Qemu-kvm: uefi-vars: information disclosure vulnerability in uefi_vars_write callback

Vulnerability Description

A flaw was found in QEMU in the uefi-vars virtual device. When the guest writes to register UEFI_VARS_REG_BUFFER_SIZE, the .write callback `uefi_vars_write` is invoked. The function allocates a heap buffer without zeroing the memory, leaving the buffer filled with residual data from prior allocations. When the guest later reads from register UEFI_VARS_REG_PIO_BUFFER_TRANSFER, the .read callback `uefi_vars_read` returns leftover metadata or other sensitive process memory from the previously allocated buffer, leading to an information disclosure vulnerability.

References

• https://access.redhat.com/security/cve/CVE-2025-8860
• https://bugzilla.redhat.com/show_bug.cgi?id=2387588