Why does yum fail with error "/usr/local/lib/libcurl.so.4 undefined symbol MD5_Init" in Red Hat Enterprise Linux?

Issue

• yum fails with the following traceback.

[root@test ~]# yum repolist
There was a problem importing one of the Python modules
required to run yum. The error leading to this problem was:

   /usr/local/lib/libcurl.so.4: undefined symbol: MD5_Init

Please install a package which provides this module, or
verify that the module is installed correctly.

It's possible that the above module doesn't match the
current version of Python, which is:
2.6.6 (r266:84292, Aug  9 2016, 06:11:56)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-17)]

If you cannot solve this problem yourself, please go to
the yum faq at:
  http://yum.baseurl.org/wiki/Faq