• Calif researchers used Anthropic’s Mythos Preview to chain two bugs and techniques into a macOS kernel exploit on Apple M5
• The exploit bypassed Apple’s new Memory Integrity Enforcement, achieving root shell in five days despite years of Apple investment
• Attack highlights Mythos’ power in surfacing unknown flaws; Apple is reportedly working on a fix

Cybersecurity researchers Calif have explained how they used Anthropic’s (now) famed Mythos Preview AI tool to create a working macOS kernel memory corruption exploit on Apple’s newest M5 silicon, warning their work was a “glimpse of what’s coming” for hardware and software that was built “in a world before Mythos Preview.”

In September 2025, Apple introduced a new security feature designed to block hacking techniques that exploit software memory flaws.

Called Memory Integrity Enforcement (MIE), the feature uses hardware-level memory checks to stop malicious code from accessing data it shouldn’t. It was released alongside the iPhone 17 lineup and the new A19 chips.

Execution model persists

In April 2026, Anthropic allowed a handful of technology companies, including Calif, to access Mythos Preview, so they could get a head start on everyone else and secure their environments.

The company claimed Mythos was capable of surfacing unknown vulnerabilities and creating working exploits and as such was too dangerous to just be released to the general public.

Calif used Mythos to link “two bugs and a handful of techniques to corrupt the Mac’s memory and then gain access to parts of the device that should be inaccessible.” Commenting on their findings, the Calif team said Apple spent five years and “probably billions” of dollars to build MIE, while they managed to break it in five days.

“The exploit is a data-only kernel local privilege escalation chain targeting macOS 26.4.1 (25E253),” Calif said in a Substack post. “It starts from an unprivileged local user, uses only normal system calls, and ends with a root shell. The implementation path involves two vulnerabilities and several techniques, targeting bare-metal M5 hardware with kernel MIE enabled.”

Apparently, Apple is currently working on a fix. Probably using Mythos, too.

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Sead is a seasoned freelance journalist based in Sarajevo, Bosnia and Herzegovina. He writes about IT (cloud, IoT, 5G, VPN) and cybersecurity (ransomware, data breaches, laws and regulations). In his career, spanning more than a decade, he’s written for numerous media outlets, including Al Jazeera Balkans. He’s also held several modules on content writing for Represent Communications.