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

Patch nowMedium6.5ExploitedEPSS 70%

CVE-2026-48710 is a HTTP request smuggling in Kludex Starlette, rated medium (6.5 on CVSS 3.1).

Why this priority: Exploited in the wild: listed in CISA's KEV catalog.

Published 26 May 2026 · Updated 1 Oct 2026 · NVD status: Analyzed

What it is

A proxy and the server behind it disagree on where a request ends, so an attacker can slip a second request past the proxy.

How it is reached

An attacker can exploit it over the network, without an account, and nobody has to click anything.

What an attacker gains

The direct impact is limited: partial access to data or a partial outage. In practice, this kind of flaw lets an attacker smuggle requests past the proxy's checks.

Is it being exploited?

CISA added it to the Known Exploited Vulnerabilities catalog on 2026-09-02: it is being exploited in the wild. It can be exploited automatically, at scale. EPSS estimates a 70% chance of exploitation activity in the next 30 days, higher than 99% of scored CVEs.

What to do

Treat it as urgent: it is on CISA's KEV list. CISA's deadline for US federal agencies: 2026-09-16.
Upgrade Kludex Starlette to 1.0.1 or later. The patch notes are linked below.
Until it is patched, keep it off the internet or behind a VPN, allowlist or authenticating proxy.
Check exposed instances for signs of compromise, not only for the version.

Description from 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.

CVSS: Medium6.5v3.1reporterCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Medium6.5v3.1NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Medium6.5v3.1reporterCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Fixed in: starlette: 1.0.1
CISA KEV: Added 2 Sept 2026; federal due date 16 Sept 2026.CISA’s 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.
EPSS: 70% chance of exploitation activity in 30 days; higher than 99% of CVEs (10 Nov 2026).
CISA assessment (SSVC): Exploitation: active · Automatable: yes · Technical impact: partial
Weaknesses: CWE-444 HTTP request smuggling
CWE-1289
Affects: Kludex Starlette
Red Hat Red Hat AI Inference Server 3.3
Red Hat Red Hat Ansible Automation Platform 2.6
Red Hat Red Hat Ansible Automation Platform 2.7
Red Hat Red Hat Migration Toolkit for Applications 8.2
Red Hat Red Hat OpenShift AI 3.3
Red Hat Red Hat OpenShift AI 3.4
Red Hat Red Hat Satellite 6.17
Red Hat Red Hat Satellite 6.18
Red Hat Red Hat Satellite 6.19

What this means for your architecture.

A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.

Components it touches

Operating systems on servers, workstations or devices. Everything on the host inherits the flaw.
Proxies, load balancers and the servers behind them. The flaw sits between a front-end proxy and its back end.

Trust boundaries in play

Internet-facing entry points. No account is needed. Any instance reachable from outside your perimeter, through a load balancer, gateway, VPN or exposed admin port, is in scope.
Between a front-end proxy and its back end. An attacker who crosses it can smuggle requests past the proxy's checks.

Questions to answer about your own systems

Where does Kludex Starlette run in your systems, and at which version?
Which of those instances can be reached from the internet or partner networks?
What can it reach once compromised: which data stores, secrets and services?

See how Veriom maps an architecture Take the interactive tour

Patches and commits

github.com/Kludex/starlette/commit/764dab0dcfb9033d75442d7a359645c9f94648c6

Advisories

Exploits and proofs of concept

Sources

CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.