Anthropic

Anthropic Mythos Preview Breached via Contractor Credentials

ATLAS OWASP HIGH ▲ 8.2 Wired Security Apr 26, 2026

A group of Discord users gained unauthorized access to Anthropic's restricted Mythos Preview AI model by combining data from a third-party breach, educated guessing about model endpoint URLs, and leveraging existing contractor permissions. The incident exposes systemic weaknesses in how access controls for powerful, restricted AI models are enforced across contractor and supply chain boundaries. This is particularly significant given Mythos's described capability as an advanced vulnerability-discovery tool, raising the stakes if malicious actors replicate the access method.

Anthropic Claude Memory Poisoning Enables Prompt Injection

ATLAS OWASP HIGH ▲ 8.2 Dark Reading Apr 24, 2026

Cisco researchers discovered and reported a significant vulnerability in how Anthropic's AI systems handle memory files, which has since been patched. The flaw highlights a broader, systemic risk in agentic AI architectures where persistent memory mechanisms can be exploited to inject malicious instructions or exfiltrate sensitive data across sessions. Security experts caution that memory mismanagement in AI agents represents an enduring attack surface that extends well beyond any single vendor fix.

Anthropic Mythos AI Achieves 72% Autonomous Exploit Success

ATLAS OWASP CRITICAL ▲ 9.2 The Hacker News Apr 24, 2026

Anthropic's Project Glasswing, powered by the Mythos Preview model, demonstrated unprecedented AI-driven vulnerability discovery — including a 72.4% autonomous exploit success rate against Firefox's JS shell and chained multi-bug exploits bypassing OS sandboxing — but fewer than 1% of discovered vulnerabilities were patched before potential adversarial access. The disclosure reveals a catastrophic asymmetry: AI has industrialised vulnerability discovery at machine speed while remediation capacity remains locked to human calendar pace. Real-world threat actors are already deploying LLM-integrated attack chains autonomously, as evidenced by an MCP-hosted LLM used against FortiGate appliances.

Claude Supply Chain Attack: SentinelOne EDR Blocks LLM

ATLAS OWASP HIGH ▲ 7.5 SentinelOne Blog Apr 23, 2026

SentinelOne claims its AI-powered EDR autonomously detected and blocked Anthropic's Claude LLM from executing a zero-day supply chain attack, representing a significant case study in agentic AI systems operating as attack vectors. The incident highlights the emerging threat surface created when LLMs are granted autonomous execution capabilities within enterprise environments. This appears to be a vendor marketing piece, and the claims warrant independent verification, but the scenario it describes — an AI agent compromising supply chain integrity — is technically credible and aligns with known agentic AI risk models.

Firefox: 271 Vulnerabilities Found via AI-Assisted Discovery

ATLAS OWASP MEDIUM ▲ 7.2 Simon Willison Apr 22, 2026

Firefox CTO Bobby Holley reports that a collaboration with Anthropic using an early version of Claude Mythos Preview identified 271 vulnerabilities in Firefox, resulting in fixes shipped in Firefox 150. This represents a significant real-world demonstration of AI-assisted vulnerability discovery at scale, signalling a shift in the defender-attacker dynamic. The findings suggest LLMs are becoming operationally viable tools for large-scale code security auditing.

Claude System Prompts Exposed via Git-Based Extraction

ATLAS OWASP MEDIUM ▲ 6.2 Simon Willison Apr 22, 2026

Simon Willison has created a git-based tool to track the evolution of Anthropic's publicly published Claude system prompts across model versions, enabling structured diff analysis of prompt changes over time. While the underlying prompts are intentionally public, the tooling lowers the barrier for adversarial reconnaissance — making it easier for threat actors to identify shifts in safety constraints, refusal heuristics, or behavioral guardrails between model releases. This kind of systematic prompt archaeology directly supports meta-prompt extraction and jailbreak development workflows.

CVE-2026: Anthropic MCP SDK Remote Code Execution

ATLAS OWASP CRITICAL ▲ 9.4 The Hacker News Apr 20, 2026

A systemic 'by design' vulnerability in Anthropic's Model Context Protocol (MCP) SDK enables arbitrary remote code execution across all supported language implementations via unsafe STDIO transport defaults, affecting over 7,000 publicly accessible servers and 150 million downloads. The flaw has been independently confirmed across 10+ popular AI frameworks including LiteLLM, LangChain, and Flowise, with Anthropic declining to modify the protocol's architecture. This represents a significant AI supply chain risk with cascading exposure to sensitive data, API keys, and internal systems.

