CVE-2026-48710

Kludex Starlette HTTP Request/Response Smuggling Vulnerability

Actively exploited (CISA KEV) Medium 6.5 CVSS 3.1

Description

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.

Description as published by the source, in English.

Key facts

Published: 2026-05-26
Last modified: 2026-10-01
Assigned by: security-advisories@github.com
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Scored by: nvd@nist.gov (NVD Primary)
Probability of exploitation: 1.8 % higher than 77 % of all known vulnerabilities
EPSS, next 30 days, model v2026.06.15
Fix available: Yes, see references

Actively exploited

CISA added this vulnerability to the Known Exploited Vulnerabilities catalogue on 2026-09-02, with a remediation deadline of 2026-09-16 for US federal agencies.

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.

Affected products

Vendor	Product	Versions	Status
Encode	Starlette	≥ 0.8.3, < 1.0.1	Affected
Redhat	Ai Inference Server	≥ 3.3.0, ≤ 3.3.5	Affected
Redhat	Ansible Automation Platform	2.6	Affected
Redhat	Ansible Automation Platform	2.7	Affected
Redhat	Enterprise Linux Ai	3.0	Affected
Redhat	Migration Toolkit For Applications	< 8.2.0	Affected
Redhat	Openshift Ai	≥ 3.3, < 3.3.5	Affected
Redhat	Openshift Ai	≥ 3.4, < 3.4.2	Affected
Redhat	Openshift Lightspeed	all versions listed	Affected
Redhat	Satellite	6.17	Affected
Redhat	Satellite	6.18	Affected
Redhat	Satellite	6.19	Affected

Weakness type

CWE-1289: Improper Validation of Unsafe Equivalence in Input
The product receives an input value that is used as a resource identifier or other type of reference, but it does not validate or incorrectly validates that the input is equivalent to a potentially-unsafe value.
CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that…

References

https://badhost.org Mitigation, Third Party Advisory
https://github.com/Kludex/starlette/commit/764dab0dcfb9033d75442d7a359645c9f94648c6 Patch
https://github.com/Kludex/starlette/security/advisories/GHSA-86qp-5c8j-p5mr Vendor Advisory
https://github.com/pypa/advisory-database/tree/main/vulns/starlette/PYSEC-2026-161.yaml Third Party Advisory
https://ostif.org/disclosing-the-badhost-vulnerability-in-starlette Mitigation, Third Party Advisory
https://www.secwest.net/starlette Exploit, Mitigation, Third Party Advisory
https://www.x41-dsec.de/lab/advisories/x41-2026-002-starlette Exploit, Mitigation, Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:22992 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:22993 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:23346 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:24866 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:26226 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:30088 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:30089 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:34456 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:34526 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:34532 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:37275 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:43038 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:44696 Third Party Advisory

Related at Berigo

Articles

Seven new KEV entries, three of them in open developer components Mentions this CVE 2026-09-03
CISA added seven new vulnerabilities to its Known Exploited Vulnerabilities catalogue on 2 September 2026. Three of them sit in open components used …

Does this affect you?

A vulnerability matters only if you run the product, in an affected version, somewhere an attacker can reach.

Check your asset list Browse all vulnerabilities

Sources and freshness

CVE

What it is: A reference number naming one specific vulnerability, for example CVE-2024-9474.
What it tells you: Which vulnerability we are talking about, and in which product.
What it does NOT tell you: Nothing about how serious it is, whether anyone is exploiting it, or whether it concerns you.
Why it matters: Without a shared number, vendor, authority and tooling cannot discuss the same flaw.
Used with the others: The number is the key. NVD, KEV and EPSS all describe the same CVE.

NVD CWE CISA KEV EPSS

How to read this together

No single value should be used on its own. A high CVSS score does not mean a vulnerability is being exploited, and a low one does not mean it is harmless. The four sources answer four different questions.

CVE names the specific vulnerability.
NVD adds severity and technical detail about it.
CWE describes the type of mistake behind it.
CISA KEV shows that it is already being exploited.
EPSS estimates how likely exploitation is soon.

The order that decides what is urgent

Do you actually have the product?
Is the version you run affected?
Is it listed in CISA KEV?
Does it have a high EPSS score?
Is the system reachable from the internet or from others?
How important is the system to the business?
Are there compensating controls already in place?

The first two questions are not about the vulnerability at all. They are about you, and they remove most of the list before you start.

A short example

Fix this week

CVSS 6,5 (medium)

In CISA KEV: yes
EPSS: 94 per cent
A firewall facing the internet

Can be scheduled

CVSS 9,8 (critical)

In CISA KEV: no
EPSS: 0,04 per cent
A test server with no internet access

Sorted by CVSS alone, the one on the right comes first. It is the more serious flaw in theory. But the one on the left is being used against real organisations right now, and it sits where an attacker can reach it. That is the one to fix first.

The critical one still has to be fixed. It just does not have to be fixed today.

This product uses the NVD API but is not endorsed or certified by the NVD. CVE and the CVE logo are registered trademarks of The MITRE Corporation; CVE records are used under the CVE Terms of Use. CWE is a trademark of The MITRE Corporation, used per the CWE Terms of Use. KEV data from CISA (CC0). Exploitation probability from EPSS, a FIRST.org project. Open-source package data from OSV and the GitHub Advisory Database (CC-BY 4.0).

Scores and vectors are shown as published by the sources. The ordering of results is Berigo's own editorial assessment, described on the search page, and is not NVD data. An empty result never means a system is safe.