VLC media player 3.0.20 and earlier is vulnerable to denial of service through an integer overflow which could be triggered with a maliciously crafted mms stream (heap based overflow). If successful, a malicious third party could trigger either a crash of VLC or an arbitrary code execution with the target user's privileges.
A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().