CVE-2026-48710: starlette: Starlette: Security restriction bypass via malformed HTTP Host header
Component: starlette
Severity: Critical
CWE: CWE-1289 (Improper Validation of Unsafe Equivalence in Input)
CVSS v3: 6.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N)
Public date: 2026-05-26T21:54:54.393000+00:00

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.

Statement: The impact is rated as Critical because path-based authentication and access control middleware can be completely bypassed by an unauthenticated remote attacker using a crafted HTTP Host header.

Starlette reconstructs `request.url` by combining the HTTP Host header value with the request path, but performs no validation on the Host header. An attacker can inject path separators or query characters into the Host header (e.g., `Host: example.com/health?x=`), causing `request.url.path` to return a value that differs from the actual HTTP `request path` used for routing. Middleware that enforces authentication or authorization decisions based on `request.url.path` will evaluate the injected path rather than the real one, allowing the attacker to reach protected endpoints.

With regard to CVSS metrics, the Attack Vector (AV) is Network and Privileges Required (PR) is None, because the attack requires only the ability to send HTTP requests with a crafted Host header. User interaction is not required.

Red Hat Satellite / Insights (IoP): The starlette package is included as a dependency of Connexion, but this flaw is rated Low impact because these services do not use path-based authentication middleware and all services are deployed behind reverse proxies. 

OpenShift Lightspeed (OLS): The starlette package is included as a dependency, but this flaw is rated Low impact because authentication is enforced via Kubernetes TokenReview/SubjectAccessReview through FastAPI dependency injection, not path-based middleware; request.url.path is only used for metrics and response header application.

RHOAI Kubeflow Training images: starlette is being used as indirect dependency of mlflow, but this flaw is rated as Low impact because mlflow is used as client library only to store training metrics on remote server, it doesn't expose any endpoint.

RHOAI odh-automl: The impact is reduced to Low since starlette is only used in the backend and it's transient dependency and starlette is not used at all to serve any endpoints.

RHOAI odh-kserve-autogluon-server-rhel9: While the Starlette dependency is present in the build, the vulnerable code in starlette is not reachable. This reduces the impact to low.

Affected upstream versions: < 1.0.1
Fixed upstream versions: 1.0.1
Upstream repository: https://github.com/Kludex/starlette
Upstream fix commit: 764dab0dcfb9033d75442d7a359645c9f94648c6