---
id: CVE-2026-54282
aliases:
  - GHSA-jp82-jpqv-5vv3
  - PYSEC-2026-248
title: >-
  Starlette: Unvalidated request path concatenated into authority poisons
  request.url.hostname
summary: >-
  Starlette: Unvalidated request path concatenated into authority poisons
  request.url.hostname
severity: low
cvss: 3.7
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N'
vendor: starlette
product: starlette
ecosystem: pip
affected:
  - starlette < 1.3.0
patched:
  - starlette 1.3.0
published: '2026-06-15'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:50:50.050800090Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-jp82-jpqv-5vv3'
references:
  - url: >-
      https://github.com/Kludex/starlette/security/advisories/GHSA-jp82-jpqv-5vv3
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-54282'
  - url: 'https://github.com/Kludex/starlette'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/starlette/PYSEC-2026-248.yaml
  - url: 'https://github.com/advisories/GHSA-jp82-jpqv-5vv3'
tags:
  - osv
  - pip
  - ghsa
epss: 0.00273
epssPercentile: 0.17583
cwe:
  - CWE-20
  - CWE-706
ingestedAt: '2026-07-07T15:41:58.627Z'
---

## Overview

### Summary

In affected versions, the HTTP request path is not validated before being used to reconstruct `request.url`. Because `request.url` is rebuilt by concatenating `{scheme}://{host}{path}` and re-parsing the result, a path that does not begin with `/` (for example `@google.com`) moves the authority boundary during re-parsing, so `request.url.hostname` and `request.url.netloc` become attacker-controlled. Code that reads `request.url.hostname` (rather than the `Host` header or `scope`) can therefore be misled into trusting an attacker-supplied host.

### Details

When a client requests a path that does not start with `/`:

```http
GET @google.com HTTP/1.1
Host: localhost
```

affected versions reconstruct the URL as `http://localhost@google.com`. Per [RFC 3986 §3.2.1](https://www.rfc-editor.org/rfc/rfc3986.html#section-3.2.1), the substring before `@` in the authority is `userinfo`, so re-parsing yields `username = "localhost"` and `hostname = "google.com"`, with an empty path:

```text
request.url          == "http://localhost@google.com"
request.url.hostname == "google.com"
request.url.path     == ""
```

The root cause is that the path is concatenated directly after the host without a separating `/`, and without validating that it begins with one. Only the `Host` header was validated when constructing `request.url`; the path was not.

This requires an ASGI server that forwards a request-target lacking a leading `/` into `scope["path"]`.

### Impact

Any application running an affected version that uses `request.url`, `request.url.netloc`, or `request.url.hostname` for a security-sensitive decision (host-based authorization, redirect/callback base, SSRF target, cache key, audit log) may be affected, when no fronting proxy or load balancer rejects the malformed request-target first.

Note that this is less exploitable than [GHSA-86qp-5c8j-p5mr](https://github.com/Kludex/starlette/security/advisories/GHSA-86qp-5c8j-p5mr): there, the poison is carried in the `Host` header, so the real path still routes to a valid endpoint while `request.url.path` lies. Here, the poison must be carried in the path itself, and that path (`@google.com`) does not match any registered route, so routing returns `404` and no endpoint handler runs. The exposure is limited to code that reads `request.url` before routing - notably middleware - or in 404/exception handlers.

### Mitigation

Upgrade to a patched version, which prevents the request path from crossing into the URL authority. The request above instead yields `http://localhost/@google.com` with `request.url.hostname == "localhost"`.

## Affected packages

- `starlette < 1.3.0`

## Remediation

Upgrade to a patched release:

- `starlette 1.3.0`