Detections
Analytics
Xen Xenstore Use-After-Free DoS (XSA-325)
medium Nessus Plugin ID 149065
Language:
Synopsis
The remote Xen hypervisor installation is missing a security update.Description
According to its self-reported version number, the Xen hypervisor installed on the remote host is affected by an issue.Xenstored and guests communicate via a shared memory page using a specific protocol. When a guest violates this protocol, xenstored will drop the connection to that guest. Unfortunately, this is done by just removing the guest from xenstored's internal management, resulting in the same actions as if the guest had been destroyed, including sending an @releaseDomain event. @releaseDomain events do not say that the guest has been removed. All watchers of this event must look at the states of all guests to find the guest that has been removed. When an @releaseDomain is generated due to a domain xenstored protocol violation, because the guest is still running, the watchers will not react. Later, when the guest is actually destroyed, xenstored will no longer have it stored in its internal data base, so no further @releaseDomain event will be sent. This can lead to a zombie domain; memory mappings of that guest's memory will not be removed, due to the missing event. This zombie domain will be cleaned up only after another domain is destroyed, as that will trigger another @releaseDomain event. If the device model of the guest that violated the Xenstore protocol is running in a stub-domain, a use-after-free case could happen in xenstored, after having removed the guest from its internal data base, possibly resulting in a crash of xenstored. A malicious guest can block resources of the host for a period after its own death. Guests with a stub domain device model can eventually crash xenstored, resulting in a more serious denial of service (the prevention of any further domain management operations).
Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.
Solution
Apply the appropriate patch according to the vendor advisory.See Also
Plugin Details
Severity: Medium
ID: 149065
File Name: xen_server_XSA-325.nasl
Version: 1.2
Type: local
Family: Misc.
Published: 4/29/2021
Updated: 4/30/2021
Configuration: Enable paranoid mode
Supported Sensors: Nessus
Risk Information
VPR
Risk Factor: Medium
Score: 4.4
CVSS v2
Risk Factor: Medium
Base Score: 4.9
Temporal Score: 3.6
Vector: CVSS2#AV:L/AC:L/Au:N/C:N/I:N/A:C
CVSS Score Source: CVE-2020-29483
CVSS v3
Risk Factor: Medium
Base Score: 6.5
Temporal Score: 5.7
Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C
Vulnerability Information
CPE: cpe:/o:xen:xen
Required KB Items: Settings/ParanoidReport, installed_sw/Xen Hypervisor
Exploit Ease: No known exploits are available
Patch Publication Date: 12/15/2020
Vulnerability Publication Date: 12/15/2020
Reference Information
CVE: CVE-2020-29483