Claude Users Report Visible Injection Prompts Appearing Unprompted Mid-Conversation

r/ClaudeAI·medium signal

A highly upvoted r/ClaudeAI thread (467 points) reports Claude inserting what appears to be an injection prompt at the end of its message during normal conversation, with Claude subsequently denying it ever produced the text. This is consistent with either a system prompt leaking into output, a cached context collision, or an MCP tool injecting content. For vibe coding users running multiple MCP servers, this is a practical security signal — inspect your tool chain if you see unexpected instructional text in Claude's responses.