The 'fromIntegral' function in the 'base' package versions >=4.15.0.0 and <4.15.1.0 may produce conversion errors under optimization flags -O1 or -O2. These errors occur when converting negative Int values to Natural without throwing an underflow error, and when converting large Integer values greater than 2^64 to Natural, causing overflow. While primarily causing availability and data integrity issues, these errors can potentially lead to more severe security flaws such as buffer overflows in certain contexts. A fix is available in version 4.15.1.0.