A flaw was found in the am53c974 SCSI controller emulation of QEMU. When an SCSI layer transfer is incorrectly terminated, it is possible for a TI command to cause an SCSI buffer overflow due to the expected transfer data length being less than the available data in the FIFO. When this occurs, the unsigned async_len variable underflows and becomes a large offset, which writes past the end of the allocated SCSI buffer. This flaw could allow a malicious guest to crash QEMU and cause a denial of service condition.