CVE-2020-11739: Debian Linux

High severity, CVSS 7.8. EPSS: 0.3% chance of exploitation in the next 30 days.

An issue was discovered in Xen through 4.13.x, allowing guest OS users to cause a denial of service or possibly gain privileges because of missing memory barriers in read-write unlock paths. The read-write unlock paths don't contain a memory barrier. On Arm, this means a processor is allowed to re-order the memory access with the preceding ones. In other words, the unlock may be seen by another processor before all the memory accesses within the "critical" section. As a consequence, it may be possible to have a writer executing a critical section at the same time as readers or another writer. In other words, many of the assumptions (e.g., a variable cannot be modified after a check) in the critical sections are not safe anymore. The read-write locks are used in hypercalls (such as grant-table ones), so a malicious guest could exploit the race. For instance, there is a small window where Xen can leak memory if XENMAPSPACE_grant_table is used concurrently. A malicious guest may be able to leak memory, or cause a hypervisor crash resulting in a Denial of Service (DoS). Information leak and privilege escalation cannot be excluded.

Affected products

• Debian Debian Linux: version 10.0 only
• Fedoraproject Fedora: version 30 only; version 31 only; version 32 only
• Opensuse Leap: version 15.1 only
• Xen Xen: up to and including 4.13.0; version 4.13.0 only

Published 2020-04-14. Last modified 2026-06-17.