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wiredmikey shares a report from SecurityWeek: Security researchers at Google's Project Zero have picked apart one of the most notorious in-the-wild iPhone exploits and found a never-before-seen hacking roadmap that included a PDF file pretending to be a GIF image with a custom-coded virtual CPU built out of boolean pixel operations. If that makes you scratch your head, that was exactly the reaction from Google's premier security research team after disassembling the so-called FORCEDENTRY iMessage zero-click exploit used to plant NSO Group's Pegasus surveillance tool on iPhones. "We assess this to be one of the most technically sophisticated exploits we've ever seen," Google's Ian Beer and Samuel Grob wrote in a technical deep-dive into the remote code execution exploit that was captured during an in-the-wild attack on an activist in Saudi Arabia. In its breakdown, Project Zero said the exploit effectively created "a weapon against which there is no defense," noting that zero-click exploits work silently in the background and does not even require the target to click on a link or surf to a malicious website. "Short of not using a device, there is no way to prevent exploitation by a zero-click exploit," the research team said. The researchers confirmed the initial entry point for Pegasus was Apple's proprietary iMessage that ships by default on iPhones, iPads and macOS devices. By targeting iMessage, the NSO Group hackers needed only a phone number of an AppleID username to take aim and fire eavesdropping implants. Because iMessage has native support for GIF images (especially those that loop endlessly), Project Zero's researchers found that this expanded the attack surface and ended up being abused in an exploit cocktail that targeted a security defect in Apple's CoreGraphics PDF parser. Within Apple's CoreGraphics PDF parser, the NSO exploit writers abused Apple's implementation of the open-source JBIG2, a domain specific image codec designed to compress images where pixels can only be black or white. Describing the exploit as "pretty terrifying," Google said the NSO Group hackers effectively booby-trapped a PDF file, masquerading as a GIF image, with an encoded virtual CPU to start and run the exploit. Apple patched the exploit in September and filed a lawsuit seeking to hold NSO Group accountable.