CVE-2026-48710

Summary

Starlette is a lightweight ASGI framework/toolkit. Prior to version 1.0.1, 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. Users should upgrade to a version greater than or equal to version 1.0.1, which validates the `Host` header against the grammar of RFC 9112 §3.2 / RFC 3986 §3.2.2 when constructing `request.url` and falls back to `scope["server"]` for malformed values.

Impact & exploitability

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

Affected products we track (1)

Recommendation

This vulnerability is being actively exploited in the wild — patch affected products urgently. Open any affected product above for its exact safe version.

Official patch: https://github.com/Kludex/starlette/commit/764dab0dcfb9033d75442d7a359645c9f94648c6 ↗

Additional information

• NVD record
• https://github.com/Kludex/starlette/commit/764dab0dcfb9033d75442d7a359645c9f94648c6Patch
• https://github.com/Kludex/starlette/security/advisories/GHSA-86qp-5c8j-p5mrAdvisory
• https://badhost.orgAdvisory
• https://ostif.org/disclosing-the-badhost-vulnerability-in-starletteAdvisory
• https://www.secwest.net/starletteAdvisory
• https://www.x41-dsec.de/lab/advisories/x41-2026-002-starletteAdvisory
• https://github.com/pypa/advisory-database/tree/main/vulns/starlette/PYSEC-2026-161.yamlAdvisory
• https://access.redhat.com/errata/RHSA-2026:22992Advisory