CVE-2019-18421

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Summary

CVECVE-2019-18421
StatePUBLIC
Assigner[email protected]
Source PriorityCVE Program / NVD first with legacy fallback
Published2019-10-31 14:15:00 UTC
Updated2023-11-07 03:06:00 UTC
DescriptionAn issue was discovered in Xen through 4.12.x allowing x86 PV guest OS users to gain host OS privileges by leveraging race conditions in pagetable promotion and demotion operations. There are issues with restartable PV type change operations. To avoid using shadow pagetables for PV guests, Xen exposes the actual hardware pagetables to the guest. In order to prevent the guest from modifying these page tables directly, Xen keeps track of how pages are used using a type system; pages must be "promoted" before being used as a pagetable, and "demoted" before being used for any other type. Xen also allows for "recursive" promotions: i.e., an operating system promoting a page to an L4 pagetable may end up causing pages to be promoted to L3s, which may in turn cause pages to be promoted to L2s, and so on. These operations may take an arbitrarily large amount of time, and so must be re-startable. Unfortunately, making recursive pagetable promotion and demotion operations restartable is incredibly complicated, and the code contains several races which, if triggered, can cause Xen to drop or retain extra type counts, potentially allowing guests to get write access to in-use pagetables. A malicious PV guest administrator may be able to escalate their privilege to that of the host. All x86 systems with untrusted PV guests are vulnerable. HVM and PVH guests cannot exercise this vulnerability.

Risk And Classification

Problem Types: CWE-362

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Debian Debian Linux 10.0 All All All
Operating System Debian Debian Linux 9.0 All All All
Operating System Fedoraproject Fedora 29 All All All
Operating System Fedoraproject Fedora 30 All All All
Operating System Fedoraproject Fedora 31 All All All
Operating System Opensuse Leap 15.0 All All All
Operating System Xen Xen All All All All

References

ReferenceSourceLinkTags
Debian -- Security Information -- DSA-4602-1 xen DEBIAN www.debian.org
Xen: Multiple vulnerabilities (GLSA 202003-56) — Gentoo security GENTOO security.gentoo.org
[SECURITY] Fedora 30 Update: xen-4.11.2-3.fc30 - package-announce - Fedora Mailing-Lists lists.fedoraproject.org
[SECURITY] Fedora 29 Update: xen-4.11.2-2.fc29 - package-announce - Fedora Mailing-Lists lists.fedoraproject.org
[SECURITY] Fedora 29 Update: xen-4.11.2-2.fc29 - package-announce - Fedora Mailing-Lists FEDORA lists.fedoraproject.org
XSA-299 - Xen Security Advisories MISC xenbits.xen.org Patch, Vendor Advisory
Bugtraq: [SECURITY] [DSA 4602-1] xen security update BUGTRAQ seclists.org
[security-announce] openSUSE-SU-2019:2506-1: important: Security update SUSE lists.opensuse.org
oss-security - Xen Security Advisory 299 v4 (CVE-2019-18421) - Issues with restartable PV type change operations MLIST www.openwall.com Mailing List, Patch, Third Party Advisory
[SECURITY] Fedora 31 Update: xen-4.12.1-6.fc31 - package-announce - Fedora Mailing-Lists FEDORA lists.fedoraproject.org
[SECURITY] Fedora 31 Update: xen-4.12.1-6.fc31 - package-announce - Fedora Mailing-Lists lists.fedoraproject.org
[SECURITY] Fedora 30 Update: xen-4.11.2-3.fc30 - package-announce - Fedora Mailing-Lists FEDORA lists.fedoraproject.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Legacy QID Mappings

  • 500754 Alpine Linux Security Update for xen
  • 504531 Alpine Linux Security Update for xen
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