In FFmpeg 4.0.1, due to a missing check for negative values of the mquant variable, the vc1_put_blocks_clamped function in libavcodec/vc1_block.c may trigger an out-of-array access while converting a crafted AVI file to MPEG4, leading to an information disclosure or a denial of service. https://nvd.nist.gov/vuln/detail/CVE-2018-13305
