The EVTCHNOP_expand_array hypercall checks for whether FIFO event channels are enabled, but without holding the correct lock. It can race with EVTCHNOP_reset, resulting in dereferencing a NULL pointer.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:LI:LA:L7.3/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L