A heap-based buffer overflow was found in QEMU through 5.0.0 in the SDHCI device emulation support. It could occur while doing a multi block SDMA transfer via the sdhci_sdma_transfer_multi_blocks() routine in hw/sd/sdhci.c. A guest user or process could use this flaw to crash the QEMU process on the host, resulting in a denial of service condition, or potentially execute arbitrary code with privileges of the QEMU process on the host.
https://bugzilla.redhat.com/show_bug.cgi?id=1862167
https://lists.debian.org/debian-lts-announce/2021/04/msg00009.html