A gdm bugfix update has been been released for CentOS 7.

CentOS-announce: CEBA-2020:5154 CentOS 7 gdm BugFix Update

CentOS Errata and Bugfix Advisory 2020:5154

Upstream details at :   https://access.redhat.com/errata/RHBA-2020:5154

The following updated files have been uploaded and are currently
syncing to the mirrors: ( sha256sum Filename )

x86_64:
aa4d5c25ee0ab0c6200041d7babcc2186123b17af2126662b27bed0013787faa gdm-3.28.2-26.el7.i686.rpm
d9df089dfd6da09a0d335f5f7217eb49fb786af4bc6bdc86f8f5780e9588cb54 gdm-3.28.2-26.el7.x86_64.rpm
b3523f6bd479abca1bc4c70f870af2423e9747ad2cb185692334588138742f50 gdm-devel-3.28.2-26.el7.i686.rpm
9a97f6e2d20a2e98ad20844706c47bf2fc689c6975c67067aa46d4ab03c1e47a gdm-devel-3.28.2-26.el7.x86_64.rpm
570aef75009a72d1f785eeeb0cf1e9b1c5113c73c46a3a7c2eebe0f87a44655b gdm-pam-extensions-devel-3.28.2-26.el7.i686.rpm
9b205c9658e9caf5ecd6d928179b7e7b36aa629b18e33540805f21a0d0b9f939 gdm-pam-extensions-devel-3.28.2-26.el7.x86_64.rpm

Source:
7299b27241d70ab051693e3987cc595e044eb8061493cd6809befd2e25892119 gdm-3.28.2-26.el7.src.rpm