Anthropic

Claude Fable 5 Jailbreak Attacks Bypass Fallback Defense

ATLAS OWASP MEDIUM ▲ 7.2 SecurityWeek Jun 10, 2026

Anthropic has released Claude Fable 5, a high-capability 'Mythos-class' model that automatically falls back to a less capable model (Claude Opus 4.8) when queries touch sensitive domains like cybersecurity and biology. The company conducted over 1,000 hours of external red-teaming with no universal jailbreaks discovered, though it openly acknowledges financially motivated adversaries will attempt to circumvent these controls. Trusted cybersecurity partners under Project Glasswing receive elevated access to the full Mythos 5 capabilities, raising questions about insider risk and tiered trust model security.

Claude Mythos Generates Working Exploits for Firefox, Windows

ATLAS OWASP CRITICAL ▲ 9.2 SecurityWeek Jun 10, 2026

Anthropic's Claude Mythos Preview model demonstrated the ability to generate functional proof-of-concept exploits targeting known Firefox and Windows vulnerabilities within minutes to hours, compressing the traditional patch gap window dramatically. Testing also revealed that public Anthropic models with safety guardrails disabled could produce working exploits, though at a lower success rate than Mythos. The findings underscore how frontier LLMs are shifting the threat landscape for unpatched N-day vulnerabilities by automating and accelerating exploit development previously bottlenecked by scarce reverse engineering expertise.

Anthropic Claude Code Prompt Injection Leaks Secrets

ATLAS OWASP HIGH ▲ 9.1 Microsoft Security Blog Jun 08, 2026

Microsoft Threat Intelligence disclosed a vulnerability in Anthropic's Claude Code GitHub Action whereby prompt injection via untrusted GitHub content — issue bodies, PR descriptions, and comments — could cause the AI agent to read sensitive environment variables, including the ANTHROPIC_API_KEY, from /proc/self/environ. The flaw stemmed from inconsistent sandboxing: while subprocess execution paths like Bash were scrubbed of environment variables, the Read tool had no equivalent restriction. Anthropic patched the issue in Claude Code version 2.1.128 by blocking access to sensitive /proc filesystem paths.

Claude Mythos Unauthorized Access Exposes AI Security

ATLAS OWASP HIGH ▲ 7.2 The Hacker News Jun 08, 2026

A reported unauthorized access to Anthropic's Claude Mythos model within hours of its limited technical preview highlights acute security risks as agentic AI is deployed across classified defense and intelligence networks. The incident underscores vulnerabilities specific to AI infrastructure in high-security environments, including training data poisoning, access control failures, and cross-domain classification boundary erosion. Secure IT infrastructure, governed access, and cross-domain data controls are identified as prerequisites for safe AI deployment at mission scale.

Claude Sandbox Escape Enables Credential Exfiltration

ATLAS OWASP MEDIUM ▲ 7.2 Simon Willison May 31, 2026

Anthropic has published detailed documentation of its sandboxing architecture across Claude.ai, Claude Code, and Claude Cowork, including disclosure of a previously identified credential exfiltration vector via the api.anthropic.com/v1/files endpoint. The writeup covers process-level isolation technologies including gVisor, Seatbelt, Bubblewrap, and full VM approaches, and candidly acknowledges security gaps that were missed. This transparency is notable for the agentic AI space, where sandbox documentation is typically sparse and trust is difficult to calibrate.

mouse5212-super-formatter npm Malware Steals Claude Files

ATLAS OWASP HIGH ▲ 8.2 The Hacker News May 29, 2026

A malicious npm package named 'mouse5212-super-formatter' was discovered exfiltrating files from Anthropic's Claude AI user directory by authenticating to a threat actor-controlled GitHub repository. The package disguised itself as a legitimate archive utility while silently uploading all local workspace files during the postinstall phase. Notably, the attacker's poor operational security — including a leaked GitHub token — suggests AI-generated malware with minimal human oversight, pointing to a growing trend of low-skill threat actors leveraging AI to produce supply chain malware.

CVE-2026-5194: Anthropic Claude Discovers 10,000+ Flaws

ATLAS OWASP HIGH ▲ 8.5 The Hacker News May 25, 2026

Anthropic's Project Glasswing has deployed Claude Mythos Preview — a frontier AI model — to autonomously discover over 10,000 high- and critical-severity vulnerabilities across widely used open-source software, with 1,094 confirmed as valid high/critical flaws. The initiative highlights a growing asymmetry: AI is accelerating vulnerability discovery far faster than the security community can remediate, compressing patch windows and raising the stakes for defenders. Anthropic is now urging shorter patch cycles and hardened defaults, warning that comparable offensive capabilities could soon be broadly accessible to threat actors.

