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

Exploitation

Confirmed: listed in the CISA Known Exploited Vulnerabilities catalog.

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS

• CVE-2026-48710: 70.29% estimated exploitation activity in the next 30 days; percentile 99.39 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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: 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, where uri-host follows the restricted host grammar of RFC 3986 §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…

Published by the source

4 Jun 2026, 13:15 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 13:50 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-86qp-5c8j-p5mr

2. Revision 2 · evidence added · 24 Oct 2026

   CISA KEV confirmed exploitation for CVE-2026-48710 (date added 2026-09-02). Customer workflow unchanged.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-86qp-5c8j-p5mr

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# Patch Next advisory brief: CVE-2026-48710

Advisory: Starlette has missing Host header validation that poisons request.url.path, bypassing path-based security checks
IDs: CVE-2026-48710, GHSA-86qp-5c8j-p5mr
Record: https://patchnext.com/advisories/cve-2026-48710 (revision 3, source checked 26 Oct 2026, 13:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: confirmed: listed in the CISA Known Exploited Vulnerabilities catalog.
Vendor response: Vendor fix available; fixed versions by package: starlette 1.0.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI starlette: affected <= 1.0.0; fixed in 1.0.1

## Suggested inspection (read-only)
- `python -m pip show starlette`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on starlette.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-86qp-5c8j-p5mr (OSV record GHSA-86qp-5c8j-p5mr lists affected ranges: PyPI starlette >=0 <1.0.1 (fixed))
- Verified: https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json (CISA added CVE-2026-48710 to the Known Exploited Vulnerabilities catalog on 2026-09-02.)
- Verified: https://github.com/advisories/GHSA-86qp-5c8j-p5mr (GitHub-reviewed advisory GHSA-86qp-5c8j-p5mr lists affected ranges: PyPI starlette >=0 <=1.0.0)
- Verified: https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CISA added CVE-2026-48710 to the Known Exploited Vulnerabilities catalog on 2026-09-02.)

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