Vulnerability · Published Oct 13, 2026 · Assigned by XEN
CVE-2026-79611VMX: VMentry failure with branch tracing and blocked states
Medium 5.5
In plain English
A medium-severity type confusion in Xen from Xen. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 5% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
For XSA-308 logic was introduced, as VMX VMEntry checks do not like the exact combination of state which occurs when #DB in intercepted, Single Stepping is active, and blocked by STI/MovSS is active, despite this being a legitimate state to be in. The resulting VMEntry failure is fatal to the guest. Sadly there is another special sub-case of the above, with branch tracing enabled. In that case the prior adjustment would still cause a VMentry failure, as before fatal to the guest.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.21 | xen | 4.19.6-r2 | ALPINE-CVE-2026-79611 |
| Alpine:v3.22 | xen | 4.20.4-r2 | ALPINE-CVE-2026-79611 |
| Alpine:v3.23 | xen | 4.20.4-r2 | ALPINE-CVE-2026-79611 |
| Alpine:v3.24 | xen | 4.21.2-r2 | ALPINE-CVE-2026-79611 |
| Debian:12 | xen | 4.17.7+13-g2445b30a44-0+deb12u1 | DEBIAN-CVE-2026-79611 |
| Debian:13 | xen | 4.20.4+39-gf1e1321c87-0+deb13u1 | DEBIAN-CVE-2026-79611 |
| Debian:14 | xen | 4.20.4+39-gf1e1321c87-1 | DEBIAN-CVE-2026-79611 |
| Ubuntu:22.04:LTS | xen | no fix listed | UBUNTU-CVE-2026-79611 |
| Ubuntu:24.04:LTS | xen | no fix listed | UBUNTU-CVE-2026-79611 |
| Ubuntu:26.04:LTS | xen | no fix listed | UBUNTU-CVE-2026-79611 |
| Ubuntu:26.10 | xen | no fix listed | UBUNTU-CVE-2026-79611 |
Affected products (as reported)
Weakness: CWE-843 · Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H