CVE-2026-48710

Kludex Starlette prior to version 1.0.1 did not validate the HTTP Host request header before using it to reconstruct request.url, an inconsistency classified as HTTP request/response smuggling (CWE-444). Because routing operates on the raw ASGI scope path while request.url is rebuilt from the unvalidated Host header, an attacker can send a malformed Host header so that request.url.path differs from the path the router actually processed. Any middleware or endpoint that enforces security restrictions based on request.url rather than the raw scope path can then be tricked into approving requests that should have been blocked, bypassing those controls. All Starlette deployments below 1.0.1 are affected, both direct users and downstream products that bundle the library, including Red Hat offerings such as Ansible Automation Platform, OpenShift AI, OpenShift Lightspeed, Satellite, AI Inference Server, Migration Toolkit for Applications, and Enterprise Linux AI. CISA added the flaw to the Known Exploited Vulnerabilities catalog on 2026-09-02, confirming active exploitation; related reporting describes attackers deploying reverse shells and crypto miners, and EPSS ranks it in the 98th percentile with a 36.3% probability of exploitation within 30 days.

What to do: Upgrade Starlette to 1.0.1 or later, which validates the Host header against RFC 9112/RFC 3986 grammar and falls back to scope['server'] for malformed values, and apply the corresponding Red Hat updates for each bundled product listed above. Until patched, review middleware and endpoints that enforce security decisions from request.url and validate or pin the Host header at your reverse proxy or load balancer. As a KEV entry, federal agencies must patch per BOD 26-04 timelines based on each asset's internet exposure, and operators of internet-facing AI infrastructure should verify their Starlette/FastAPI dependency versions.