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CVE-2026-23553

CVE-2026-23553 · x86: incomplete IBPB for vCPU isolation

This page contains facts from public vulnerability sources. Check the original advisory before updating.

In the context switch logic Xen attempts to skip an IBPB in the case of a vCPU returning to a CPU on which it was the previous vCPU to run. While safe for Xen's isolation between vCPUs, this prevents the guest kernel correctly isolating between tasks. Consider: 1) vCPU runs on CPU A, running task 1. 2) vCPU moves to CPU B, idle gets scheduled on A. Xen skips IBPB. 3) On CPU B, guest kernel switches from task 1 to 2, issuing IBPB. 4) vCPU moves back to CPU A. Xen skips IBPB again. Now, task 2 is running on CPU A with task 1's training still in the BTB.

CVSS 2.9 · Low · EPSS 0.1% · Fix available

Published
Updated

Stack: system

Affected products and versions

  • xen

    Versions
    • consult Xen advisory XSA-479: Unknown

    No fix published

  • xen Debian:12

    Versions
    • 4.17.1+2-gb773c48e36-1
    • 4.17.2+55-g0b56bed864-1
    • 4.17.2+76-ge1f9cb16e2-1
    • 4.17.2+76-ge1f9cb16e2-1~deb12u1
    • 4.17.2-1
    • 4.17.3+10-g091466ba55-1
    • 4.17.3+10-g091466ba55-1.1
    • 4.17.3+10-g091466ba55-1.1~exp1
    • 4.17.3+10-g091466ba55-1.1~exp2
    • 4.17.3+10-g091466ba55-1~deb12u1
    • 4.17.3+36-g54dacb5c02-1
    • 4.17.5+23-ga4e5191dc0-1
    • 4.17.5+23-ga4e5191dc0-1+deb12u1
    • 4.17.5+72-g01140da4e8-1
    Affected ranges
    • ECOSYSTEM: < 4.17.7-0+deb12u1

    Update to 4.17.7-0+deb12u1

  • xen Debian:13

    Versions
    • 4.20.0+68-g35cb38b222-1
    • 4.20.2+7-g1badcf5035-0+deb13u1
    • 4.20.2+7-g1badcf5035-1
    • 4.20.2+7-g1badcf5035-2
    Affected ranges
    • ECOSYSTEM: < 4.20.2+37-g61ff35323e-0+deb13u1

    Update to 4.20.2+37-g61ff35323e-0+deb13u1

  • xen Debian:14

    Versions
    • 4.20.0+68-g35cb38b222-1
    • 4.20.2+7-g1badcf5035-1
    • 4.20.2+7-g1badcf5035-2
    Affected ranges
    • ECOSYSTEM: < 4.20.2+37-g61ff35323e-1

    Update to 4.20.2+37-g61ff35323e-1

  • xen Ubuntu:16.04:LTS

    Versions
    • 4.5.1-0ubuntu1
    • 4.5.1-0ubuntu2
    • 4.6.0-1ubuntu1
    • 4.6.0-1ubuntu2
    • 4.6.0-1ubuntu4
    • 4.6.0-1ubuntu4.1
    • 4.6.0-1ubuntu4.2
    • 4.6.0-1ubuntu4.3
    • 4.6.5-0ubuntu1
    • 4.6.5-0ubuntu1.1
    • 4.6.5-0ubuntu1.2
    • 4.6.5-0ubuntu1.4
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • xen Ubuntu:18.04:LTS

    Versions
    • 4.9.0-0ubuntu3
    • 4.9.0-0ubuntu4
    • 4.9.2-0ubuntu1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • xen Ubuntu:20.04:LTS

    Versions
    • 4.9.2-0ubuntu2
    • 4.9.2-0ubuntu6
    • 4.9.2-0ubuntu7
    • 4.11.3+24-g14b62ab3e5-1ubuntu1
    • 4.11.3+24-g14b62ab3e5-1ubuntu2
    • 4.11.3+24-g14b62ab3e5-1ubuntu2.2
    • 4.11.3+24-g14b62ab3e5-1ubuntu2.3
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • xen Ubuntu:22.04:LTS

    Versions
    • 4.11.4+24-gddaaccbbab-1ubuntu2
    • 4.16.0-1~ubuntu2
    • 4.16.0-1~ubuntu2.1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • xen Ubuntu:24.04:LTS

    Versions
    • 4.17.2-1
    • 4.17.2+55-g0b56bed864-1
    • 4.17.2+76-ge1f9cb16e2-1
    • 4.17.2+76-ge1f9cb16e2-1ubuntu1
    • 4.17.3+10-g091466ba55-1
    • 4.17.3+10-g091466ba55-1.1ubuntu2
    • 4.17.3+10-g091466ba55-1.1ubuntu3
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • xen Ubuntu:25.10

    Versions
    • 4.20.0-1ubuntu1
    • 4.20.0+68-g35cb38b222-1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • xen Ubuntu:26.10

    Versions
    • 4.20.2+7-g1badcf5035-2build2
    • 4.20.2+37-g61ff35323e-1ubuntu1
    • 4.20.3+127-gc42374a105-1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • xen Ubuntu:26.04:LTS

    Versions
    • 4.20.0+68-g35cb38b222-1
    • 4.20.2+7-g1badcf5035-2
    • 4.20.2+7-g1badcf5035-2build2
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

Original sources

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