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Fencer Vulns
medium 5.5

CVE-2026-79611 json

VMX: VMentry failure with branch tracing and blocked states

published 2026-10-13 26 d ago modified 2026-10-20 19 d ago also EUVD-2026-98828

cvss
5.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 5%
public exploits
0
none known

Summary

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.

Patch / fix

  • xen Debian 12 4.17.7+13-g2445b30a44-0+deb12u1
  • xen Debian 13 4.20.4+39-gf1e1321c87-0+deb13u1
  • xen Debian 14 4.20.4+39-gf1e1321c87-1

debian advisories DEBIAN-CVE-2026-79611

  • xen SLE Module for Server Applications 15 SP7, SLE Module for Basesystem 15 SP7 4.20.4_06-150700.3.49.2
  • xen SLES for SAP 15 SP4, SLES 15 SP4-LTSS, SLE Micro 5.4 +3 more 4.16.7_16-150400.4.95.1
  • xen SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 4.17.7_02-150500.3.82.1
  • xen SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 4.12.4_76-3.154.1

suse advisories SUSE-SU-2026:4942-1SUSE-SU-2026:4732-1SUSE-SU-2026:4642-1SUSE-SU-2026:4641-1

  • xen openSUSE Tumbleweed 4.22.0_06-1.1

opensuse advisories openSUSE-SU-2026:12138-1

  • xen Alpine 3.21 4.19.6-r2
  • xen Alpine 3.23, Alpine 3.22 4.20.4-r2
  • xen Alpine 3.24 4.21.2-r2

alpine advisories ALPINE-CVE-2026-79611

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-79611 updated cvss 5.5

xen: xen: Denial of Service of guest virtual machines via VM entry failure

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
19 d ago

Exploit prediction

0.16% chance of exploitation in the next 30 days, higher than 5% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CNA 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Xen Xen

Classification

Weakness
  • CWE-843 Access of Resource Using Incompatible Type

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.