CVE-2020-11739

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.

• CVE ID
• CVE-2020-11739

• Assigner
• cve@mitre.org

• Vulnerability Status
• Analyzed

• Published Version
• 2020-04-14T13:15:12

• Last Modified Date
• 2022-05-03T14:05:13

• Version
• 2.0

• Vector String
• AV:L/AC:M/Au:N/C:C/I:C/A:C

• Access Vector
• LOCAL

• Access Compatibility
• MEDIUM

• Authentication
• NONE

• Confidentiality Impact
• COMPLETE

• Integrity Impact
• COMPLETE

• Availability Impact
• COMPLETE

• Base Score
• 6.9

• Severity
• MEDIUM

• Exploitability Score
• 3.4

• Impact Score
• 10

• Version
• 3.1

• Vector String
• CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H

• Attack Vector
• LOCAL

• Attack Compatibility
• HIGH

• Privileges Required
• LOW

• User Interaction
• NONE

• Scope
• CHANGED

• Confidentiality Impact
• HIGH

• Availability Impact
• HIGH

• Base Score
• 7.8

• Base Severity
• HIGH

• Exploitability Score
• 1.1

• Impact Score
• 6