PT-2026-49596 · Pypi · Starlette

Published

2026-06-15

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Updated

2026-06-15

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CVE-2026-54282

CVSS v3.1

3.7

Low

VectorAV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

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 /:
GET @google.com HTTP/1.1
Host: localhost
affected versions reconstruct the URL as http://localhost@google.com. Per RFC 3986 §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:
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: 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".

Fix

RCE

Weakness Enumeration

CWE-706CWE-20

Related Identifiers

CVE-2026-54282
GHSA-JP82-JPQV-5VV3

Affected Products

Starlette