Is it possible to update libc6 on the ubuntu or debian image to v2.23?
Don’t know if you are still interested in this but, yes, its possible but, no, its not recommended!
The “normal” debian image we release is based on the stable (jessie) release and that has a fixed version of glibc. To get a new one you need to upgrade to testing or (probably better) unstable.
Given glibc has fairly strong back compatibility guarantees the safest thing to so might to persuade apt to grab glibc from unstable and other packages from jessie. Take a look at Debian APT manual for some hints on how to do that!