CVE-2026-40560Network attack vector

Request smuggling via Content-Length precedence

Published Apr 28, 2026 · Updated Apr 28, 2026

HTTP request smuggling in Tatsuhiko Miyagawa Starman before 0.4018 allows remote attackers to inject requests through a front-end proxy. The Starman::Server::_prepare_env routine reads a supplied Content-Length body before considering Transfer-Encoding: chunked, causing proxy and backend request boundaries to diverge. Exploitation requires a front-end reverse proxy that forwards both conflicting headers; the boundary mismatch permits an extra HTTP request to reach the backend.

CVSS severity7.5
High
EPSS probability0.49%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP request smuggling in Tatsuhiko Miyagawa Starman before 0.4018 allows remote attackers to inject requests through a front-end proxy. The Starman::Server::_prepare_env routine reads a supplied Content-Length body before considering Transfer-Encoding: chunked, causing proxy and backend request boundaries to diverge. Exploitation requires a front-end reverse proxy that forwards both conflicting headers; the boundary mismatch permits an extra HTTP request to reach the backend.

The record

CVE
CVE-2026-40560
Published
Apr 28, 2026
Updated
Apr 28, 2026
Vendor
Tatsuhiko Miyagawa
Product
Starman
Classifications
CWE-444, CAPEC-33, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 28, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 28, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <0.4018

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Tatsuhiko Miyagawa · Starmanversion=0 <0.4018

Published CVSS scores

7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
CAPEC-33HTTP Request Smuggling
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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