#claude-haiku

October 16, 2026

HTTP response headers are an indirect-prompt-injection surface, but observed malicious attempts remain sparse. Researchers examined 217.1 million responses—10% of Common Crawl’s September 2026 crawl of 2.17 billion pages—and found 7,959 sites sending AI-directed headers. Of those, 7,271 pointed agents toward another resource such as llms.txt or an MCP server; only 30 sites contained injection attempts, most apparently pranks. Claude Opus, Claude Sonnet and Claude Haiku in Claude Code noticed test headers but did not act by default. They complied in 7 of 9 runs when the user prompt explicitly authorized following the site’s directions, showing why fetch tools should treat headers and their destinations as untrusted inputs. Signals Corps published the study. (discussion) · AI & Agent Security