CVE-2021-26933: Debian Linux

Medium severity, CVSS 5.5. EPSS: 0.3% chance of exploitation in the next 30 days.

An issue was discovered in Xen 4.9 through 4.14.x. On Arm, a guest is allowed to control whether memory accesses are bypassing the cache. This means that Xen needs to ensure that all writes (such as the ones during scrubbing) have reached the memory before handing over the page to a guest. Unfortunately, the operation to clean the cache is happening before checking if the page was scrubbed. Therefore there is no guarantee when all the writes will reach the memory.

Affected products

• Debian Debian Linux: version 10.0 only
• Fedoraproject Fedora: version 32 only; version 33 only
• Xen Xen: from 4.9.0, up to and including 4.14.1

Published 2021-02-17. Last modified 2026-06-17.