---
title: "CVE-2026-48710: Kludex Starlette HTTP Request/Response Smuggling Vulnerability"
url: https://erroneo.us/security/cve/CVE-2026-48710/
description: "CVE-2026-48710 (Kludex Starlette): Exploited in the wild (CISA KEV). Starlette is a lightweight ASGI framework/toolkit. Prior to version 1.0.1, the HTTP…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-05-26
date_modified: 2026-10-01
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-48710"
kev: true
cvss: 6.5
epss: 0.07056
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-48710: Kludex Starlette HTTP Request/Response Smuggling Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run Kludex Starlette. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-09-02, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-09-16 ; treat that as the outer limit, not the target.
- EPSS 7.1% , percentile 94: FIRST’s model estimates a 7.1% chance of exploitation activity in the next 30 days, higher than 94% of all scored CVEs (elevated). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Editorial verdict: Patch this week. Starlette BadHost: Host Header Auth Bypass in CISA KEV — Bump starlette to 1.0.1 or later in every Python service this week; it is urgent where an ASGI server faces untrusted clients directly and middleware makes security decisions from request.url.

## What it is

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.

## Affected products (CVE record)

- Kludex starlette: < 1.0.1

## Severity

- GitHub_M CVSS 3.1: 6.5 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N`
- redhat-SADP CVSS 3.1: 6.5 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N`

## Exploitation

- CISA KEV: added 2026-09-02; federal due date 2026-09-16. Known ransomware use: Unknown.
- 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.
- CISA SSVC assessment: exploitation active , automatable yes , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 7.06% probability of exploitation activity in the next 30 days; percentile 94.

## Sources

- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:30089)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:30088)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:24866)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:23346)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:43038)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:37275)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:60520)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:34456)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:44696)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:22993)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:26226)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:51357)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:22992)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:34532)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:34526)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:63337)
- [Listed in CISA KEV notes (github.com)](https://github.com/Kludex/starlette/security/advisories/GHSA-86qp-5c8j-p5mr)
- [CVE.org record CVE-2026-48710](https://www.cve.org/CVERecord?id=CVE-2026-48710)
- [NVD entry CVE-2026-48710](https://nvd.nist.gov/vuln/detail/CVE-2026-48710)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-48710)
- [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk)
- [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk)
- [github.com](https://github.com/Kludex/starlette/commit/764dab0dcfb9033d75442d7a359645c9f94648c6)
- [badhost.org](https://badhost.org)
- [github.com](https://github.com/pypa/advisory-database/tree/main/vulns/starlette/PYSEC-2026-161.yaml)
- [ostif.org](https://ostif.org/disclosing-the-badhost-vulnerability-in-starlette)
- [secwest.net](https://www.secwest.net/starlette)
- [x41-dsec.de](https://www.x41-dsec.de/lab/advisories/x41-2026-002-starlette)
- [wiz.io](https://www.wiz.io/blog/ai-infrastructure-honeypot)
- [access.redhat.com](https://access.redhat.com/security/cve/CVE-2026-48710)
- [RHBZ#2481742](https://bugzilla.redhat.com/show_bug.cgi?id=2481742)
- [security.access.redhat.com](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-48710.json)

---
Source page: https://erroneo.us/security/cve/CVE-2026-48710/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt