x86: BTC/SRSO fixes not fully effective
CVE-2023-46836

4.7MEDIUM

Key Information:

Vendor

Xen Project
Status
Xen
Vendor
CVE Published:
5 January 2024

What is CVE-2023-46836?

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.

Affected Version(s)

Xen consult Xen advisory XSA-446

References

https://xenbits.xenproject.org/xsa/advisory-446.html

CVSS V3.1

Score:
4.7
Severity:
MEDIUM
Confidentiality:
High
Integrity:
None
Availability:
High
Attack Vector:
Local
Attack Complexity:
High
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

This issue was discovered by Andrew Cooper of XenServer.
.