xorg-x11-server before 1.19.5 was missing length validation in XFree86 DGA extension allowing malicious X client to cause X server to crash or possibly execute arbitrary code.
https://www.debian.org/security/2017/dsa-4000
https://security.gentoo.org/glsa/201711-05
https://cgit.freedesktop.org/xorg/xserver/commit/?id=1b1d4c04695dced2463404174b50b3581dbd857b