An out-of-bounds read was addressed with improved input validation. This issue is fixed in iOS 12.4, macOS Mojave 10.14.6, tvOS 12.4, watchOS 5.3. Parsing a maliciously crafted office document may lead to an unexpected application termination or arbitrary code execution.
https://support.apple.com/HT210353
https://support.apple.com/HT210351