Fedora 27 ships with version 2.26 of the GNU C Library (glibc). New features include:
A per-thread malloc cache has been added that significantly improves the malloc API family of functions on certain multithreaded workloads.
Unicode 10.0.0 support for character encodings, character type info, and transliteration tables.
Improvements in the DNS stub resolver including runtime detection of changed DNS servers (/etc/resolv.conf changes) and use of those new servers without needing to restart the process.
Security improvements include fixes for the following vulnerabilities: CVE-2017-12132, CVE-2017-1000366, CVE-2010-3192, CVE-2017-12133.
More information about this version of the GNU C Library can be found in the release notes.