CVE-2026-54282

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://[email protected]. 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://[email protected]"
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"].

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".

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.

The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.

CVE-2026-54282 has a CVSS score of 3.7 (Low). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.3.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-54282? CVE-2026-54282 is a low-severity improper input validation vulnerability in Starlette (pip), affecting versions < 1.3.0. It is fixed in 1.3.0. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
2. How severe is CVE-2026-54282? CVE-2026-54282 has a CVSS score of 3.7 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of Starlette are affected by CVE-2026-54282? Starlette (pip) versions < 1.3.0 is affected.
4. Is there a fix for CVE-2026-54282? Yes. CVE-2026-54282 is fixed in 1.3.0. Upgrade to this version or later.
5. Is CVE-2026-54282 exploitable, and should I be worried? Whether CVE-2026-54282 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-54282 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-54282? Upgrade Starlette to 1.3.0 or later.