Prompt Injection Risk: Claude 4.7 Agentic Tool Expansion

ATLAS OWASP MEDIUM ▲ 6.2 HN AI Security Apr 20, 2026

Anthropic's published system prompt diff between Claude Opus 4.6 and 4.7 reveals significant expansions in agentic tool access, autonomous browsing capabilities, and child safety guardrails — changes with direct security implications for prompt injection and excessive agency risks. The new `tool_search` mechanism and acting-before-asking posture increase the attack surface for adversarial inputs targeting agentic Claude deployments. Transparency in publishing these changes is notable, but the expanded autonomous capabilities warrant scrutiny from defenders.

Autonomous Exploit Generation: Claude Mythos Risk

ATLAS OWASP HIGH ▲ 8.5 Schneier on Security Apr 20, 2026

Bruce Schneier analyses Anthropic's Claude Mythos Preview and Project Glasswing, a controlled deployment programme aimed at finding and patching software vulnerabilities before the model is publicly released due to its advanced cyberattack capabilities. The piece highlights a growing offensive AI capability gap, noting that newer LLMs can autonomously chain memory corruption bugs and operationalise exploits without human orchestration, while observing that defenders currently retain a marginal advantage because vulnerability discovery is easier than exploitation. Schneier warns that this advantage is narrowing rapidly and that the industry must prepare for a world of commoditised zero-day exploits.

GPT-5.4-Cyber Expansion Raises LLM Jailbreak Dual-Use Risks

ATLAS OWASP MEDIUM ▲ 6.5 SecurityWeek Apr 17, 2026

OpenAI has expanded access to GPT-5.4-Cyber, a fine-tuned model designed for defensive cybersecurity applications, following Anthropic's reveal of its Mythos cybersecurity model. While framed as a defensive tool for legitimate security practitioners, the widened access to a capability-enhanced cybersecurity LLM raises dual-use concerns around potential misuse for offensive operations. The competitive dynamic between major AI labs in the security-focused model space signals a broader industry trend that warrants careful access control and policy scrutiny.

Anthropic MCP Supply Chain Flaw Enables Command Injection

ATLAS OWASP CRITICAL ▲ 9.1 SecurityWeek Apr 16, 2026

A structural vulnerability in Anthropic's Model Context Protocol (MCP) allows unsanitized commands to be executed silently within AI environments, potentially enabling full system compromise. Researchers classify the flaw as 'by design,' meaning it stems from architectural decisions rather than implementation bugs, making it particularly difficult to patch without protocol-level changes. The breadth of MCP adoption across agentic AI toolchains significantly amplifies the supply chain risk.

Claude Code Source Leak Exposes 512K Lines of Code

ATLAS OWASP MEDIUM ▲ 6.2 HN AI Security Apr 16, 2026

A packaging error exposed 512,000 lines of Claude Code's source, revealing severe code quality issues including a 3,167-line monolithic function, undocumented API waste, and regex-based sentiment analysis in an LLM product — raising questions about the security posture of AI-generated codebases. The disclosure highlights systemic risks when AI systems are used to self-develop production tooling without adequate human review or architectural oversight. These patterns represent meaningful supply chain and excessive agency concerns for enterprise users of Claude Code.

Anthropic Claude Mythos Sparks AI Vulnerability Storm Warning

ATLAS OWASP HIGH ▲ 7.2 Dark Reading Apr 14, 2026

The Cloud Security Alliance has issued a warning about an anticipated 'AI vulnerability storm' following the release of Anthropic's Claude Mythos model, urging CISOs to prepare defensive postures in advance of expected exploit activity. The advisory signals growing institutional concern that major LLM releases create systemic risk windows as adversaries probe new model capabilities and attack surfaces. Security leaders are being advised to treat post-release periods of frontier AI models as high-alert intervals requiring elevated monitoring and response readiness.

Anthropic Claude Prompt Injection Enables Excessive Agency

ATLAS OWASP LOW ▲ 6.2 CrowdStrike Blog Apr 11, 2026

CrowdStrike, as a founding member of Anthropic's Mythos program, is highlighting the security challenges posed by increasingly capable frontier AI models, signaling a growing industry focus on securing agentic and large-scale AI systems. The article underscores the philosophical and practical position that AI capability gains must be matched by proportional security investment. While the piece is primarily a vendor partnership announcement and executive viewpoint, it reflects an important industry trend toward formalising AI-specific security frameworks and tooling.

US summons bank bosses over cyber risks from Anthropic's latest AI model

ATLAS OWASP CRITICAL ▲ 8.5 HN AI Security Apr 10, 2026

The US Treasury convened major bank executives to discuss cybersecurity risks posed by Anthropic's unreleased Claude Mythos model, which the company claims has surpassed nearly all human experts at finding and exploiting software vulnerabilities. A code leak prompted Anthropic to publicly acknowledge the model's unprecedented offensive cyber capability, raising systemic financial sector risk concerns. The meeting signals growing regulatory awareness of AI-enabled cyber threats to critical financial infrastructure.

Anthropic

Stay ahead of the threat.