CVE-2026-40561

Summary

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 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.

Affected Software

Weaknesses

• CWE-444: CWE-444 Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

Workarounds

Migrate to Starman 0.4018 or later which has fixed this issue or apply the patch.

ADP Enrichment

CVE Program Container

Additional References

• http://www.openwall.com/lists/oss-security/2026/05/03/1

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: yes
  • Technical Impact: partial

References

• https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.3
• https://github.com/kazuho/Starlet/commit/a7d5dfd1862aafa43e5eaca0fdb6acf4cc15b2d0.patch
• https://metacpan.org/release/KAZUHO/Starlet-0.32/changes

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