CVE-2020-25602
Description
A flaw was found in Xen, specifically when a guest accesses certain Model Specific Registers where Xen first reads the value from hardware to use as the basis for auditing the guest access. For the MISC_ENABLE MSR, an Intel specific MSR, this MSR read is performed without error handling for a #GP fault, which is the consequence of trying to read this MSR on non-Intel hardware. This flaw allows an unprivileged guest to crash Xen, leading to a denial of service (DoS) for the entire system. The highest threat from this vulnerability is to system availability.
Statement
Only x86 systems which do not implement the MISC_ENABLE MSR (0x1a0) are vulnerable and only Xen versions 4.11 and onwards are vulnerable. Red Hat Enterprise Linux 5 is not affected by this flaw, as it shipped an older version of Xen.
Mitigation
Running only HVM/PVH guests avoids the vulnerability.
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 | 6.5 | 6 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | Low | High | N/A |
| User Interaction | None | None | N/A |
| Scope | Changed | Changed | N/A |
| Confidentiality | None | None | N/A |
| Integrity Impact | None | None | 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:N/I:N/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:N/I:N/A:H
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
Acknowledgements
Red Hat would like to thank the Xen project for reporting this issue.
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