The agroot() function in cgraph\obj.c in libcgraph.a in Graphviz 2.39.20160612.1140 has a NULL pointer dereference, as demonstrated by graphml2gv.
lists.opensuse.org/opensuse-security-announce/2019-05/msg00054.html
lists.opensuse.org/opensuse-security-announce/2019-05/msg00065.html
lists.opensuse.org/opensuse-security-announce/2020-06/msg00056.html
lists.opensuse.org/opensuse-security-announce/2020-06/msg00065.html
gitlab.com/graphviz/graphviz/issues/1517
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research.loginsoft.com/bugs/null-pointer-dereference-in-function-agroot/