CVE-2020-15565
Description
A flaw was found in Xen, in the page table sharing between the IOMMU and CPU. This flaw allows a malicious guest user to access sensitive information pertaining to other guests to crash the host, resulting in a denial of service and privilege escalation. The highest threat from this vulnerability is to system availability.
Statement
Only x86 HVM guests using hardware assisted paging (HAP), having a passed through PCI device assigned, and having page table sharing enabled can leverage the vulnerability. Note that page table sharing is enabled (by default) only if Xen considers IOMMU and CPU large page size support compatible. x86 AMD as well as ARM systems are not affected by this flaw.
Mitigation
- Suppress the use of page table sharing (command line option `iommu=no-sharept`). Note however that as of Xen version 4.13 there is also a respective per-guest control (`passthrough=` libxl guest config file option). If any guests have been created with an explicit setting, this setting may conflict with the addition of the `iommu=no-sharept` Xen command line option.
- Suppress the use of large HAP pages (command line options `hap_2mb=no` and `hap_1gb=no`).
- Avoid pass-through of PCI devices to HVM guests.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.9 | 8.8 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | Low | Low | N/A |
| User Interaction | None | None | N/A |
| Scope | Changed | Changed | N/A |
| Confidentiality | Low | High | N/A |
| Integrity Impact | Low | High | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Application Data
Acknowledgements
Red Hat would like to thank the Xen project for reporting this issue.
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