An XDA forums member by the name of christofsteel has succesfully used the Dirty COW vulnerability to root a 1st-gen Fire TV running software version 22.214.171.124. Prior to this, all Fire OS 3 versions between 126.96.36.199 and 188.8.131.52 were unrootable. The rooting procedure does not appear to work on devices running Fire OS 5, so this likely won’t be of any use to the vast majority of you who want to root your Fire TVs but are on unrootable software versions.
Devices running Fire OS 3 version 184.108.40.206 and up may be rootable with this method, but they would still be limited from downgrading due to the eFuse changes with those versions. Most devices running Fire OS 3 will actually still update to an earlier version of Fire OS 5 that is still rootable, instead of the latest unrootable version, so there’s little point to this new rooting method, but I thought I should still mention it for those of you still holding on to a 220.127.116.11 or older Fire TV.