It was discovered by Ken Milnore that xrdp 0.6.1 and earlier, when
validating user accounts against plain passwd files or via
shadow-utils, does not check for NULL returns from crypt(). [1]

--- sesman/verify_user.c ---
  encr = crypt(pass,salt);
  if (g_strncmp(encr, hash, 34) != 0)
  {
    return 0;
  }
  return 1;
----------------------------

A NULL return crashes the xrdp-sesman daemon resulting in an xrdp
server denial of service (for all modules that use xrdp's session
manager for user authentication via old-style passwd files or via
shadow passwords).

This has been fixed by upstream in its development branch. [2]

[1] http://sourceforge.net/p/xrdp/mailman/message/32985523/
[2] https://github.com/neutrinolabs/xrdp/commit/851c762ee722