Memory corruption during text run construction (Windows) — Mozilla

Alex Miller reported that when very long strings were constructed and inserted into an HTML document, the browser would incorrectly construct the layout objects used to display the text. Under such conditions an incorrect length would be calculated for a text run resulting in too small of a memory buffer being allocated to store the text. This issue could be used by an attacker to write data past the end of the buffer and execute malicious code on a victim’s computer.