CVE-2026-48710 — Starlette has missing Host header validation that poisons request.url.path, bypassing path-based security checks

Description (CNA)

Starlette is a lightweight ASGI framework/toolkit. Prior to version 1.0.1, the HTTP `Host` request header was not validated before being used to reconstruct `request.url`. Because the routing algorithm relies on the raw HTTP path while `request.url` is rebuilt from the `Host` header, a malformed header could make `request.url.path` differ from the path that was actually requested. Middleware and endpoints that apply security restrictions based on `request.url` (rather than the raw `scope` path) could therefore be bypassed. Users should upgrade to a version greater than or equal to version 1.0.1, which validates the `Host` header against the grammar of RFC 9112 §3.2 / RFC 3986 §3.2.2 when constructing `request.url` and falls back to `scope["server"]` for malformed values.

Affected (CNA)

Vendor / product	Versions
Kludex / starlette	affected < 1.0.1

CWE

CWE-444

References

ADP enrichment

CISA-ADP

No English description supplied.

redhat-SADP

A flaw was found in Starlette, a lightweight ASGI (Asynchronous Server Gateway Interface) framework. A remote attacker could exploit this vulnerability by sending a specially crafted HTTP `Host` request header. This malformed header could cause the `request.url` to be incorrectly reconstructed, leading to a discrepancy with the actual requested path. Consequently, security restrictions enforced by middleware and endpoints that rely on `request.url` for validation could be bypassed, potentially allowing unauthorized access or actions.