CVE-2020-25600: An issue was discovered in Xen through 4.14.x. Out of bounds event channels are available to 32-bit x86 domains. The so called 2-level event channel m...

Description

An issue was discovered in Xen through 4.14.x. Out of bounds event channels are available to 32-bit x86 domains. The so called 2-level event channel model imposes different limits on the number of usable event channels for 32-bit x86 domains vs 64-bit or Arm (either bitness) ones. 32-bit x86 domains can use only 1023 channels, due to limited space in their shared (between guest and Xen) information structure, whereas all other domains can use up to 4095 in this model. The recording of the respective limit during domain initialization, however, has occurred at a time where domains are still deemed to be 64-bit ones, prior to actually honoring respective domain properties. At the point domains get recognized as 32-bit ones, the limit didn't get updated accordingly. Due to this misbehavior in Xen, 32-bit domains (including Domain 0) servicing other domains may observe event channel allocations to succeed when they should really fail. Subsequent use of such event channels would then possibly lead to corruption of other parts of the shared info structure. An unprivileged guest may cause another domain, in particular Domain 0, to misbehave. This may lead 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 x86 32-bit domains servicing other domains are vulnerable. Arm systems, as well as x86 64-bit domains, are not vulnerable.

Metrics

CVSS 3.1

5.5/10

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

0.43%

34.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-787

Affected Software

Vendor	Product	Versions
Xen	Xen	>= 4.4.0, <= 4.14.0
Fedoraproject	Fedora	31
Fedoraproject	Fedora	32
Fedoraproject	Fedora	33
Opensuse	Leap	15.2
Debian	Debian Linux	10.0

References

Timeline

Published: Sep 23, 2020
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2020-25600?

An issue was discovered in Xen through 4.14.x. Out of bounds event channels are available to 32-bit x86 domains. The so called 2-level event channel model imposes different limits on the number of usable event channels for 32-bit x86 domains vs 64-bit or Arm (either bitness) ones. 32-bit x86 domains can use only 1023 channels, due to limited space in their shared (between guest and Xen) information structure, whereas all other domains can use up to 4095 in this model. The recording of the respective limit during domain initialization, however, has occurred at a time where domains are still deemed to be 64-bit ones, prior to actually honoring respective domain properties. At the point domains get recognized as 32-bit ones, the limit didn't get updated accordingly. Due to this misbehavior in Xen, 32-bit domains (including Domain 0) servicing other domains may observe event channel allocations to succeed when they should really fail. Subsequent use of such event channels would then possibly lead to corruption of other parts of the shared info structure. An unprivileged guest may cause another domain, in particular Domain 0, to misbehave. This may lead 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 x86 32-bit domains servicing other domains are vulnerable. Arm systems, as well as x86 64-bit domains, are not vulnerable.

How severe is CVE-2020-25600?

CVE-2020-25600 has a CVSS score of 5.5/10 (MEDIUM severity). The EPSS model estimates a 0.43% probability of exploitation in the next 30 days.

How do I fix CVE-2020-25600?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.