CVE-2026-80921

A flaw was found in the Linux kernel's KVM s390 Virtual Shared Inter-Partition Emulation (VSIE) component. When shadowing crypto access bits from a format0 apcb, stale crypto bits were not properly cleared. This oversight could allow a nested guest to potentially access a device that should no longer be available, leading to unauthorized information disclosure or access to resources.

This vulnerability is rated as Important because an unprivileged nested guest could retain unauthorized access to cryptographic coprocessor resources, potentially compromising sensitive cryptographic data and device isolation. The issue exclusively impacts IBM Z (s390x) systems deploying KVM nested virtualization with cryptographic adapter sharing enabled. Deployments on non-s390x hardware architectures and systems that do not execute nested KVM guests on s390x are not affected.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.