Mythos AI Exploits macOS Kernel Memory Corruption

ATLAS OWASP HIGH ▲ 7.5 Schneier on Security May 22, 2026

A threat group leveraged Anthropic's Mythos AI model to identify and exploit a kernel memory corruption vulnerability in Apple's M5 chip running macOS. This represents a concrete, reported instance of AI-assisted vulnerability research being used offensively to discover low-level hardware-adjacent exploits. The incident underscores the dual-use danger of increasingly capable AI coding and reasoning models in the hands of adversarial actors.

Claude Chrome Extension Prompt Injection Enables Agent Takeover

ATLAS OWASP HIGH ▲ 9.1 SecurityWeek May 09, 2026

A vulnerability dubbed ClaudeBleed in Anthropic's Claude Chrome extension allows any browser extension to inject arbitrary prompts into the Claude AI agent by exploiting lax permission checks and improper trust validation. Attackers can bypass user confirmation protections via DOM manipulation and repeated message forging, enabling full agent takeover for information theft or unauthorized actions. The flaw effectively breaks Chrome's extension security model and exposes users running Claude's agentic capabilities to third-party extension compromise.

Firefox Vulnerabilities Discovered via AI-Assisted Fuzzing

ATLAS OWASP HIGH ▲ 7.2 Simon Willison May 08, 2026

Mozilla used early access to Anthropic's Claude Mythos model to systematically discover and patch hundreds of previously unknown vulnerabilities in Firefox, including bugs over 15–20 years old. The effort demonstrates a step-change in AI-assisted vulnerability research, with April 2026 seeing 423 security fixes compared to a monthly baseline of 20–30. The same capability that empowered Mozilla's defenders also signals that adversaries with similar model access could industrialise exploit discovery against open-source software at scale.

Claude Code OAuth Token Theft via npm Supply Chain

ATLAS OWASP HIGH ▲ 9.1 SecurityWeek May 08, 2026

Mitiga Labs has disclosed a stealthy attack chain targeting Claude Code's MCP infrastructure, allowing adversaries to silently intercept OAuth tokens by redirecting MCP traffic through attacker-controlled infrastructure. The attack requires only the ability to install a malicious npm package, which modifies ~/.claude.json to insert a proxy and pre-sets trust flags to suppress security prompts. Because the OAuth token grants broad access to all connected SaaS tools, successful exploitation effectively hands attackers a persistent master key to the victim's integrated development environment.

Anthropic Releases Claude Security Vulnerability Scanner

ATLAS OWASP HIGH ▲ 7.2 SecurityWeek May 01, 2026

Anthropic has released Claude Security in public beta, a dedicated vulnerability scanning product aimed at countering the accelerating threat of AI-powered exploitation exemplified by its own Mythos model. The tool integrates directly into Claude Enterprise, scanning repositories for vulnerabilities, providing confidence-rated findings, and generating targeted patches — compressing the security team-to-engineer remediation cycle from days to a single session. The launch reflects a broader industry acknowledgment that frontier AI models in adversarial hands are fundamentally shortening time-to-exploit, forcing defenders to adopt equivalent AI-native tooling.

GPT-5.5 Matches Claude Mythos in Vulnerability Discovery

ATLAS OWASP HIGH ▲ 7.2 Simon Willison May 01, 2026

The UK's AI Security Institute has evaluated OpenAI's GPT-5.5 for offensive cybersecurity capabilities, finding it comparable to Anthropic's Claude Mythos model in identifying security vulnerabilities. Unlike Mythos, GPT-5.5 is generally available, meaning its vulnerability-discovery capabilities are accessible to a broad population including malicious actors. This raises significant concerns about the proliferation of AI-assisted exploitation tools at scale.

CVE-2026-42208: LiteLLM SQL Injection Exposes API Keys

ATLAS OWASP CRITICAL ▲ 9.2 The Hacker News Apr 30, 2026

A critical SQL injection vulnerability (CVE-2026-42208, CVSS 9.3) in BerriAI's LiteLLM AI gateway was actively exploited within 36 hours of public disclosure, targeting database tables storing upstream LLM provider API keys including OpenAI, Anthropic, and AWS Bedrock credentials. Attackers demonstrated prior knowledge of LiteLLM's internal schema, selectively probing credential and configuration tables while ignoring user and team tables. The blast radius extends far beyond a typical web-app SQL injection, as successful extraction equates to cloud-account-level compromise across multiple AI provider accounts.

CVE-2026-42208: LiteLLM SQL Injection Stealing AI Credentials

ATLAS OWASP CRITICAL ▲ 9.2 BleepingComputer Apr 29, 2026

A critical unauthenticated SQL injection vulnerability (CVE-2026-42208) in LiteLLM, a widely-used LLM proxy and SDK middleware, is being actively exploited to extract API keys, provider credentials, and configuration secrets from the proxy database. Exploitation began within 36 hours of public disclosure, with attackers demonstrating precise targeting of sensitive tables containing OpenAI, Anthropic, and Bedrock credentials. The stolen credentials could enable downstream attacks against AI infrastructure at scale, given LiteLLM's broad adoption across LLM application ecosystems.

Anthropic

Stay ahead of the threat.