[BlueOnyx:13280] cURL version / Wordpress problem?

[Wisja.net Computers]

Hi list,

We have 2 servers (identical) with many WordPress installations. The updates there
always worked correctly. Suddenly, a few months back all updates of major (!) plugins
(like Jetpack, WPML) including the WordPress core upgrade itself fail at:

Downloading update from http://...

Now this does not seem to be a regular update issue:
* The PHP memory limit is high enough (256MB). Also the memory has been sufficient until
now.
* The access writes are OK. We can check them via SSH. And many other minor plugins can
be updated without problems.
* The update file is downloaded alright each time. We can see it in the system tmp
folder. It is there in full size, but with "tmp" exception. Also (as I will explain
later) the process has not got to the point of unpacking it yet, so it is not an unzip
problem (and, remember, the minor plugins are updated correctly, so unzip works for them).
* This happens in all our WordPress installations in this server regardless of their
version. Ranging from 2.9 to 3.5. - We do not believe that our IP is somewhere
blacklisted. We can wget the files from the console and (as mentioned above) we see the
temporary files being downloaded. Also (again) minor plugins are updated correctly.

So the problem gets a little crazy. So we start hacking into the core code of WordPress.
We put debugging messages through every single step of the update process and we get
down to this:

The process gets to a point where (in file /wp-includes/class-http.php, around line
1140) it executes a PHP curl command to download the update. It does a curl_init, then
many curl_setopt calls and, finally a curl_exec.

Well this curl_exec never returns.

Then we try to debug the curl download so, after several tries, we add a progress
callback to it like this:

---

curl_setopt($handle, CURLOPT_NOPROGRESS, false);

---

And then, after this addition, the curl_exec finishes fine and the upgrade goes on
successfully!

PHP version 5.3.3 (stock), cURL version 7.19.7 (stock)

Any ideas? Is it possible to upgrade cURL, last update is 7.31?

Wisja