CVE-2020-11739
xen: missing memory barriers in read-write unlock paths (XSA-314)
Published Apr 14, 2020
CVSS 3.1 · 7.8 High
EPSS < 1%
KEV · Not listed
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.
Affected Products
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CVE record
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NVD configurations
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Red Hat packages
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OpenCVE enrichment
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Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
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No data available yet.
Remediation
Tracking
Advisories
| Source | ID | Title |
|---|---|---|
 Debian DSA |
DSA-4723-1 | xen security update |
 EUVD |
EUVD-2020-4081 | 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. |
 Ubuntu USN |
USN-5617-1 | Xen vulnerabilities |
Metrics
No CVSS v4.0
Attack Vector Local
Attack Complexity High
Privileges Required Low
Scope Changed
Confidentiality Impact High
Integrity Impact High
Availability Impact High
User Interaction None
No CVSS v3.0
Access Vector Local
Access Complexity Medium
Authentication None
Confidentiality Impact Complete
Integrity Impact Complete
Availability Impact Complete
This CVE is not in the KEV list.
Exploit prediction score: < 1% (0.288% probability within 30 days)
Key SSVC decision points have not yet been added.
References
History
No history.
Subscriptions
Weaknesses
