CVE-2023-46836

Summary

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 Software

Weaknesses

Workarounds

Running only HVM or PVH VMs will avoid the vulnerability.

ADP Enrichment

CVE Program Container

Additional References

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

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: no
  • Technical Impact: partial

References

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

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