The html package (aka x/net/html) through 2018-09-25 in Go mishandles <math><template><mn><b></template>, leading to a "panic: runtime error" (index out of range) in (*insertionModeStack).pop in node.go, called from inHeadIM, during an html.Parse call.
The product uses untrusted input when calculating or using an array index, but the product does not validate or incorrectly validates the index to ensure the index references a valid position within the array.