I just released Chef Zero 1.6.3. There’s a 99% probability this won’t affect you, since the latest stable is 2.0 and the version in Chef Client in 1.7. However, there was a critical bug that affects Chef Client < 11.8 with respect to JSON parsing. This has been fixed in 1.7 and 2.0 for some time, but was never backported to the 1.6 series.
If you are using Chef Client 11.10 you can disregard this release :).
Release Engineer, Chef