Fossil before 2.10.2, 2.11.x before 2.11.2, and 2.12.x before 2.12.1 allows remote authenticated users to execute arbitrary code. An attacker must have check-in privileges on the repository.
https://www.openwall.com/lists/oss-security/2020/08/20/1
https://security.gentoo.org/glsa/202011-04
https://fossil-scm.org/fossil/vdiff?branch=sec2020-2.12-patch&diff=1&w
https://fossil-scm.org/forum/info/a05ae3ce7760daf6
http://www.openwall.com/lists/oss-security/2020/08/25/1
http://lists.opensuse.org/opensuse-security-announce/2020-09/msg00065.html