title: Cloudflare: Suddenly getting 403 if CDN is enabled
body: <p>I put my site behind Cloudflare last week and it has been working well. But today I woke up to an error message that my site is not accessible.</p>
  
  <p>I am getting generic nginx 403 page when I am trying to access my site (same as <a href="https://community.cloudflare.com/t/why-403-forbidden-all-of-a-sudden-when-i-go-to-my-site/3453" rel="nofollow noreferrer">https://community.cloudflare.com/t/why-403-forbidden-all-of-a-sudden-when-i-go-to-my-site/3453</a>), along with 'not secure' warning in Chrome address bar.</p>
  
  <p>When I disable CDN as shown in the picture, the error disappears.
  <a href="https://i.stack.imgur.com/Qc6L3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Qc6L3.png" alt="enter image description here"></a></p>
  
  <p>I am using an SSL cert issued by Letsencrypt in my server and a Full SSL in Cloudflare. I can confirm that Letsencrypt cert has not been expired.</p>
  
  <p><a href="https://i.stack.imgur.com/jN7xs.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/jN7xs.png" alt="enter image description here"></a></p>
  
  <p>Any ideas how to debug this issue? I am confused as to why it was working and suddenly stopped working when nothing changed.</p>
  
  <hr>
  
  <p><strong>Additional information</strong></p>
  
  <p>When I enable the CDN, I get the following error(<code>ERR_CERT_COMMON_NAME_INVALID</code>) in Chrome's security tab:</p>
  
  <p><a href="https://i.stack.imgur.com/0QacB.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0QacB.png" alt="enter image description here"></a>
  <a href="https://i.stack.imgur.com/P7jtp.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/P7jtp.png" alt="enter image description here"></a></p>
  
  <p>The error I get when I <code>curl</code> the https version of the site is:</p>
  
  <pre><code>curl: (51) SSL: no alternative certificate subject name matches target host name 'my-domain.com'
  </code></pre>