A NULL pointer dereference issue was found in the block mirror layer of QEMU in versions prior to 6.2.0. The 'self' pointer is dereferenced in mirror_wait_on_conflicts() without ensuring that it's not NULL. A malicious unprivileged user within the guest could use this flaw to crash the QEMU process on the host when writing data reaches the threshold of mirroring node. https://nvd.nist.gov/vuln/detail/CVE-2021-4145