What’s Vulnerable › Vulnerabilities

CVE-2026-79611: VMX: VMentry failure with branch tracing and blocked states

• Severity: medium (CVSS 5.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-13 · updated 2026-10-20
• Weakness: CWE-843

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.

References

• https://xenbits.xenproject.org/xsa/advisory-518.html
• http://www.openwall.com/lists/oss-security/2026/10/13/7
• http://xenbits.xen.org/xsa/advisory-518.html

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