CVE-2020-29487 Information

Description

An issue was discovered in Xen XAPI before 2020-12-15. Certain xenstore keys provide feedback from the guest and are therefore watched by toolstack. Specifically keys are watched by xenopsd and data are forwarded via RPC through message-switch to xapi. The watching logic in xenopsd sends one RPC update containing all data any time any single xenstore key is updated and therefore has O(N^2) time complexity. Furthermore message-switch retains recent (currently 128) RPC messages for diagnostic purposes yielding O(MN) space complexity. The quantity of memory a single guest can monopolise is bounded by xenstored quota but the quota is fairly large. It is believed to be in excess of 1G per malicious guest. In practice this manifests as a host denial of service either through message-switch thrashing against swap or OOMing entirely depending on dom0’s configuration. (There are no quotas in xenopsd to limit the quantity of keys that result in RPC traffic.) A buggy or malicious guest can cause unreasonable memory usage in dom0 resulting in a host denial of service. All versions of XAPI are vulnerable. Systems that are not using the XAPI toolstack are not vulnerable.

CVSS Vector

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

Reference

https://xenbits.xenproject.org/xsa/advisory-354.html https://security.gentoo.org/glsa/202107-30

Attack Complexity

LOW

Privileges Required

NONE

User Interaction Required

NONE

Scope

NONE

Confidentiality Impact

UNCHANGED

Integrity Impact

NONE

Availability Impact

NONE

Base Score

HIGH

Base Severity

7.5