Critical

Anthropic’s Fable 5 Model Jailbroken Within Days

Schneier on Security

June 23, 2026 at 11:03 AM

Actively Exploited

Overview

Anthropic's Fable 5 model, designed to be a safer version of its Mythos Preview, has been compromised shortly after its release. The model was built with guardrails to prevent its misuse in creating cyberattacks. However, researchers discovered that these protections could be bypassed within days of the model becoming available. This incident raises concerns about the security of AI models and the potential for misuse, particularly as they become more integrated into various applications. The ability to circumvent these safety measures could lead to harmful applications, emphasizing the need for stronger safeguards in AI technologies.

Key Takeaways

Active Exploitation: This vulnerability is being actively exploited by attackers. Immediate action is recommended.
Affected Systems: Anthropic Fable 5, Mythos Preview
Timeline: Newly disclosed

Original Article Summary

Fable 5 is the supposed safe version of Anthropic’s Mythos Preview, with guardrails to ensure that it can’t be used to create cyberattacks. Well, that restriction was bypassed within days.

Impact

Anthropic Fable 5, Mythos Preview

Exploitation Status

This vulnerability is confirmed to be actively exploited by attackers in real-world attacks. Organizations should prioritize patching or implementing workarounds immediately.

Timeline

Newly disclosed

Remediation

Not specified

Additional Information

This threat intelligence is aggregated from trusted cybersecurity sources. For the most up-to-date information, technical details, and official vendor guidance, please refer to the original article linked below.

Related Topics: This incident relates to Vulnerability.

Read Original Article

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