CVE-2019-18421

high
New! CVE Severity Now Using CVSS v3

The calculated severity for CVEs has been updated to use CVSS v3 by default. CVEs that do not have a CVSS v3 score will fall back CVSS v2 for calculating severity. Severity display preferences can be toggled in the settings dropdown.

Description

An 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.

References

http://lists.opensuse.org/opensuse-security-announce/2019-11/msg00037.html

http://www.openwall.com/lists/oss-security/2019/10/31/3

http://xenbits.xen.org/xsa/advisory-299.html

https://lists.fedoraproject.org/archives/list/[email protected]/message/2BQKX7M2RHCWDBKNPX4KEBI3MJIH6AYZ/

https://lists.fedoraproject.org/archives/list/[email protected]/message/I5WWPW4BSZDDW7VHU427XTVXV7ROOFFW/

Details

Source: MITRE

Published: 2019-10-31

Updated: 2019-11-14

Type: CWE-362

Risk Information

CVSS v2

Base Score: 7.1

Vector: AV:N/AC:H/Au:S/C:C/I:C/A:C

Impact Score: 10

Exploitability Score: 3.9

Severity: HIGH

CVSS v3

Base Score: 7.5

Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

Impact Score: 5.9

Exploitability Score: 1.6

Severity: HIGH

Vulnerable Software

Configuration 1

OR

cpe:2.3:o:xen:xen:*:*:*:*:*:*:x86:* versions up to 4.12.1 (inclusive)

Tenable Plugins

View all (15 total)

IDNameProductFamilySeverity
150584SUSE SLES11 Security Update : xen (SUSE-SU-2020:14444-1)NessusSuSE Local Security Checks
critical
134964GLSA-202003-56 : Xen: Multiple vulnerabilities (MDSUM/RIDL) (MFBDS/RIDL/ZombieLoad) (MLPDS/RIDL) (MSBDS/Fallout)NessusGentoo Local Security Checks
critical
133763SUSE SLES12 Security Update : xen (SUSE-SU-2020:0388-1)NessusSuSE Local Security Checks
critical
133539SUSE SLES12 Security Update : xen (SUSE-SU-2020:0334-1)NessusSuSE Local Security Checks
critical
132875Debian DSA-4602-1 : xen - security update (MDSUM/RIDL) (MFBDS/RIDL/ZombieLoad) (MLPDS/RIDL) (MSBDS/Fallout)NessusDebian Local Security Checks
critical
132073SUSE SLES12 Security Update : xen (SUSE-SU-2019:3297-1)NessusSuSE Local Security Checks
critical
131460Fedora 30 : xen (2019-cbb732f760)NessusFedora Local Security Checks
critical
131143Fedora 31 : xen (2019-376ec5c107)NessusFedora Local Security Checks
critical
131133Xen Restartable PV Type Change Operations Elevation of Privilege Vulnerability (XSA-299)NessusMisc.
high
131098Fedora 29 : xen (2019-865bb16900)NessusFedora Local Security Checks
critical
131062openSUSE Security Update : xen (openSUSE-2019-2508)NessusSuSE Local Security Checks
critical
131060openSUSE Security Update : xen (openSUSE-2019-2506)NessusSuSE Local Security Checks
critical
130960SUSE SLED12 / SLES12 Security Update : xen (SUSE-SU-2019:2962-1)NessusSuSE Local Security Checks
critical
130959SUSE SLED15 / SLES15 Security Update : xen (SUSE-SU-2019:2961-1)NessusSuSE Local Security Checks
critical
130958SUSE SLED15 / SLES15 Security Update : xen (SUSE-SU-2019:2960-1)NessusSuSE Local Security Checks
critical