Xpdf prior to version 4.04 contains an integer overflow in the JBIG2 decoder (JBIG2Stream::readTextRegionSeg() in JBIG2Stream.cc). Processing a specially crafted PDF file or JBIG2 image could lead to a crash or the execution of arbitrary code. This is similar to the vulnerability described by CVE-2021-30860 (Apple CoreGraphics).
An integer overflow was addressed with improved input validation. This issue is fixed in Security Update 2021-005 Catalina, iOS 14.8 and iPadOS 14.8, macOS Big Sur 11.6, watchOS 7.6.2. Processing a maliciously crafted PDF may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited.