What is CVE-2026-40561?

CVE-2026-40561 is a medium-severity vulnerability in Kazuho Starlet, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 5.3/10. Published 2026-05-03.

How severe is CVE-2026-40561?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Vulnerability in Kazuho Starlet

CVE-2026-40561

Starlet versions through 0.31 for Perl allows HTTP Request Smuggling via Improper Header Precedence. Starlet incorrectly prioritizes "Content-Length" over "Transfer-Encoding: chunked" when both headers are present in an HTTP request. Per…

Vulnerability class: HTTP Request Smuggling

EPSS: 0.000 (2.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.

Affected products

Kazuho Starlet — versions 0

Weakness classification (CWE)

CWE-444 — Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling)

References

9b29abf9-4ab0-4765-b253-1875cd9b441e (Third Party Advisory)
9b29abf9-4ab0-4765-b253-1875cd9b441e (Patch, patch)
af854a3a-2127-422b-91ae-364da2661108 (Mailing List, Third Party Advisory)
9b29abf9-4ab0-4765-b253-1875cd9b441e (release-notes)

Frequently asked questions

What is CVE-2026-40561?: CVE-2026-40561 is a medium-severity vulnerability in Kazuho Starlet, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 5.3/10. Published 2026-05-03.
How severe is CVE-2026-40561?: Medium severity. CVSS v3 base score is 5.3 out of 10.