Kludex Starlette HTTP Request/Response Smuggling Vulnerability
Kludex — starlette
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.
6.5
2.1%
Vector 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
- Published
- May 26, 2026
- Modified
- Oct 1, 2026
- Added to KEV
- Sep 2, 2026
- Federal patch due
- Sep 16, 2026
CISA required action
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
Weakness classification
Affected packages
Proof-of-concept & exploitation references
5 foundWeaponization
Public repositories whose name or description references CVE-2026-48710, found via a live GitHub search at request time. These are community-sourced signals, not a verified working exploit — cross-check each one before relying on it, and treat higher star counts and recent activity as (weak) corroboration, not proof.
- eris-ths/supply-chain-guard★ 3
Detect, assess, and respond to supply chain attacks across npm/yarn and Python (pip/poetry/uv). Claude Code skill + standalone scripts. Built during axios RAT (2026-03-31) and Starlette BadHost CVE-2026-48710 (2026-05-22).
updated Jul 2, 2026
- Bhanunamikaze/BadHost-CVE-2026-48710-Exploit★ 1
Detection scanner for CVE-2026-48710 - Host-header auth bypass in Starlette/FastAPI
updated Jul 9, 2026
- xtremebeing/starlette-host-header-lab★ 1
Starlette Host-Header URL Confusion Lab (X41-2026-002) - CVE-2026-48710
updated May 27, 2026
- CuteeCat/CVE-2026-48710★ 0
CVE-2026-48710漏洞验证代码
updated Aug 11, 2026
- sb-ox/repro-OXDEV-77637-uv-workspace★ 0
OXDEV-77637 repro fixture: uv workspace whose transitive CVE (starlette 0.25.0 / CVE-2026-48710) is dropped when the lean clone omits workspace-member pyproject.toml. Tag: repro-OXDEV-77637
updated Aug 3, 2026
References
Frequently asked questions
What is 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.
How severe is CVE-2026-48710?
CVE-2026-48710 has a CVSS base score of 6.5 out of 10 (CVSS 3.1).
Is CVE-2026-48710 actively exploited in the wild?
Yes. CVE-2026-48710 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added Sep 2, 2026, meaning CISA has confirmed evidence of active exploitation.
What is the EPSS score for CVE-2026-48710?
2.1% - meaning FIRST.org's EPSS model estimates a 2.1% probability this vulnerability will be exploited in the wild within 30 days (80% percentile among all scored CVEs).
Is there exploit tooling available for CVE-2026-48710?
Yes - a public Nuclei template referencing CVE-2026-48710 exist in public repositories we checked. We also found 5 public GitHub repositories referencing this CVE.
What type of vulnerability is CVE-2026-48710?
CVE-2026-48710 is classified under CWE-444, CWE-1289 (CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')).
Cross-checked against
Impactr finds and proves whether CVE-2026-48710 — or flaws like it — are actually reachable in your own web apps and APIs, with a reproducible exploit as evidence.