An out-of-bounds memory access in the generateDirectionalRuns() function in qtextengine.cpp in Qt qtbase 5.11.x and 5.12.x before 5.12.5 allows attackers to cause a denial of service by crashing an application via a text file containing many directional characters.
https://www.debian.org/security/2019/dsa-4556
https://usn.ubuntu.com/4275-1/
https://security.gentoo.org/glsa/202003-60
https://seclists.org/bugtraq/2019/Nov/4
https://codereview.qt-project.org/c/qt/qtbase/+/271889
https://bugs.launchpad.net/ubuntu/+source/qtbase-opensource-src/+bug/1848784