What versions of OS X are affected by Heartbleed?
No versions of OS X are affected (nor is iOS affected). Only installing a third party app or modification would result in a Mac or OS X program having that vulnerability / bug in OpenSSL version 1.0.x



Apple deprecated OpenSSL on OS X in December of 2012 if not earlier. No version of OpenSSL that is vulnerable to CVE-2014-0160 (a.k.a the Heartbleed Bug)

Apple provides several alternate application interfaces that provide SSL to Mac developers and has this to say about OpenSSL:


  OpenSSL does not provide a stable API from version to version. For this reason, although OS X provides OpenSSL libraries, the OpenSSL libraries in OS X are deprecated, and OpenSSL has never been provided as part of iOS. Use of the OS X OpenSSL libraries by apps is strongly discouraged.


Specifically, the latest version of OpenSSL shipped by Apple is OpenSSL 0.9.8y 5 Feb 2013 which does not appear to have the bug from newer versions of OpenSSL back ported to the code for Apple's version of the library.

The PDF of this documentation has some clearly written advice for developers and some sections that's useful for professionals or the security minded user as well.


OpenSSL for Mac Developers and PDF version of Apple's Cryptographic Services Guide


Considering this, the only remaining issue would be additional software that were built against OpenSSL, e.g. several in Homebrew (brew update followed by brew upgrade) or MacPorts (port self update followed by port upgrade openssl) to update to the patched 1.x version of openSSL.

Also, you could use mdfind/mdls to check on files named openssl in case you have other applications that bundle that library as Apple recommends rather than depending on the "safe" version Apple still ships with OS X.

for ff in `mdfind kMDItemFSName = "openssl"`; do echo "#### $ff"; mdls $ff | grep kMDItemKind; done