CVE-2020-11739

Description

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.

How to fix CVE-2020-11739

To remediate CVE-2020-11739, upgrade the affected package to a fixed version below.

• —upgrade to 4.12.2-r1 or later
• —upgrade to 4.11.4-1 or later
• —upgrade to 4.11.4+24-gddaaccbbab-1~deb10u1 or later

Is CVE-2020-11739 being exploited?

Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.

Affected packages (3)

• from 0, < 4.12.2-r1
• from 0, < 4.11.4-1
• from 0, < 4.11.4+24-gddaaccbbab-1~deb10u1

CVSS scores

References (2)

• ADVISORYsecurity.alpinelinux.org/vuln/CVE-2020-11739
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2020-11739