Is CVE-2026-42271 in the CISA Known Exploited Vulnerabilities catalog?

CVE-2026-42271 is not currently listed in the CISA KEV catalog.

Which frameworks does CVE-2026-42271 affect?

CVE-2026-42271 affects FastAPI.

Vulnerability intelligence

CVE-2026-42271 — FastAPI Vulnerability

A malformed Host header bypasses authentication in Starlette — the ASGI framework underneath FastAPI and most of Python's AI agent infrastructure. Modern frameworks are not immune. The difference is how fast they patch.

CVSS 8.7 FastAPI 2026

What WebPulse reported · 1 analysis

CVE-2026-48710 'BadHost': The Vulnerability That Hit FastAPI, vLLM, LiteLLM, and 325 Million Weekly Downloads.

A malformed Host header bypasses authentication in Starlette — the ASGI framework underneath FastAPI and most of Python's AI agent infrastructure. Modern framew

June 14, 2026

View CVE-2026-42271 on the NIST National Vulnerability Database →

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