Vulnerability Report

CVE-2026-48710

Title: Host Header Validation Bypass in Starlette

Other

Proof Of Concept

PoC Available for CVE-2026-48710

CWE Category CWE-444
Published Date May 26, 2026
Modified Date Jun 16, 2026
Exploit Status Available
Score 6.5 CVSS v3.1
Exploit Probability (EPSS)
1.00%

Vulnerability Summary

CVE-2026-48710: 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.

Impacted Vendors

E
encode 1

Reference Links

https://badhost.org https://github.com/Kludex/starlette/commit/764dab0dcfb9033d75442d7a359645c9f94648c6 https://github.com/Kludex/starlette/security/advisories/GHSA-86qp-5c8j-p5mr https://github.com/pypa/advisory-database/tree/main/vulns/starlette/PYSEC-2026-161.yaml https://ostif.org/disclosing-the-badhost-vulnerability-in-starlette https://www.secwest.net/starlette https://www.x41-dsec.de/lab/advisories/x41-2026-002-starlette
CVSS v3.1
Source Entity [email protected]
Severity MEDIUM
6.5
Attack Vector
NETWORK
Complexity
LOW
Privileges
N/A
Interaction
NONE
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
UNCHANGED
RAW VECTOR CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
CVSS v3.1
Source Entity [email protected]
Severity MEDIUM
6.5
Attack Vector
NETWORK
Complexity
LOW
Privileges
N/A
Interaction
NONE
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
UNCHANGED
RAW VECTOR CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
CVSS v3.1
Source Entity 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Severity MEDIUM
6.5
Attack Vector
NETWORK
Complexity
LOW
Privileges
N/A
Interaction
NONE
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
UNCHANGED
RAW VECTOR CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Associated Attack Patterns (CAPEC)

Total: Patterns

CVE-2026-48710 Exploits & PoCs (Proof Of Concept)

GitHub https://github.com/xtremebeing/starlette-host-header-lab
View Code
GitHub https://github.com/eris-ths/supply-chain-guard
View Code
MODIFIED

Vulnerability data updated via NVD.

MODIFIED

Vulnerability data updated via NVD.

MODIFIED

Vulnerability data updated via NVD.

MODIFIED

Vulnerability data updated via NVD.

Attack Vector Matrix

Access Vector NETWORK
Complexity LOW
Privileges N/A
Interaction NONE
CVSS Vector String CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Affected Stack

No specific products linked.