https://mojang.com/2015/05/minecraft-1-8-5-security-release/
Notable fixes in 1.8.6:
[Bug MC-75630] – Exploit with signs and command blocks
==============================================================================
We have released a new version of Minecraft 1.8, called 1.8.5, which is now
available for download in your launcher. This release fixes a few reported
security issues, in addition to some other bug fixes.
This version is fully compatible with all previous 1.8 versions, but it is
still highly recommend to update to 1.8.5 as soon as possible.
Notable fixes:
[Bug MC-79632] – Phantom Custom Player in Scoreboard / UUIDs of
non-player entities on scoreboards truncated after relog
[Bug MC-75630] – Exploit with signs and command blocks
[Bug MC-80478] – Better server validation for movement packets
[Bug MC-80479] – Invalid beacon effects are not validated
[Bug MC-80480] – Certain attribute values are not bound