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Vulnerability Details : CVE-2019-18421

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.
Publish Date : 2019-10-31 Last Update Date : 2019-11-14
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- CVSS Scores & Vulnerability Types

CVSS Score
7.1
Confidentiality Impact Complete (There is total information disclosure, resulting in all system files being revealed.)
Integrity Impact Complete (There is a total compromise of system integrity. There is a complete loss of system protection, resulting in the entire system being compromised.)
Availability Impact Complete (There is a total shutdown of the affected resource. The attacker can render the resource completely unavailable.)
Access Complexity High (Specialized access conditions exist. It is hard to exploit and several special conditions must be satisfied to exploit)
Authentication ???
Gained Access None
Vulnerability Type(s) Gain privileges
CWE ID 362

- Products Affected By CVE-2019-18421

# Product Type Vendor Product Version Update Edition Language
1 OS XEN XEN * * * * Version Details Vulnerabilities

- Number Of Affected Versions By Product

Vendor Product Vulnerable Versions
XEN XEN 1

- References For CVE-2019-18421

https://seclists.org/bugtraq/2020/Jan/21
BUGTRAQ 20200114 [SECURITY] [DSA 4602-1] xen security update
https://www.debian.org/security/2020/dsa-4602
DEBIAN DSA-4602
https://lists.fedoraproject.org/archives/list/[email protected]/message/IZYATWNUGHRBG6I3TC24YHP5Y3J7I6KH/
FEDORA FEDORA-2019-cbb732f760
https://lists.fedoraproject.org/archives/list/[email protected]/message/I5WWPW4BSZDDW7VHU427XTVXV7ROOFFW/
FEDORA FEDORA-2019-376ec5c107
https://lists.fedoraproject.org/archives/list/[email protected]/message/2BQKX7M2RHCWDBKNPX4KEBI3MJIH6AYZ/
FEDORA FEDORA-2019-865bb16900
http://lists.opensuse.org/opensuse-security-announce/2019-11/msg00037.html
SUSE openSUSE-SU-2019:2506
http://www.openwall.com/lists/oss-security/2019/10/31/3
MLIST [oss-security] 20191031 Xen Security Advisory 299 v4 (CVE-2019-18421) - Issues with restartable PV type change operations
http://xenbits.xen.org/xsa/advisory-299.html
https://security.gentoo.org/glsa/202003-56
GENTOO GLSA-202003-56

- Metasploit Modules Related To CVE-2019-18421

There are not any metasploit modules related to this CVE entry (Please visit www.metasploit.com for more information)


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