# CVE-2023-46836: xen: The fixes for XSA-422 (Branch Type Confusion) and XSA-434 (Speculative Return Stack Overflow) are not IRQ-safe

CVE-2023-46836 is fixed in xen on 1 platform, first by DEBIAN-CVE-2023-46836, released January 5, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2023-46836
- Priority: Routine
- CVSS: 4.7 (medium)
- EPSS: 0.0025
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jan 5, 2024

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | xen Debian 12.15 (bookworm) | 4.17.2+76-ge1f9cb16e2-1~deb12u1 | [DEBIAN-CVE-2023-46836](https://patchblox.com/security/data/fix/linux/debian-cve-2023-46836.md) | Jan 5, 2024 |
| Linux | xen Debian 13.5 (trixie) | 4.17.2+76-ge1f9cb16e2-1 | [DEBIAN-CVE-2023-46836](https://patchblox.com/security/data/fix/linux/debian-cve-2023-46836.md) | Jan 5, 2024 |
| Linux | xen Debian 14 | 4.17.2+76-ge1f9cb16e2-1 | [DEBIAN-CVE-2023-46836](https://patchblox.com/security/data/fix/linux/debian-cve-2023-46836.md) | Jan 5, 2024 |

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