<p>That <code>cURL 51</code> error usually means that your server doesn't understand the <a href="https://en.wikipedia.org/wiki/Server_Name_Indication" rel="nofollow noreferrer">SNI SSL</a> certificate we have installed at <a href="https://craftcms.com" rel="nofollow noreferrer">https://craftcms.com</a> and <a href="https://craftcdn.com" rel="nofollow noreferrer">https://craftcdn.com</a>.</p>

<p>Technically there are 3 things a server needs to recognize SNI SSL certs:</p>

<ol>
<li><p>Using a version of cURL that supports it, at least 7.18.1 (8 years old: <a href="https://curl.haxx.se/changes.html" rel="nofollow noreferrer">https://curl.haxx.se/changes.html</a>)</p></li>
<li><p>Using a version of cURL compiled against a library that supports SNI, e.g. OpenSSL 0.9.8j (depending on the compilation options some older versions. 7 years old: <a href="https://www.openssl.org/news/changelog.html" rel="nofollow noreferrer">https://www.openssl.org/news/changelog.html</a>)</p></li>
<li><p>Using TLS 1.0 at least (not SSLv3)</p></li>
</ol>

<p>Once the box Craft is on meets those requirements, it should start working.</p>

CC BY-SA 3.0
2017-03-13T22:37:17.720Z
2017-03-13T22:37:17.720Z
Brad Bell
<p>When trying to upgrade Craft CMS automatically we get a message relative to the SSL certificate of the CDN being incorrect, though it works fine on a local machine. </p>

<blockquote>
  <p>Craft was unable to install this update :(</p>
  
  <p>[curl] 51: SSL: no alternative certificate subject name matches target
  host name 'download.craftcdn.com' [url]
  <a href="https://download.craftcdn.com/craft/2.6/2.6.2967/Patch/2.6.2962/41d682834df8c739ead7a1abab6a4571.zip" rel="nofollow noreferrer">https://download.craftcdn.com/craft/2.6/2.6.2967/Patch/2.6.2962/41d682834df8c739ead7a1abab6a4571.zip</a></p>
</blockquote>

<p>Anybody else getting this? </p>

<error-message>
Problem upgrading Craft CMS?
# Problem upgrading Craft CMS?

(Asked by: username_0 on 2017-03-13)

When trying to upgrade Craft CMS automatically we get a message relative to the SSL certificate of the CDN being incorrect, though it works fine on a local machine.

> Craft was unable to install this update :(
>
> [curl] 51: SSL: no alternative certificate subject name matches target
> host name 'download.craftcdn.com' [url]
> <https://download.craftcdn.com/craft/2.6/2.6.2967/Patch/2.6.2962/41d682834df8c739ead7a1abab6a4571.zip>

Anybody else getting this?

**Tags:** error-message

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## 1 answers

### Answer by username_1 on 2017-03-13. Score: 1

That `cURL 51` error usually means that your server doesn't understand the [SNI SSL](https://en.wikipedia.org/wiki/Server_Name_Indication) certificate we have installed at <https://craftcms.com> and <https://craftcdn.com>.

Technically there are 3 things a server needs to recognize SNI SSL certs:

1. Using a version of cURL that supports it, at least 7.18.1 (8 years old: <https://curl.haxx.se/changes.html>)
2. Using a version of cURL compiled against a library that supports SNI, e.g. OpenSSL 0.9.8j (depending on the compilation options some older versions. 7 years old: <https://www.openssl.org/news/changelog.html>)
3. Using TLS 1.0 at least (not SSLv3)

Once the box Craft is on meets those requirements, it should start working.


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