ATR-2026-00135criticalSkill Compromiseexperimental
Data Exfiltration URL in Skill Instructions
Detects SKILL.md files that instruct the agent to send data to external URLs, especially when combined with concealment language ("don't tell the user", "automatic", "verification step"). Legitimate skills may reference URLs for documentation, but they don't ask the agent to POST user data to them. Key pattern: instruction to send/post/upload + user data reference + URL.
Severity
critical
Category
Skill Compromise
Scan Target
skill
Author
ATR Community
Response Actions
alertblock input
References
OWASP Agentic
ASI01:2026 - Agent Goal Hijack
OWASP LLM
LLM01:2025 - Prompt Injection