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KEV catalog · CISA Known Exploited Vulnerabilities

CVE-2026-48710 6.5
Kludex · Starlette · Added 2026-09-02 · Published 2026-05-26
3-Day Required PoC Available KEV Automatable Active Exploitation

Details

VulnerabilityKludex Starlette HTTP Request/Response Smuggling Vulnerability
VendorKludex
ProductStarlette
Date added2026-09-02
Due date2026-09-16
CISA catalogView on CISA KEV catalog
Required actionApply 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.
CWECWE-1289 CWE-444
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Descriptions

KEV: Kludex Starlette contains a HTTP request/response smuggling vulnerability that could allow attackers to inject paths into the host part, prepending the actual path leading to issues such as authentication bypass when the authentication depends on the reconstructed URL’s path. This vulnerability could be chaned with CVE-2026-42271.

NVD: 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.

Compliance SSVC + BOD 26-04

Automatableyes
Technical impactpartial
Exploitation statusactive
3-day qualifyingYes
Public timeline3 days
Non-public timeline14 days
Forensic (public)Not required
Forensic (non-public)Not required

Research metadata

Last researched2026-09-02 18:39 UTC
Component defaultyes
Sources https://github.com/Kludex/starlette/security/advisories/GHSA-86qp-5c8j-p5mr
https://github.com/Bhanunamikaze/BadHost-CVE-2026-48710-Exploit
https://www.sentinelone.com/vulnerability-database/cve-2026-48710/
https://www.csoonline.com/article/4177711/fastapi-based-ai-tools-exposed-to-authentication-bypass-by-flaw-in-starlette-framework.html
https://ccb.belgium.be/advisories/warning-vulnerability-starlette-framework-and-related-frameworks-fastapi-exposes

Hunting hypothesis agent

Hunt access logs for requests with malformed Host headers containing path characters (e.g. Host: target.com/health?x=). Monitor WAF for Host header injection — stock access logs may not capture full header values.

Research details

Componentrequest.url Host header reconstruction (URL path parsing from Host header)
PreconditionsNetwork reachability to a Starlette/FastAPI application running Starlette <= 1.0.0; no authentication required; the application must use request.url.path for security decisions (e.g. path-based authorization middleware) rather than scope['path']; versions prior to 1.0.1 affected, fixed in 1.0.1 agent
Public PoCyes
PoC URLs https://github.com/Bhanunamikaze/BadHost-CVE-2026-48710-Exploit
https://github.com/SecureWithUmer/CVE-2026-PoCs Third-party repos; verify before use.
Advisoryhttps://github.com/Kludex/starlette/security/advisories/GHSA-86qp-5c8j-p5mr
Exploit notesDetection-only scanner available (Bhanunamikaze). The scanner tests Host header injection using two strategies (Host and X-Forwarded-Host carriers) with OpenAPI spec discovery. The vulnerability itself requires crafting a Host header containing path characters (e.g. Host: example.com/health?x=) to poison request.url.path. Public PoC confirms exploitation path. CVSS attack complexity: LOW
SummaryCVE-2026-48710 (BadHost) is a Host header validation bypass in Starlette ASGI framework versions before 1.0.1. A malformed Host header containing path characters (e.g. /, ?, #) poisons request.url.path during URL reconstruction, causing it to differ from the actual routed path. Middleware using request.url.path for authorization can be bypassed. A detection-only scanner exists; active exploitation has been observed when chained with CVE-2026-42271 (LiteLLM RCE).

Tia coverage

First reported2026-05-28
First exploit report2026-06-09
Exploit report → KEV85 days before the listing

When Tia's reporting first covered this CVE and whether a report claimed exploitation before the KEV listing. Lead-time deltas are measured from the exploitation report only — plain coverage is not exploitation intel. See the story links under Mentioned in for coverage detail.

Mentioned in

active-exploitation-of-cisco-secure-firewall-management-center-vbadhost-cve-2026-48710-starlette-host-header-injection-bypasseshackers-target-litellm-ragflow-and-kestra-ai-infrastructure-to-s

Record schema v1.0. Enrichment is research-grade, not a substitute for analyst review.

Source on GitHub