CVE-2020-25597
Description
A logic flaw was found in the handling of event channel operations in Xen. Operations such as resetting all event channels may involve decreasing one of the bounds checked when determining validity. 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
All Xen versions from 4.4 onwards are vulnerable. Red Hat Enterprise Linux 5 is not affected by this flaw, as it shipped an older version of Xen.
Mitigation
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).
For ARM systems, any limit no more than 4095 is safe. For 64-bit x86 PV guests, any limit no more than 4095 is likewise safe if the host configuration prevents the guest administrator from substituting and running a 32-bit kernel (and thereby putting the guest into 32-bit PV mode).
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 | 6.5 | 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 | 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:L/UI:N/S:C/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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