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

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Summary

CVECVE-2026-48710
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-26 22:16:44 UTC
Updated2026-05-26 22:16:44 UTC
DescriptionStarlette 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.

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from [email protected]

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

EPSS: 0.000340000 probability, percentile 0.104460000 (date 2026-05-27)

Problem Types: CWE-444 | CWE-444 CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
3.1CNADECLARED6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Kludex Starlette affected < 1.0.1 Not specified

References

ReferenceSourceLinkTags
ostif.org/disclosing-the-badhost-vulnerability-in-starlette [email protected] ostif.org
github.com/Kludex/starlette/commit/764dab0dcfb9033d75442d7a359645c9f94648c6 [email protected] github.com
github.com/pypa/advisory-database/tree/main/vulns/starlette/PYSEC-2026-1... [email protected] github.com
github.com/Kludex/starlette/security/advisories/GHSA-86qp-5c8j-p5mr [email protected] github.com
badhost.org [email protected] badhost.org
www.secwest.net/starlette [email protected] www.secwest.net
www.x41-dsec.de/lab/advisories/x41-2026-002-starlette [email protected] www.x41-dsec.de
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