Xen out of bounds event channels available to 32-bit x86 domains DoS (XSA-342)

medium Nessus Plugin ID 144784
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Synopsis

The remote Xen hypervisor installation is missing a security update.

Description

A denial of service (DoS) vulnerability exists in Xen servers on a 32-bit x86 domains out of bounds event channels due to improper restrictions on limits on the number of usable event channels. The so called 2-level event channel model imposes different limits on the number of usable event channels for 32-bit x86 domains vs 64-bit or Arm (either bitness) ones. 32-bit x86 domains can use only 1023 channels, due to limited space in their shared (between guest and Xen) information structure, whereas all other domains can use up to 4095 in this model. The recording of the respective limit during domain initialization, however, has occurred at a time where domains are still deemed to be 64-bit ones, prior to actually honoring respective domain properties. At the point domains get recognized as 32-bit ones, the limit didn't get updated accordingly. Due to this misbehavior in Xen, 32-bit domains (including Domain 0) servicing other domains may observe event channel allocations to succeed when they should really fail. Subsequent use of such event channels would then possibly lead to corruption of other parts of the shared info structure. An unprivileged guest may cause another domain, in particular Domain 0, to misbehave. This may lead to a Denial of Service (DoS) for the entire system.

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

https://xenbits.xen.org/xsa/advisory-342.html

Plugin Details

Severity: Medium

ID: 144784

File Name: xen_server_XSA-342.nasl

Version: 1.3

Type: local

Family: Misc.

Published: 1/7/2021

Updated: 6/3/2021

Dependencies: xen_server_detect.nbin

Configuration: Enable paranoid mode

Risk Information

CVSS Score Source: CVE-2020-25600

VPR

Risk Factor: Medium

Score: 4.4

CVSS v2

Risk Factor: Medium

Base Score: 4.9

Temporal Score: 3.6

Vector: AV:L/AC:L/Au:N/C:N/I:N/A:C

Temporal Vector: E:U/RL:OF/RC:C

CVSS v3

Risk Factor: Medium

Base Score: 5.5

Temporal Score: 4.8

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Temporal Vector: E:U/RL:O/RC:C

Vulnerability Information

CPE: cpe:/o:xen:xen

Required KB Items: installed_sw/Xen Hypervisor, Settings/ParanoidReport

Exploit Ease: No known exploits are available

Patch Publication Date: 9/22/2020

Vulnerability Publication Date: 9/22/2020

Reference Information

CVE: CVE-2020-25600

IAVB: 2020-B-0056-S

CWE: 119