The fixes for XSA-422 (Branch Type Confusion) and XSA-434 (Speculative Return Stack Overflow) are not IRQ-safe. It was believed that the mitigations always operated in contexts with IRQs disabled. However, the original XSA-254 fix for Meltdown (XPTI) deliberately left interrupts enabled on two entry paths; one unconditionally, and one conditionally on whether XPTI was active. As BTC/SRSO and Meltdown affect different CPU vendors, the mitigations are not active together by default. Therefore, there is a race condition whereby a malicious PV guest can bypass BTC/SRSO protections and launch a BTC/SRSO attack against Xen.
NVD Severity
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Type URI

Match rules

CPE URI Source package Min version Max version
cpe:2.3:o:xen:xen:*:*:*:*:*:*:*:* xen == None == None

Vulnerable and fixed packages

Source package Branch Version Maintainer Status
xen 3.19-main 4.18.2-r0 Natanael Copa <> fixed
xen 3.18-main 4.17.4-r0 Natanael Copa <> fixed
xen 3.17-main 4.16.6-r0 Natanael Copa <> fixed
xen 3.16-main 4.16.6-r0 Natanael Copa <> fixed
xen 3.20-main 4.18.2-r1 Natanael Copa <> fixed
xen edge-main 4.18.2-r2 Natanael Copa <> fixed