CVE-2023-46836

x86: BTC/SRSO fixes not fully effective

Published Jan 5, 2024 CVSS 3.1 · 4.7 Medium EPSS < 1% KEV · Not listed
Description
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.

Remediation

Vendor Workaround

Running only HVM or PVH VMs will avoid the vulnerability.

Tracking

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Advisories

Source ID Title
EUVD EUVD EUVD-2023-51002 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.
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
XEN
Published
Updated
Nov 4, 2025, 7:25 PM
Reserved
Oct 27, 2023, 7:55 AM
Status
Modified
Published
Jan 5, 2024, 5:15 PM
Modified
Jun 17, 2026, 6:31 AM