An issue was discovered in Xen through 4.14.x. Some OSes (such as Linux, FreeBSD, and NetBSD) are processing watch events using a single thread. If the events are received faster than the thread is able to handle, they will get queued. As the queue is unbounded, a guest may be able to trigger an OOM in the backend. All systems with a FreeBSD, Linux, or NetBSD (any version) dom0 are vulnerable.
https://xenbits.xenproject.org/xsa/advisory-349.html
https://www.debian.org/security/2021/dsa-4843
https://lists.debian.org/debian-lts-announce/2021/02/msg00018.html
https://lists.debian.org/debian-lts-announce/2021/03/msg00010.html
Source: MITRE
Published: 2020-12-15
Updated: 2022-04-26
Type: CWE-770
Base Score: 4.9
Vector: AV:L/AC:L/Au:N/C:N/I:N/A:C
Impact Score: 6.9
Exploitability Score: 3.9
Severity: MEDIUM
Base Score: 6.5
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
Impact Score: 4
Exploitability Score: 2
Severity: MEDIUM