The spectre_v2_select_mitigation function in arch/x86/kernel/cpu/bugs.c in the Linux kernel before 4.18.1 does not always fill RSB upon a context switch, which makes it easier for attackers to conduct userspace-userspace spectreRSB attacks.
4.4.0-1031.344.15.0-1030.31~14.04.14.4.0-137.163~14.04.14.4.0-137.1634.4.0-1069.794.15.0-1025.26~16.04.14.15.0-1021.22~16.04.14.15.0-36.39~16.04.14.4.0-1035.414.4.0-1098.106Exploitability
AV:LAC:LPR:LUI:NScope
S:CImpact
C:HI:NA:NCVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N