A stack-based buffer overflow in the subtitle decoder in Libav 12.3 allows attackers to corrupt the stack via a crafted video file in Matroska format, because srt_to_ass in libavcodec/srtdec.c misuses snprintf.

References

• https://nvd.nist.gov/vuln/detail/CVE-2019-9720
• https://github.com/libav/libav/blob/df744e3cf66548c9167ea857104a29d2ea92819e/libavcodec/srtdec.c#L161
• https://lgtm.com/security/