An out-of-bounds write was addressed with improved input validation. This issue is fixed in iOS 14.2 and iPadOS 14.2, macOS Big Sur 11.0.1. Processing a maliciously crafted PDF may lead to arbitrary code execution.
CWE-787 - Out-of-Bounds Write
Out-of-bounds write vulnerability is a memory access bug that allows software to write data past the end or before the beginning of the intended buffer. This may result in the corruption of data, a crash, or arbitrary code execution.