problem is also with other pages like pset one and other resources.
    – Anjan
    Feb 26 '15 at 13:43
  • @Anjan : Check with your ISP. They may block or restrict access to certain pages accordingly to the law of your country.
    – user2477
    Feb 26 '15 at 14:18
  • its not an issue with ISP its with firefox i suppose, cause i can view same page with opera.
    – Anjan
    Feb 28 '15 at 6:12

I understand the risks -> Add an exception

  • doesnt work.. i can view the page with oerabut not with firfox
    – Anjan
    Feb 28 '15 at 6:11
  • Please describe what happens after you do that actions requested. does not work is not informative enough. Feb 28 '15 at 13:05
  • 1
    Hi I just updated Ubuntu and reinstalled my firefox now it is giving me an option to add exception, previously it wasnt. Now after adding the exception I can view the web page. Thankyou
    – Anjan
    Mar 1 '15 at 6:14


This has been resolved in the comments.

The fix was to apt-get update && apt-get upgrade Ubuntu, and upgrade Firefox to the latest version,

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