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GHSA-86qp-5c8j-p5mr

Dashboard / Vulnerabilities / GHSA-86qp-5c8j-p5mr

GHSA-86qp-5c8j-p5mr

Published: 4 Jun 2026Last Modified: 28 Aug 2026

Aliases:

Summary: Starlette has missing Host header validation that poisons request.url.path, bypassing path-based security checks

Details: ### Summary In affected versions, 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. ### Details When a client requests `http://example.com/foo`, it sends: ```http GET /foo HTTP/1.1 Host: example.com ``` Affected versions reconstructed the URL by concatenating `http://{host}{path}` and re-parsing the result. The `Host` value is only valid as a `uri-host [ ":" port ]` per [RFC 9112 §3.2](https://www.rfc-editor.org/rfc/rfc9112.html#section-3.2-6), where `uri-host` follows the restricted `host` grammar of [RFC 3986 §3.2.2](https://www.rfc-editor.org/rfc/rfc3986.html#section-3.2.2). When it contains characters outside that grammar - notably `/`, `?`, or `#` - those characters move the path/query/fragment boundaries during re-parsing, so the parsed `request.url.path` no longer matches the path the server actually received. For example: ```http GET /foo HTTP/1.1 Host: example.com/abc?bar= ``` reconstructs to `http://example.com/abc?bar=/foo`, whose parsed `path` is `/abc` - even though routing used the real path `/foo`. The router still dispatches to `/foo` and the endpoint executes, but any middleware or code that reads `request.url.path` sees `/abc`, so path-based authorization checks can be bypassed. ### Impact Any application running an affected version that relies on `request.url` (or `request.url.path`) for security-sensitive decisions is affected. The most common case is middleware that gates access to certain path prefixes based on `request.url.path`. Deployments fronted by a proxy or load balancer are mitigated only if that proxy rejects or normalizes the malformed `Host` header before forwarding and the application does not trust attacker-controlled host headers (e.g. `X-Forwarded-Host`) elsewhere. ### Mitigation Upgrade to a patched version, which validates the `Host` header against the grammar of [RFC 9112 §3.2](https://www.rfc-editor.org/rfc/rfc9112.html#section-3.2-6) / [RFC 3986 §3.2.2](https://www.rfc-editor.org/rfc/rfc3986.html#section-3.2.2) when constructing `request.url` and falls back to `scope["server"]` for malformed values.

Affected packages

Package

Name: starlette

Purl: pkg:pypi/starlette

Affected ranges

Type: ECOSYSTEM

Events:

Introduced- 0

Fixed -1.0.1

Affected versions

0.1.0

0.1.1

0.1.10

0.1.11

0.1.12

0.1.13

0.1.14

0.1.15

0.1.16

0.1.17

0.1.2

0.1.3

0.1.4

0.1.5

0.1.6

0.1.7

0.1.8

0.1.9

Common Vulnerability Scoring System

Attack Vector

Network

Adjacent

Local

Physical

Privileges Required

None

Low

High

User Interaction

None

Required

Scope

Unchanged

Changed

Confidentiality

None

Low

High

Integrity

None

Low

High

Availability

None

Low

High