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CVE-2026-48710 is a security vulnerability discovered in Starlette, a lightweight ASGI framework and toolkit commonly used in asynchronous Python applications.
Prior to version 1.0.1, the framework failed to properly validate the HTTP Host request header before using it to reconstruct the `request.url` attribute.
When a client sends an HTTP request, the routing mechanism relies correctly on the raw ASGI scope path, dispatching the request to the intended endpoint.
However, components, middleware, or authorization checks that evaluate `request.url.path` instead of the raw path are vulnerable to manipulation.
An attacker can inject a malformed or specially crafted Host header containing characters outside the standard URI grammar, such as forward slashes, question marks, or hash symbols.
During URL reconstruction, Starlette concatenates the host and path components and re-parses the resulting string.
The injected characters alter the parsing boundaries, causing `request.url.path` to diverge from the actual path received by the server.
For example, a request sent to `/foo` with a modified Host header containing `/abc` will cause the router to successfully execute the `/foo` endpoint.
Simultaneously, middleware inspecting `request.url.path` will perceive the path as `/abc` instead of /foo.
If path-based security controls or access restrictions rely on request.url.path, this discrepancy allows unauthorized users to bypass middleware checks.
The vulnerability does not inherently modify routing behavior or grant direct access without application-level flaws.
Instead, it exposes an inconsistency between canonical ASGI request paths and reconstructed URLs utilized by custom middleware.
Deployments utilizing strict reverse proxies that reject malformed headers are inherently shielded from this vector.
Remediation requires updating Starlette and ensuring security logic adheres to canonical scopes.
DailyCVE Form:
Platform: Starlette
Version: Below version 1.0.1
Vulnerability: HTTP Request Smuggling
Severity: Medium severity level
date: May 26 2026
Prediction: Patched in June
What Undercode Say:
Bash commands and code snippets for verification and analysis:
Check installed Starlette version pip show starlette Upgrade Starlette to a secure release version pip install --upgrade "starlette>=1.0.1"
Example demonstrating safe scope path usage vs reconstructed url path
async def secure_middleware(scope, receive, send):
Always use the canonical scope path for security validation
path = scope["path"]
if not path.startswith("/api/public"):
Deny unauthorized access
pass
Exploit: (Educational Purposes!)
GET /secure-admin-panel HTTP/1.1 Host: vulnerable-server.local/public-endpoint?bypass=true User-Agent: Security-Researcher
Protection: from this CVE
Upgrade the Starlette package to version 1.0.1 or later where Host header validation is strictly enforced.
Ensure all application middleware and custom authorization checks utilize `scope[“path”]` instead of request.url.path.
Deploy an RFC-compliant reverse proxy or API gateway (such as Nginx, Caddy, or HAProxy) to filter and reject malformed Host headers before they reach the ASGI application layer.
Impact:
Potential bypass of path-based authorization or access control checks implemented within custom middleware.
Exposure of restricted endpoints if security decisions rely on reconstructed `request.url.path` rather than the canonical request path.
Low direct system impact unless downstream applications improperly utilize vulnerable URL reconstruction attributes for security gating.
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Sources:
Reported By: github.com
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