The nsScannerString::AppendUnicodeTo function in Mozilla Firefox before 45.0 and Firefox ESR 38.x before 38.7 does not verify that memory allocation succeeds, which allows remote attackers to execute arbitrary code or cause a denial of service (out-of-bounds read) via crafted Unicode data in an HTML, XML, or SVG document.
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.