Is there a patch for SA-CORE-2018-002?
Per the official the FAQ about SA-CORE-2018-002:


  I manage a Drupal 6 site, is a fix available?
  
  Yes, Drupal 6 is also affected and the Drupal 6 Long Term Support project has patches available.


The issue for this is [core] Add D6LTS patch for SA-CORE-2018-002.  The issue has a patch from a security team member and further information.

2018-03-30 update:

Per a security team member in a recent comment:


  Please just upgrade Drupal core rather than patching!
  
  Note also the D6lts patch and corresponding github releases for that
  and Pressflow 6 were updated to fix a subtle flaw in the released
  security fix that was affecting a couple contrib modules including
  Organic Groups (og) for Drupal 6.
  
  https://github.com/d6lts/drupal/releases/tag/6.43
  
  https://github.com/pressflow/6/releases/tag/pressflow-6.43.124