high
8.8
CWE
400
Advisory Published
Updated

CVE-2020-15565

First published: Tue Jul 07 2020(Updated: )

An issue was discovered in Xen through 4.13.x, allowing x86 Intel HVM guest OS users to cause a host OS denial of service or possibly gain privileges because of insufficient cache write-back under VT-d. When page tables are shared between IOMMU and CPU, changes to them require flushing of both TLBs. Furthermore, IOMMUs may be non-coherent, and hence prior to flushing IOMMU TLBs, a CPU cache also needs writing back to memory after changes were made. Such writing back of cached data was missing in particular when splitting large page mappings into smaller granularity ones. A malicious guest may be able to retain read/write DMA access to frames returned to Xen's free pool, and later reused for another purpose. Host crashes (leading to a Denial of Service) and privilege escalation cannot be ruled out. Xen versions from at least 3.2 onwards are affected. Only x86 Intel systems are affected. x86 AMD as well as Arm systems are not affected. Only x86 HVM guests using hardware assisted paging (HAP), having a passed through PCI device assigned, and having page table sharing enabled can leverage the vulnerability. Note that page table sharing will be enabled (by default) only if Xen considers IOMMU and CPU large page size support compatible.

Credit: cve@mitre.org cve@mitre.org

Affected SoftwareAffected VersionHow to fix
Xen Xen>=3.2.0<=4.13.1
Debian Debian Linux=10.0
Fedoraproject Fedora=31
Fedoraproject Fedora=32
openSUSE Leap=15.1
openSUSE Leap=15.2
debian/xen
4.14.6-1
4.14.5+94-ge49571868d-1
4.17.3+10-g091466ba55-1~deb12u1
4.17.3+36-g54dacb5c02-1

Remedy

http://xenbits.xen.org/xsa/advisory-321.html

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Reference Links

Frequently Asked Questions

  • What is the vulnerability ID?

    The vulnerability ID is CVE-2020-15565.

  • What is the affected software?

    The affected software is Xen versions through 4.13.x.

  • How can x86 Intel HVM guest OS users exploit this vulnerability?

    x86 Intel HVM guest OS users can exploit this vulnerability to cause a denial of service on the host OS or potentially gain privileges due to insufficient cache write-back under VT-d.

  • How can this vulnerability be fixed for Ubuntu users?

    Ubuntu users can fix this vulnerability by updating Xen to version 4.11.3+24- or later.

  • How can this vulnerability be fixed for Debian users?

    Debian users can fix this vulnerability by updating Xen to version 4.11.4+107-gef32c7afa2-1, 4.14.5+94-ge49571868d-1, 4.17.1+2-gb773c48e36-1, or 4.17.2-1.

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