A flaw was found in xorg-x11-server before 1.20.9. An integer underflow in the X input extension protocol decoding in the X server may lead to arbitrary access of memory contents. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.
https://bugzilla.redhat.com/show_bug.cgi?id=1862246
https://security.gentoo.org/glsa/202012-01