CVE-2026-40560
Miyagawa Starman ≤ 0.4018
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:NSummary
CVE-2026-40560 is a high-severity HTTP Request/Response Smuggling (CWE-444) vulnerability in Miyagawa Starman. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 40th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SC-7 (Boundary Protection) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-40560 is an HTTP request smuggling vulnerability affecting Starman, a Perl PSGI server, in versions prior to 0.4018. The flaw stems from Starman's incorrect prioritization of the "Content-Length" header over "Transfer-Encoding: chunked" when both are present in an HTTP request, violating RFC 7230 Section 3.3.3, which mandates that Transfer-Encoding takes precedence. This misinterpretation enables request smuggling attacks and is classified under CWE-444 with a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N).
Remote attackers can exploit this vulnerability by sending crafted HTTP requests through a front-end reverse proxy to the vulnerable Starman instance. No privileges or user interaction are required, allowing unauthenticated network adversaries to smuggle malicious requests that the proxy interprets differently from the backend server, potentially leading to high confidentiality impacts such as unauthorized data disclosure.
Mitigation involves upgrading to Starman version 0.4018 or later, where the issue is addressed via a specific commit that corrects header precedence handling. Relevant advisories, including the OSS-security mailing list announcement from April 29, 2026, and the project's changelog on MetaCPAN, confirm the patch details and release notes.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-26189
Vulnerability Data
Starman versions before 0.4018 for Perl allows HTTP Request Smuggling via Improper Header Precedence. Starman incorrectly prioritizes "Content-Length" over "Transfer-Encoding: chunked" when both headers are present in an HTTP request. Per RFC 7230 3.3.3, Transfer-Encoding must take precedence. An attacker…
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could exploit this to smuggle malicious HTTP requests via a front-end reverse proxy.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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Mitigating Controls (NIST 800-53 r5) AI
Boundary protection at external interfaces can enforce consistent HTTP request/response parsing rules between intermediaries and endpoints.
Validating HTTP inputs at the intermediary prevents malformed messages from being interpreted inconsistently downstream.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Configuration management can enforce uniform HTTP parsing rules across intermediaries, directly mitigating inconsistent interpretation.
Network monitoring can detect smuggling attempts via anomalous HTTP traffic or logs, while eliminating the inconsistency directly aids detection of such events.
Network protections can enforce consistent HTTP proxy/firewall behavior to block smuggling, and removing the weakness helps prevent unauthorized access via request smuggling.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing can detect HTTP request smuggling vulnerabilities in intermediary components.
Network security controls can enforce consistent HTTP parsing and proxy behavior that mitigates request smuggling.
Secure network services include hardening proxies and gateways against inconsistent HTTP interpretation.
Secure SDLC practices require threat modeling and testing for HTTP parsing inconsistencies in intermediaries.
Application security requirements can mandate strict HTTP message validation and canonicalization.
Secure architecture principles include consistent protocol handling and defense-in-depth for proxies.