Since WordPress 4.2 was released, some users are questioning why their sites have automatically updated to WordPress 4.1.3. There’s no information about the release on the Make WordPress Core site or the official WordPress news blog. However, this Codex article explains what’s in 4.1.3 and the reason it was released.
Fix database writes for esoteric character sets, broken in the WordPress 4.1.2 security release. Neither UTF-8 nor latin1 were affected. For more information, see ticket #32051.
The ticket contains a lengthy technical discussion of a critical bug and what was done to fix it. In addition to 4.1.3, the patch was merged into the following versions:
Since these are point releases, sites running WordPress 3.7 and higher will automatically update unless the server doesn’t support it or they’re disabled. If you’re running an old version of WordPress, I highly encourage you to update to 4.2. Not only does it have some nifty new features, but it also fixes 231 defects.
Source: WP Tavern