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Cve@mitre.orgCVE-2019-18421
HistoryOct 31, 2019 - 2:15 p.m.

CVE-2019-18421

2019-10-3114:15:00
CWE-362
cve@mitre.org
web.nvd.nist.gov
128
xen
cve-2019-18421
security vulnerability
x86
pv guest
host os privileges
race conditions
pagetable promotion

7.5 High

CVSS3

Attack Vector

NETWORK

Attack Complexity

HIGH

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

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

7.5 High

AI Score

Confidence

Low

7.1 High

CVSS2

Access Vector

NETWORK

Access Complexity

HIGH

Authentication

SINGLE

Confidentiality Impact

COMPLETE

Integrity Impact

COMPLETE

Availability Impact

COMPLETE

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

0.004 Low

EPSS

Percentile

73.9%

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.

Use Vulners API to create your own security tool

API usage cases
  • Network scanning
  • Linux Patch management
  • Threat protection
  • No network audit solution

Ways of integration

Integrate Vulners API

7.5 High

CVSS3

Attack Vector

NETWORK

Attack Complexity

HIGH

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

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

7.5 High

AI Score

Confidence

Low

7.1 High

CVSS2

Access Vector

NETWORK

Access Complexity

HIGH

Authentication

SINGLE

Confidentiality Impact

COMPLETE

Integrity Impact

COMPLETE

Availability Impact

COMPLETE

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

0.004 Low

EPSS

Percentile

73.9%

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