A site for a client is running ecart 5.0.3. Authorize.net is cutting off all payments using SSLv3 on 11-4 for he POODLE security issue. I need to know that this will not be an issue for my client.

n/a

As far as the eCart code goes, there will not be an issue.

That is not to say there _wont_ be an issue, there could still be one.

the poodle vulnerability is not at the code level, it is at the server configuration level and at the client Browser level.

You should contact your host and make sure that they have taken precautions to disable SSLv3 on the server, specifically in the cURL configuration settings.

also, in the browsers that people are using to browse your site, they will need to make sure the browser is not vulnerable to the poodle attack by updating to the most recent versions.

This article has some good resources:
http://chrisburgess.com.au/how-to-test-for-the-sslv3-poodle-vulnerability/