GNU Bison before 3.5.4 allows attackers to cause a denial of service (application crash). NOTE: there is a risk only if Bison is used with untrusted input, and an observed bug happens to cause unsafe behavior with a specific compiler/architecture. The bug reports were intended to show that a crash may occur in Bison itself, not that a crash may occur in code that is generated by Bison.
https://lists.gnu.org/archive/html/info-gnu/2020-04/msg00000.html