CVE-2020-25600
Description
A flaw was found in Xen. Misbehavior during domain initialization, where 32-bit domains (including Domain 0) servicing other domains, may observe event channel allocations to succeed when they should fail. Subsequent use of such event channels leads to the corruption of other parts of the shared information structure. This flaw allows an unprivileged guest to crash another domain, particularly Domain 0, leading to a denial of service (DoS) for the entire system. The highest threat from this vulnerability is to system availability.
Statement
All Xen versions from 4.4 onwards are vulnerable. Red Hat Enterprise Linux 5 is not affected by this flaw, as it shipped with an older version of Xen.
Mitigation
There is no known workaround for x86 32-bit Domain 0. The issue can be avoided by reducing the number of event channels available to the guest to no more than 1023. For example, setting `max_event_channels=1023` in the xl domain configuration, or deleting any existing setting (since 1023 is the default for xl/libxl).
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 | 5.5 | 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 | Unchanged | 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:L/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Other
Technical Impact: Quality Degradation; Varies by Context
Acknowledgements
Red Hat would like to thank the Xen project for reporting this issue.
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