Anthropic's Claude Fable 5 Jailbreak Reveals Stack Exploits

!!️ Anthropic's Claude Fable 5 Jailbroken to Generate Stack Exploits | Source:

Anthropic launched Claude Fable 5 on June 9, 2026, as the first publicly available model in its new Mythos class, its most capable AI to date, excelling in software engineering, knowledge work, and vision benchmarks.

Researcher "Pliny the Liberator" defeats Claude Fable 5's safety classifiers using multi-agent decomposition, Unicode tricks, and narrative framing, leaking the model's 120,000-character system prompt along the way.

Screenshots shared by Pliny showed detailed outputs, including step-by-step stack buffer overflow exploitation guidance for x86 Linux systems, including disabling ASLR, writing vulnerable C server code with strcpy overflows, and compiling without protections — as well as the Birch reduction mechanism, a classic meth synthesis pathway.

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