An exploitable memory corruption vulnerability exists in the JBIG2 parser of Artifex MuPDF 1.9. A specially crafted PDF can cause a negative number to be passed to a memset resulting in memory corruption and potential code execution. An attacker can specially craft a PDF and send to the victim to trigger this vulnerability.
https://www.talosintelligence.com/vulnerability_reports/TALOS-2016-0243