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CVE-2020-25597

Status Candidate

Overview

An issue was discovered in Xen through 4.14.x. There is mishandling of the constraint that once-valid event channels may not turn invalid. Logic in the handling of event channel operations in Xen assumes that an event channel, once valid, will not become invalid over the life time of a guest. However, operations like the resetting of all event channels may involve decreasing one of the bounds checked when determining validity. This may lead to bug checks triggering, crashing the host. An unprivileged guest may be able to crash Xen, leading to a Denial of Service (DoS) for the entire system. All Xen versions from 4.4 onwards are vulnerable. Xen versions 4.3 and earlier are not vulnerable. Only systems with untrusted guests permitted to create more than the default number of event channels are vulnerable. This number depends on the architecture and type of guest. For 32-bit x86 PV guests, this is 1023; for 64-bit x86 PV guests, and for all ARM guests, this number is 4095. Systems where untrusted guests are limited to fewer than this number are not vulnerable. Note that xl and libxl limit max_event_channels to 1023 by default, so systems using exclusively xl, libvirt+libxl, or their own toolstack based on libxl, and not explicitly setting max_event_channels, are not vulnerable.

Related Files

Ubuntu Security Notice USN-5617-1
Posted Sep 19, 2022
Authored by Ubuntu | Site security.ubuntu.com

Ubuntu Security Notice 5617-1 - It was discovered that memory contents previously stored in microarchitectural special registers after RDRAND, RDSEED, and SGX EGETKEY read operations on Intel client and Xeon E3 processors may be briefly exposed to processes on the same or different processor cores. A local attacker could use this to expose sensitive information. Julien Grall discovered that Xen incorrectly handled memory barriers on ARM-based systems. An attacker could possibly use this issue to cause a denial of service, obtain sensitive information or escalate privileges.

tags | advisory, denial of service, local
systems | linux, ubuntu
advisories | CVE-2020-0543, CVE-2020-11739, CVE-2020-11742, CVE-2020-15563, CVE-2020-15564, CVE-2020-15565, CVE-2020-15566, CVE-2020-15567, CVE-2020-25595, CVE-2020-25596, CVE-2020-25597, CVE-2020-25599, CVE-2020-25600, CVE-2020-25601
SHA-256 | 650005c21b26b7970b9035b36b8dca3aa7d9fbba307cbcf7d4eded34c754cfb8
Debian Security Advisory 4769-1
Posted Oct 28, 2020
Authored by Debian | Site debian.org

Debian Linux Security Advisory 4769-1 - Multiple vulnerabilities have been discovered in the Xen hypervisor, which could result in denial of service, guest-to-host privilege escalation or information leaks.

tags | advisory, denial of service, vulnerability
systems | linux, debian
advisories | CVE-2020-25595, CVE-2020-25596, CVE-2020-25597, CVE-2020-25599, CVE-2020-25600, CVE-2020-25601, CVE-2020-25602, CVE-2020-25603, CVE-2020-25604
SHA-256 | e6c5001c6e839fbf6f78b7b8d62d2d143bd2b61990509f9e7883301ff985de3e
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