LibreOffice Calc compiles cell formulas when opening a spreadsheet. A heap buffer overflow existed when compiling a very long formula made up of many opening tokens. The array that tracks nesting depth was allocated one element too small for that worst case, so such a formula wrote one element past its end. In fixed versions the array is sized to hold the largest possible nesting.
Weakness
A product calculates or uses an incorrect maximum or minimum value that is 1 more, or 1 less, than the correct value.